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From the Mahans Thermal Products team.

Is a Custom Heat Exchanger the Right Fit for Your Facility?

If you’re in the market for a new heat exchanger, it’s understandable if you aren’t quite sure where to begin when it comes to making a decision. You need a heat transfer system that’s as energy efficient as possible. It needs to be capable of functioning efficiently using your facility’s available utilities. It needs to be right for your space when it comes to size, dimensions, and construction material as well.

Every detail needs to be just so. Anything less than exactly the right fit, and your facility could be losing a small fortune in lost productivity and wasted energy. That’s exactly why it’s so important to understand that your options aren’t limited to only the existing heat exchangers out there on the market. Do you have special production needs or a unique space layout that can’t accommodate just any heat transfer system? A custom-built heat exchanger might be the solution you’ve been looking for. The following are just a few of the potential benefits.

Guaranteed Optimal Performance

Each industrial process is unique and complex. No two are exactly alike. That said, choosing the right heat exchanger means having a thorough understanding of all the specifications, requirements, and challenges involved. Sometimes a standard shell and tube or plate style heat exchanger just isn’t capable of covering all the bases. Settling for one anyway can mean that you’re not getting everything you could be out of your investment.

Letting a top notch thermal expert like Mahan’s Thermal thoroughly evaluate your needs and build you a system with your unique application in mind guarantees you the most efficient possible solution for you. Any temperature fluctuations or flow patterns unique to your process will be fully accommodated. You’ll enjoy the absolute peace of mind that comes with knowing your system is functioning as efficiently as is humanly possible.

More Options for Tough-to-Fit Spaces

Not every facility has an unlimited amount of space to work with when it comes to installing something like a heat exchanger. Sometimes limitations can be accommodated by an existing model or a compromise can safely be made. However, a custom built heat exchanger opens your range of options up in completely new ways you may not have considered before.

Is there a particular brand, model, or type of heat exchanger that would work particularly well for your purposes, but which may not be compatible with your current space limitations as is? Speak to a heat transfer expert about having a system designed around the space you’re working with. The chances are excellent that something specific you thought wasn’t an option could be perfectly feasible with a couple of alterations.

Increase Energy Efficiency with Cost-Effective Solutions

The better the fit a given heat exchanger is for a particular process or facility, the more energy-efficient it’s ultimately going to be. When it comes to a big industrial facility, every connection and detail can make a significant difference. A custom-designed heat exchanger can guarantee that every requirement is met to perfection.

Not only does attention to energy efficiency help improve your business’s bottom line and safeguard your budget, but it helps you make sure your carbon footprint is as reasonable as possible. You’ll be doing your part to help preserve the environment, as well as giving your customers an excellent reason to choose your business over the competition. Here in the 21st century, everyone wants to feel good about the choices they make from an eco-friendly standpoint, and your clients are no exception.

Getting a System Custom Designed Is Easier Than You Think

The heat transfer experts at Mahan’s Thermal Products specialize in designing a wide range of different heat exchangers for a multitude of different applications. These include, but are not limited to, district heating, heat pumps, condensers, oil coolers, evaporators, and process heating.

Your Mahan’s heat exchanger will be meticulously designed using high performance parts from only the very best, most widely trusted brand names in the industry. Every measurement, specification, and detail will be taken into consideration at every stage of the process. The result will be a cost-effective heat transfer solution that is guaranteed to be the perfect fit for your space and unique application.

When you choose Mahan’s, you’re getting more than just the very best heat exchangers money can buy. You’re gaining a valuable business partner that can help you make sure your system stays efficient and economical into the future. Let’s get started today!

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Shell and Tube Heat Exchangers

Shell and Tube Heat Exchangers

Choosing the Right Side for Your Liquids

one of the most important design considerations one must make when designing a shell and tube heat exchanger is fluid selection. choosing the right fluids and selecting which fluid will be used in the shell side and which will be used on the tube side, often affects other design considerations like zone definition, area of the exchanger, flow- rates, and the materials that may be best suited to the purpose for which the exchanger is being designed.

Although fluid selection often includes intricate decisions based on factors like ther- mal stability, pressure considerations, economy, and pump-ability, there are some basic categories of fluids that can help to narrow down your selection based on the general properties of the fluids.

Basic fluid categories include:

  • Synthetic organic or silicone fluid; or
  • Inhibited glycol-based fluid.

Based on your temperature requirements for your heat exchanger, make a selection between the above categories of fluid. If your temperature requirements exceed 175 ̊C or 350 ̊F, then you should probably consider the synthetic organic or the silicone based fluids. If your requirements are for temperatures that are lower than 350 ̊F, then inhibited glycol-based fluids are most likely best suited for the heat exchanger.

Once you have chosen your fluids, it is time to decide which fluid is best for the shell side and which is best for use on the tube side. Although there are numerous factors to consider, there are some basic rules that can help you to determine which fluid is best suited to the tube and which is best for the shell

Factors that can be used to determine the
best fluids for each application include:

  • Pressure
  • Fouling
  • Material involved
  • Potential pressure drops
  • Vapor
  • Viscous services
  • Solidifying services


If you are designing a heat exchanger for high pressure applications, then you need to make a decision about where to place the high-pressure fluids.Choosing to place the high pressure fluid on the tube side allows you to reduce or minimize the exchanger manufacture cost.

Since the diameter of the tubing is smaller on the tube side, you will most likely require less material with high-pressure ratings on the tube side than on the larger shell side. Metal thickness on the tube side will carry a higher pressure rating than the same metal thickness on the larger shell side that may have cost implications for your design.


Another consideration to take into account when selecting the fluids for the shell and tube sides is the potential of the liquids you have chosen to foul. Essentially, this consideration is based on how easy it will be to clean the heat exchanger and the implications of fouling for the overall function of the heat exchanger.

To make the right choice, you need to consider the heat exchanger configuration you have chosen to work with. Straight tubes, for example, are far easier to clean than U-tubes. A fixed tubesheet may make the shell side of your heat exchanger impossible to clean, in which case a fouling liquid would be an extremely bad idea. A square tube pattern can make the shell side of your shell and tube heat exchanger easier to clean, allowing you to place your fouling liquid in this area.

Essentially, the prime considerations, in terms of fouling, are how easy it will to clean the exchanger and the potential of fouling to ruin the system. If the liquid is prone to fouling and the shell side is going to be almost impossible to clean, you should rather place the liquid on the tube side.

If the shell side is the better option for the fouling liquid, then fouling reduction steps like the addition of helical baffles may be the best solution, assuming that your fouling liquid has to be placed on the shell side.

The type of fouling involved may also help you to make the best decision about liquid and materials, and on which side to place the fouling liquid.

There are various different types of fouling, depending on the conditions of the heat exchanger and the fluid selection. Common types of fouling include crystallization, organic growth, sedimentation, fouling due to chemical reaction coking, and fouling due to chemical corrosion.


Fouling due to crystallization occurs when the solubility of salts naturally present in certain types of fluids are sensitive to temperature. If the fluid is heated during the cooling process, salts may dissolve and then crystalize when the liquid cools. This heating, then cooling often results in the crystals forming as scale on the surface. Selecting another liquid or adjusting the temperatures of the heat transfer may offer solutions in this type of case.


Fresh water as a fluid choice can result in the deposition of sand, rust, or other compounds, and this must be taken into account when choosing the right side for these types of liquids. Adjusting the velocity of the heat exchanger may also offer a solution where these types of liquids are chosen.

Biological Organic Growth

The exchanger materials and fluids must be carefully considered in terms of their chemical composition. Where the materials used and the fluids chosen can react with one another, these chemical reactions must be taken into account, and potential resultant fouling must be considered. Where there is a high chance of this type of fouling, changes in either material or liquid should be seriously considered.

Fouling Due to Corrosion

Biological growth is not the only reaction that can occur where materials chosen are less than ideal. Where fluids and materials react in the form of corrosion, the fluid can destroy the surfaces of the heat exchanger, and this can result in expensive repairs. Corrosion can affect the heat transfer capabilities of the equipment, and it is therefore vital to consider the properties of both the materials and fluids to avoid corrosion where possible.

Fouling Due to Chemical Reaction Coking

Chemical reaction coking occurs where the liquid chosen deposits hydrocarbons in high temperature applications. In this case, adjusting the temperature between the heat transfer surface and the fluid may offer a solution.

Material Involved

Another consideration, when choosing your liquids and deciding which is the right side to place them, is about the materials used to construct the heat exchanger itself and the nature of the fluids you have chosen to include in your design.

Corrosive fluids will cause a certain amount of damage to the system. To offset the potential corrosive damage, you will need to select corrosion resistant alloys and materials, and these will drive up the costs of your heat exchanger design.

Choosing to place the corrosive liquid on the tube side rather than the shell side can help to limit the damage caused and the costs involved in replacing these components. Since only the tube side will require the more expensive materials rather than the entire exchanger, choosing the tube side may make more sense financially and in terms of replacement costs.

Potential Pressure Drops

Where the fluid chosen has the potential for pressure drops or a low pressuredrop, you should place this fluid on the shell side of the exchanger. If the shell side pressure drops need to be reduced further, then the following strategies can be considered:

  • You could change the baffle type you have chosen from segmental to double segmental, and this may help to decrease the flow velocity in the shell side. This could result in a lower pressure drop.
  • You could increase the baffle spacing to increase the cross flow area.The increase in baffle spacing can help to reduce the pressure drop, since it reduces cross flow velocity.
  • You could increase the baffle cut to help reduce window velocity and increase window flow area. Increasing the baffle cut could result in a decreased pressure drop, although this approach has a limited impact, since it will only affect window pressure drop, as opposed to total pressure drop.
  • You could choose to use no-tubes-in-window type baffles, and you can increase the spacing as necessary. No-tubes-in-window type baffles may, however, result in lower heat transfer volume to area ratios, and this could in turn result in higher costs that must also be taken into account.
  • You could investigate other types of shell design, since some shell types offer fewer pressure drops.


If you are working with vapors, or require vapor in the heat exchanger, then it is best to use the vapor on the shell side rather than on the tube. Vapors normally require higher volumes, and they offer a lower heat-transfer coefficient. Placing vapors on the shell side can help to reduce pressure drops for a particular volume. It will also generally offer higher heat transfer coefficients.

Condensing Services

If condensing services are required, you should try to place the condensing fluid on the shell side, rather than the tube side, although there are also other considerations that need to be taken into account for condensing services.

Where the condensing liquids are relatively pure, and where the condensing range between the liquids is relatively narrow, the configuration of the exchanger may not be that important, but where mixtures have a wide condensing range configuration, the exchanger may require more consideration. With wide condensing range mixtures, flow patterns inside the exchanger should be carefully chosen to ensure that the liquids and vapors inside the exchanger remain mixed.

Shell-side velocity must be high enough to reduce the vapor and liquids separating inside the exchanger. Liquid that drops out can make the vapor leaner, and this can affect the temperature that is required to condense from the vapor.

Wide condensing range mixtures may also require that you design an exchanger where the fluid leaves from the bottom to help force liquid into the vapor mix. You may also need to consider your choice of baffling, selecting a horizontal, rather than a vertical baffle cut.

Viscous Services

Viscous services can require complex decision making, and you need to consider various factors and be ready to make a variety of compromises in terms of your heat exchanger design.

If you have a viscous fluid on the tube side, it may result in low heat transfer and a high pressure drop, which may mean that a shell-side application in this case may be preferable. Choosing the shell-side, however, may not be without disadvantages. A high pressure drop on the shell side may result in vibration damage and may also require flow bypassing around the baffles. If, however, a shell-side
application is necessary, then there are shell-side modifications that may be made to limit the damage and other disadvantages.

Solidifying Services

Although shell and tube exchangers can be designed for services that have a high risk of freezing or solidification, wherever possible, try to avoid using these types of heat exchangers in these types of situations, since the chances of needing an entire exchanger replacement are high.

If you have to design a heat exchanger, and there is a fluid at risk of solidification,selecting the tube side for this fluid may possibly be the best choice. The tubes can be bundled and more easily replaced than the shell side. If the shell side is solid, it often results in replacing the entire exchanger.

Shell side liquids that freeze do offer the advantage of being able to use external heating to help melt the frozen matter, which may allow the exchanger to be brought back into service.

Fluids that can freeze can plug certain areas of the exchanger. This can affect the velocity within the exchanger, and affect the heat exchange and temperatures within the exchanger, which could result in the fluid setting solid. Freezing fluids, therefore, often result in large areas where the exchanger has set solid.

Shell & Tube Heat Exchanger Design

The above rules and suggestions are merely intended as guidelines to help simplify the process of choosing materials, liquids, and selecting the right sides for those liquids.

Shell and Tube heat exchanger design is a complex undertaking with various factors influencing choice of material and design. Approaching a professional organization for design, repair, and cleaning of your heat exchanger can help to ensure you have well-maintained equipment.

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How Do Heat Exchangers Work?


Conserving energy is no longer a motto. It has become an obligation for those who consume energy resources on a mass scale, such as the factories, to make sure that their energy consumption rates are at the lowest. As a matter of fact, one of the major concerns that trouble factory owners is saving energy. Conserving energy is not only costly, it is quite perplexing, since it often requires people to think outside of the box. A very simple solution to the energy conservation problem is the installation of heat exchangers.

Where Can You Find Heat Exchangers?

Heat exchangers can be found just about anywhere. Hundreds and thousands of factory owners in the world today are turning to heat exchangers to minimize the emission of heat from waste gases. It is undoubtedly one of the most useful and efficient tools to reduce energy consumption. The use of heat exchangers is not restricted to salvaging heat. It is a much more versatile device than it sounds or appears to be.

Heat exchangers are indispensable commodities in the automobile industry as well. This is because popular modes of transport, such as planes, cars, ships, and others require heat exchangers to improve the efficiency of their systems and uplift their performance. Forget about vehicles. You do not even have to look outside your home to find a use for a heat exchanger. The refrigerator or the air-conditioner in your home is making use of heat exchangers right now as you read this piece of information.

An Irreplaceable Modern Day Device

It goes without saying that heat exchangers are one of the most important devices in the modern economy. There are industries in the world that would not be able to survive, let alone thrive, in the absence of heat exchangers. The performances of home appliances such as the refrigerator and the air conditioner would have been nowhere near as good as they are today if heat exchangers were not placed inside them. Knowing exactly what heat exchangers are, the forms in which they are available, and the manner in which they work would be of great benefit to anybody, especially if one is eager to learn more about energy conservation.

Defining and Describing the Heat Exchanger

It is not always easy to define or describe devices, such as heat exchangers, mainly because of the sheer variety of their forms and the diversity of their uses. However, if we stick to using the simplest of words without digging too deeply into the details, a heat exchanger can be defined as a device or a machine which facilitates the transfer of heat from one fluid (a liquid or a gas) to another fluid, without allowing the two fluids to touch each other or experience any form of physical contact.

Central Heating System Example

It is quite impossible to conjure up a clear idea of what a heat exchanger is from a simple definition like the one mentioned above. Thus, for your convenience, the following is an example that you can relate to and use to better understand the working mechanism of a heat exchanger.

Suppose you own a central heating furnace, also known as a boiler, which heats up the hot-water radiators in a number of rooms inside your house or office. The central heating furnace kicks into action by consuming or burning natural gas. As the gas burns, a line or grid of hot gas jets fire upward, above water that is contained within a network of pipes. Although the water does not come into contact with the gas being burnt below, it is still able to absorb the heat

energy that is being dissipated from the gas by flowing through the pipes positioned above the burning gas. With increasing absorption of the heat energy, the water becomes hotter.

This entire arrangement describes how a heat exchanger works. As the name suggests, the heat is being exchanged from the burning gas (first fluid) to the water (second fluid) without creating the need for the two fluids to mix and flow into one another. Needless to say, the heating up of the water results in the cooling down of the gas jets as one fluid loses energy to the other. The end result is that the rooms inside your office or home stay warm courtesy of the heat exchanger.

Maximum Efficiency: An Objective for Heat Exchanger Manufacturers

Conserving energy is no longer a motto. It has become an obligation for those who consume energy resources on a mass scale, such as the factories, to make sure that their energy consumption rates are at the lowest. As a matter of fact, one of the major concerns that trouble factory owners is saving energy. Conserving energy is not only costly, it is quite perplexing, since it often requires people to think outside of the box. A very simple solution to the energy conservation problem is the installation of heat exchangers.

The Uses of the Heat Exchanger

As mentioned before, factories are not the only places that heat exchangers can call home. You can find heat exchangers in a number of different places, especially locations where heating or cooling or enhancing energy efficiency is a basic requirement.

Refrigerators and Air Conditioners

The most widespread use of heat exchangers is perhaps in refrigerators and air conditioners. It is interesting to note that the function of heat exchangers in air conditioners and refrigerators is quite different from the function of heat exchangers in central heating systems. In an ideal air conditioning system, the heat contained within the room is removed through the heat exchanger, and then passed on to a fluid that absorbs the heat. The heat is then dumped out of the air conditioner.

The inner working mechanism of a refrigerator is quite similar to that of an air conditioner. Instead of the heat being drawn out of a room, the heat is removed from the enclosed food compartments within the refrigerator. This causes a drop in the temperature inside the refrigerator and prevents the food from staying warm. The key element of cooling in both the appliances is the heat exchanger.

Power Plants and Engines

Power plants or engines can be responsible for energy wastage, to a great degree. In power plants or engines, you can find exhaust gases that are heated up. In other words, the heat contained within these exhaust gases is not being utilized in any way, and is being wasted as the gases are released into the open air. This is a massive waste of energy that can be easily prevented with installation of an appropriate heat exchanger. It is important to remember that heat exchangers can only reduce the amount of energy that is wasted, and not eliminate it altogether. Perfect energy conservation is only possible in theory. In practice, a certain amount of heat will always be lost, as achieving 100% efficiency is asking a little too much, even from a device as efficacious as the heat exchanger.

Working Mechanism

If you are looking to solve the problem of heat loss in power plants or engines, then you need to place the heat inside the exhaust tailpipes or smokestacks. When the engine is operating, hot gases are released, and they subsequently drift upward. For this particular operation, you need heat exchangers that are fitted in with copper fins. The purpose of the copper fins is quite simple. As the hot gases move upward, they brush past the copper fins. Within these copper fins, you have a smooth flow of water. As a result, the heat energy is passed from the hot gases to the surface of the copper fins. Copper, being a metal, is a very good conductor of heat. The heat energy is therefore transferred from the hot gases to the flowing water through the copper fins.

Heat Retrieval
& Recycling

The heat is carried away by the water back into the plant. Once the heat is returned to the plant, it can be recycled directly. One use for the retrieved heat could be warming the cold gases that are supplied to the engine or the furnace. In this way, additional energy consumption is not needed to produce sufficient heat to warm up these gases. You do not necessarily have to re-use the heat within the plant. The retrieved heat energy could very well be used to heat an office located in close proximity to the plant. This is a prime example of how a power plant can thrive on sustainable energy. Whichever the case, you will end up saving a significant amount of energy by using the heat exchanger.

Heat Exchangers in Buses

Since heat exchangers are very important to the automobile industry, a description of the uses of the heat exchanger would be incomplete without the mention of its use in automobiles. The best example of its use can be found in buses. A particular fluid is used in buses to cool down diesel engines. This cooling down is absolutely essential, since diesel engines can heatt up excessively during operation. The fluid for cooling down the engine is often passed through a heat exchanger. The retrieved heat can be used for insulation purposes within the bus.

The ventilation system of the bus is designed in such a way that the air outside the bus is pumped up from the floor of the passenger compartment. During the cold days of winter, the freezing air that is pumped up makes sitting inside the bus quite uncomfortable for passengers. One option could be to install electric heaters inside the bus. However, electric heaters are costly and consume a huge amount of energy. For a greener insulation system, the retrieved heat from the heat exchanger near the diesel engine can be used to warm the cold air that is being pumped up from the outside.

Car Radiator

Another type of heat exchanger that is worth a mention can be found inside your car. Your car radiator is actually a heat exchanger. As you must be aware, flowing water is used to cool down your car engine. After the car engine is cooled down, the flowing water becomes heated up. It is important to remove as much heat from this flowing water as possible in order to keep the car engine working efficiently. This is where the radiator, also known as the car heat exchanger, comes in. The radiator contains a number of different aluminium fins that are exposed to the air. As the car moves, the cold air outside absorbs the heat energy from the water that is contact with the aluminium fins inside the car radiator.

Similar to the bus, the waste heat of the radiator can be used to heat up the passenger compartment inside the car. The more you think about it, the more you appreciate the ingenious working mechanism of the heat exchanger.

Types of Heat Exchangers

As mentioned before, the primary working principle of all heat exchangers is more or less the same. However, there are various types or forms of heat exchangers, and each of them works in a particular way. The differences in the function of a heat exchanger are a result of the changes in the conditions in which they work. From the previous examples mentioned in this content, you can understand that the heat exchanger that is fitted inside your refrigerator cannot work inside a car and vice versa. The important thing to remember is that all heat exchangers carry out the same job of passing heat from one fluid to another. Among all the heat exchangers in use in the world today, the two most common kinds are the shell-and-tube and the plate/fin heat exchangers.

Shell-and-Tube Heat Exchanger

The shell-and-tube heat exchanger works by allowing the first fluid to flow through a number of different metal tubes. The second fluid in a shell-and-tube heat exchanger, however, takes a route through a sealed shell that encompasses the fluids. There is no definite direction in which the fluids are meant to flow. They can flow toward one another. This is known as a parallel flow. They can flow in opposite directions, known as a counter-current flow. At times, the fluids can flow at right angles. In that case, the flow is referred to as a cross flow.

Plate Heat Exchanger

A plate heat exchanger system is comprised of a lot of identical thin metal plates or fins. These metal plates or fins should have a large surface area. The larger the surface area of the metal plate or the fin is, the higher will be the rate of heat exchange. Most plate heat exchangers are designed to be lightweight, so that they can be easily placed inside vehicles such as cars, and removed when needed.

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The Effects of Heat Exchangers on Oil

The Effects

of Heat Exchangers on Oil

Heat exchangers play an important role in many cooling and heating processes. Whether they are being used in factories, power plants, car engines, or refrigerators, heat exchangers allow us to save more energy by reusing the heat from waste exhaust. But what effect do these heating and cooling processes have on the oil and equipment itself? Heat exchangers can be a useful asset to helping cool down oil lubricants and, in turn, allowing us to keep our systems running more efficiently. Choosing the correct heat exchanger and understanding the dangers of oil degradation can help keep your equipment in peak operating condition.

Types of Heat Exchangers

There are many different types of heat exchangers on the market today, and those who invest in a heat exchanger will need to take into consideration what setting the heat exchanger will be operating in, its efficiency and operating capacity, and proper maintenance of the heat exchanger.

Choosing the right heat exchanger for the job will have a large impact on the oil, and this all depends on the type of heat exchanger and what it is being used for. Some of the most common types of heat exchangers include:

Shell and Tube
Heat Exchanger:

Shell and Tube heat exchangers are popular in commercial industries due to their simple, yet durable design that involves a shell casing with a series of tubes. Fluid in the tubes is heated or cooled, while the second fluid flows over the tubes to absorb the heat. They are also popular for their ability to operate in high pressure applications. Despite being reliable, they can be somewhat inefficient compared to other models.

Double Pipe
Heat Exchanger:

As one of the simplest types of industrial heat exchangers, the double pipe heat exchanger is relatively inexpensive to build and maintain. Because of this, the double pipe heat exchanger is fairly popular with smaller companies or those with limited funds. However, they do need a large amount of space to operate and are not as efficient as other heat exchangers.

Air Cooled
Heat Exchanger:

Air cooled heat exchangers move air over the exterior of finned tubes. The tube design can play a big role in their capabilities. Aluminum finned tubes will increase the high temperature resistance properties of the heat exchanger. Air cooled heat exchangers don’t require water to operate and are therefore perfect for areas that lack water.

Heat Exchanger:

Plate heat exchangers are made up of thinner, separated plates that have fluid flow passages to assist the heat transfer. Plate heat exchangers are very space efficient and are becoming widely used due to recent advances in gasket and brazing technology.

Plate Fin
Heat Exchanger:

This type of heat exchanger uses plates and finned tubes to transfer heat between fluids. The finned tubes can be straight fins, wavy fins, or offset fins. Plate fin heat exchangers are known for being lightweight and compact, in addition to their ability to operate at lower temperatures. Because of this, they are often used in the aerospace industry. They can be difficult to clean and can be prone to fouling.

Oil Degradation Factors

There are numerous ways in which oil can degrade over time. One of the factors that plays a role in this is whether the system is open or closed. In addition to oxidative degradation, oil can also be subject to thermal degradation, additive depletion, and contamination.

Open Systems:

An open system is one that involves oil becoming exposed to the air at some point, whether it is during lower temperatures or at bulk operation. The problem occurs when oil that is not below 200 degrees Fahrenheit comes into contact with air. The system is then in danger of oxidation. This is more commonly seen in smaller applications and in industries that use portable oil heaters that are heated by electricity. Open systems are generally used well below their recommended temperatures and are not usually in danger of thermal degradation, but their design makes them increasingly susceptible to oxidative degradation.

Closed Systems:

A closed system is not in danger of oxidative degradation, as open systems are, because they have an inert gas buffer between the oil and the air, and are also not typically run above recommended temperatures. These systems are usually larger than open systems and tend to be heated by oil-fueled boilers. They are susceptible to thermal degradation due to power failures or other things outside the user’s control.


Oxidative degradation of the lubricant is the breakdown of chemical compounds by oxygen. As oxidation becomes more severe, long-chain molecules begin to assemble that produce the formation of varnish, tar, sludge, and acids. This can be seen in both open and closed systems, although it is more common in open systems.


Thermal degradation (also known as thermal cracking) is the deterioration of chemical compounds by heat that do not recombine at cool temperatures. Understanding the Arrhenius equation and how it plays into maximum bulk temperature and film temperature is crucial in order to reduce the chance of thermal degradation.

The Arrhenius Equation:

Thermal degradation of the heat transfer fluid will double for every 18 degrees Fahrenheit increase in the bulk fluid temperature. The Arrhenius equation supports the idea that a lubricant’s life is cut in half for every 18 degrees Fahrenheit increase in operating temperature. This equation (named for the 19th-century Swedish chemist, Svante Arrhenius) is a formula for the relationship between temperature and reaction rates. It is often referred to as the Arrhenius Rate Rule and determines that once lubricants have exceeded their base activation temperature, their reaction rate will double for every 18 degrees Fahrenheit increase in temperature. This increase in temperature leads to thermal degradation that can significantly impact the heat transfer fluid.

Maximum Bulk Temperature:

The highest average temperature of the heat transfer fluid is known as its maximum bulk temperature. Based off of the Arrhenius equation, thermal degradation of the heat transfer fluid will double every 18 degrees Fahrenheit increase of the bulk fluid temperature. Operating at almost 20 degrees Fahrenheit at about maximum bulk temperatures could lead to the heat transfer fluid’s life being reduced by 50 percent. Therefore, it is crucial that the temperature is lowered substantially to cut the degradation rate of the heat transfer fluid. Understanding the correct bulk temperature of the heat transfer fluid is important so that users can extend the life of the fluid.

Film Temperature:

The film temperature of a fluid is the maximum temperature a fluid is capable of in a system. It plays a role in the thermal degradation rate of the fluid and is around 50 degrees higher than the bulk fluid temperature. In most systems, one-fourth of degradation of the heat transfer fluid occurs in the film region. If the flow rate of the fluid drops while the heat remains the same, the film and bulk temperatures will rise. This will result in smaller amounts of fluid mass that is needed to remove the heat being transferred to the wall tubing. In addition, the film temperature will increase because of the decreased heat transfer efficiency, leading to the thermal degradation of the heat transfer fluid.

Understanding the correct operating bulk temperature and maximum film temperature is vital to slowing down the degradation of heat transfer fluid and maintaining the health of your lubricant. By taking the Arrhenius equation into consideration, we can assume that higher operating temperatures of oil will result in more rapid degradation. This is why investing in a heat exchanger could dramatically help slow down oil degradation.


Additives are commonly used in oil to either enhance the oil’s function or perform a function that the oil cannot. However, additives can be depleted and, once this occurs, a lubricant’s base oil must be changed even if the oil is in good condition. Additive depletion may occur at a normal rate once they perform their function, but they can deplete more quickly through contact with water or removal by particle contamination. Additive depletion can be reduced by minimizing contamination and heating oil at proper temperatures.


Contamination can degrade lubricant oils and is a common reason for the wear and tear of machines over time. Sometimes there is no way to remove contaminants from a mechanical component and the only way to combat this problem is to prevent contamination from occurring at all. This means that oil will have to be changed before contamination occurs, although there is still the chance that residual oil that is contaminated will remain in the part. It is worth it to invest in a good filtration system and ensure proper handling of the oil in order to minimize any possible contamination.

What Happens When You

Let the Oil Degrade?

It is inevitable that molecules will break down, even if you take the proper steps to prolong this process. When oil does degrade, the results of this breakdown could be damaging to the health of the heat exchanger. When oil begins to degrade, carboxylic acids starts to form and can contribute to deterioration of machine surfaces if they are left in a system long enough. The oil will become heavily oxidized, and soon begin forming varnish and sludge. The varnish and sludge can contribute to a number of other problems, such as:

  • Valve stiction
  • Filter plugging
  • Blockage of critical oil clearances

How Can a Heat Exchanger
Help Oil Degradation?

Heat exchangers transfer heat from one medium to another. They are widely used in air conditioners and refrigerators to remove heat from unwanted areas. They are also used in car radiators to help keep the radiator cool. By keeping the lubricating oil cool, heat exchangers can dramatically slow down the rate of oil degradation. You can contact trusted professionals such as Mahan’s Thermal Products to help you find the right heat exchanger for the job. Investing in a heat exchanger could be the perfect solution to stretching out the lifespan of your oil and equipment.

Other Ways to Slow
Oil Degradation


While heat exchangers are a proactive solution to the degradation of oil, there are other ways that you can slow down the degradation of oil. Following proper oil lubricating methods can provide substantial benefits. Take note of these methods of slowing oil degradation:

Keep oil as cool
as possible:

The higher the temperature, the shorter the lifespan of the oil will be. You can prolong its life by reducing the temperature of your equipment as much as you can without affecting operating procedures.

Check the manual of
the heat exchanger

Heat exchangers should come with a manual that will give you the life expectancy of fluids and maximum operating parameters. Make sure to fall within these operating parameters so that the equipment doesn’t fail.

Oil analysis:

Checking the manual may help you get a good idea of how often you should be changing your fluid, but an oil analysis can tell you more precise details. Simple things such as environment and temperature changes will make a significant difference in suggested maintenance of the oil and equipment.

Keep oil clean:

Contamination such as water, air, and dirt can increase the rate of oil degradation. Air and water both contain oxygen that can come into contact with the oil and lead to oxidation of the lubricant. Keeping your oil as clean as possible will help prolong its life.

The Impact of Heat
Exchangers on Oil

Many people are unaware of the substantial impact that heat exchangers can have on oil. There are many types of heat exchangers on the market today and investing in a heat exchanger that can cool your lubricant can provide many benefits. Oil is susceptible to problems such as thermal and oxidative degradation, contamination, and additive depletion. You can increase the lifespan of your oil by following good maintenance practices. In addition, a heat exchanger can help prolong the life of the lubricating oil by reducing the
heat within a system.

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How to Repair the Common Problems of Heat Exchanger Fouling and Corrosion


How to Repair the Common Problems of Heat Exchanger Fouling and Corrosion

Heat exchange fouling is defined as the accumulation and deposit of unwanted substances that form on the external and internal surfaces of a variety of processing equipment called heat exchangers. This nuisance material can include, but isn’t limited to, algae, scale, insoluble salts, and suspended solids.

Heat exchangers are specially designed process equipment which transfer heat semi-continuously or continuously from a hot fluid to a cold fluid, indirectly or directly, through a heat transfer surface that separates the two fluids successfully.

The major components of heat exchangers consist primarily of plate coils, tubes, and pipe bundles. When fouling forms on the surface of this process equipment, it can have a significantly negative impact on the unit’s operational efficiency.

In today’s industries, fouling can cause major economic drain. Major industry fouling costs for industrialized nations are estimated over $4.4 billion USD. This is said to be a loss of 0.25% to 30% of their GDP. It is estimated that 15% of maintenance costs are attributed by fouling. Some heat exchanger costs which are associated with fouling include:


Production loss associated with efficiency deterioration.


Production loss associated with unplanned and planned operation shutdown due to fouling.


Maintenance costs from removal of heavy fouling deposits with the use of chemicals /anti-fouling devices.


Maintenance costs associated with replacement of plugged or corroded equipment.

Cleaning costs for industries range between $40,000 to $50,000 per cleaning, per heat exchanger.

Effects of Fouling on Heat Exchangers

Fouling and corrosion can cause minor and major problems for the majority of industries who rely on heat exchangers to keep their operation running efficiently. Some major detrimental fouling effects for heat exchange units include:

  • Loss of transferred heat. This can be seen by the sudden pressure increase and temperature drop in the charge outlet.

  • Under-deposit pollution and corrosion.

  • Blocked process pipes.

Where fouling in a heat exchanger has become hot, as in steam generators, it can cause problems with the formation of local hotspots. This can result in the ultimate failure of the equipment. If an event like this occurs, it can lead to problems with increased maintenance costs and production losses. As a result, low thermal conductivity can occur due to the decrease in the charge outlet temperature combined with the thickness of the fouling layers. This results in a reduction of thermal efficiency of heat exchangers.

Common Types of Fouling

Fouling comes in many forms. Some of the most common fouling found in industries include:


– Chemical fouling is formed when there are chemical changes within the fluid. These changes cause a layer of fouling to form onto the surface of the tube equipment. One of the most common examples of chemical fouling is known as scaling. This can be seen in a boiler or kettle which is caused by the hardening salt deposits onto heating elements. When the salt solubility reduces, it can cause an overall increase in the temperature. This type of fouling can be minimized by maintaining careful control over the temperature of the tube wall that is in contact with the fluid. With the occurrence of this type of fouling, it can only be removed by mechanical de-scaling or chemical treatment processes. Some industries may use high pressure water jets, drills, or wire brushes.

– Biological fouling is generally caused by the overgrowth of different organisms within the fluid. This is then deposited onto the surface area of the heat exchanger. The type of biological fouling is typically influenced by the material choices used. One notable material that can influence the layers of fouling is that of non-ferrous brasses, which are poisonous to some organisms. When biological fouling forms, it’s normally removed by mechanical brushing processes or chemical treatments.

– Deposition fouling occurs when fluid particles settle onto the inorganic surface area. This is generally seen when the velocity of fluid falls below critical levels. This type of fouling can be helped with the proper management of the combined particles/fluids. This can be calculated to make sure minimum velocity levels are higher than critical levels. Vertically mounting the heat exchanger can also help with the minimization of fouling formation as gravity helps to pull the particles away from the heat transfer surface. This can help in low velocity levels. Deposition fouling can be removed by mechanical brushing processes.

– Corrosion fouling is when a layer of corrosion materials build up on the inorganic surface area or tubing. This creates a high thermal resistant layer of corrosion. By carefully choosing the construction materials, the effects can be minimized. For example; corrosion resistant materials, including nickel-based alloys and stainless steel, are now available to manufacturers of heat exchange units.

How to Monitor a Heat Exchanger for Signs of Fouling

Proper monitoring of a heat exchanger is crucial to maximizing refinery yield, reducing operating costs and minimizing fouling build-up. Heat exchanger monitoring is vitally important as the process is the “recycling program” of an industry. Monitoring the heat exchanger helps industries measure the heat transfer efficiency over time. Over time, the efficiency of the heat exchanger will change as fouling starts to form.

Understanding the heat transfer efficiency can help make monitoring of the system much easier in the long run. Learning the proper equations and as many parameters as possible can help keep the system running efficiently throughout its operation.

Information for Precise Heat Exchanger Monitoring

The following gives you an idea of the information that should be monitored when working with heat exchange units:

Heat Exchange Monitoring Tips

To help keep the heat exchange system running effectively, it is advisable to consider some of these simple tips:

1. Understand all available data associated with pressure, flow, and temperature indicators.

2. Find out and assess what flows, pressures, and temperatures are recorded by operators on their daily routines.

3. Continuously check the pressure. DP or differential pressure tracking on the shell side or the tube of a heat exchanger can be extremely valuable information. If the differential pressure builds up over a period of time, it means that something is restricting the flow.

4. To record any temperature data information, it is best to utilize a handheld temperature gun. Infrared temperature guns can help you monitor the temperature of the system effectively throughout its operation.

Monitoring of a heat exchanger doesn’t have to be hard. By utilizing today’s technology, along with tracking the system manually, any industry can keep track of their heat exchanger.

Fouling Mechanisms and Stages

Fouling can easily be divided into a range of different mechanisms and stages. Several fouling mechanisms generally occur at the same time, with each one requiring different techniques when it comes to prevention. With these different mechanisms, there are some of them that represent the numerous stages in the fouling process. These major fouling stages and mechanisms are as follows:

Initiation/Delay Period

This is the period of clean surface area before the fouling accumulates. Relatively small accumulations of fouling can help to improve heat transfer heat. A relatively clean surface area can help give the heat exchanger a negative fouling rate, along with a negative total fouling amount.

Particulate Fouling and Particle Formation, Flocculation, and Aggregation.


Mass Migration and Transport to Fouling Sites.


Phase Separation and Deposition

This period involves initiation or nucleation of the fouling attachment and sites leading to formation of deposit.

Growth, Hardening, and Aging of Fouling

This period sees an increase in the strength of the deposits. It also affects the erosion and removal of fouling.

• Steam Blasting

– Features the use of high pressure steam lines

• Hydro-blasting

– Features the use of high pressure water jets

Both of these techniques are designed to remove the fouling build up on the surface areas of each of the components. However, like with many other cleaning techniques, these aren’t 100% effective and successful at the removal of fouling deposits. This may leave the surface area on the components rough to the touch, even after they have been treated. Another downside is the intensity of manual labor required to dismantle and clean the heat exchanger. Having this process equipment offline for long period can cost time and money.

Chemical Cleaning of Fouling in Heat Exchanger Tubes

Chemical cleaning techniques range dramatically in the chemicals used and the results that are gained. This type of cleaning method also features many advantages which are more beneficial against mechanical repair. These advantages include:

  • Quicker cleaning process

  • Less labor intensity

  • Access to difficult to clean components that mechanical cleaning may struggle to clean

Chemical cleaning solutions provide the opportunity to clean fouling more effectively without the need to dismantle the heat exchanger. Over all, this speeds up the entire process and allows the equipment to get back up and operational in a reduced time. This can help to save time and money associated with taking the system offline for a period of time.

Basic Chemical Cleaning Process

The following steps are generally used in the chemical cleaning procedure:

1. Alkaline Clean

– Starting with an alkaline clean, this process is designed to remove the build-up of organic materials, including fats and oils, leaving the surface area of the equipment exposed and ready for treatment.

2. Rinse

– Rinsing should be done following each cleaning step. This is generally completed using a high flow water flusher. This removes any loose debris, along with any remaining residue from chemicals used.

3. Acid Cleaning

– The surface area of the equipment is then treated with the appropriately mixed acid blend. This chemical is designed to help dissolve and soften the fouling materials more successfully.

4. Rinse

– Rinsing the equipment again helps to remove any sludge, debris, or residual acid from the heat exchanger after the acid cleaning process.

5. Passivation

– The passivation process is the final stage of cleaning and is required to help add a protective coating to the surface area of the base metal components which have been exposed during the cleaning process. These areas are more vulnerable to oxidation if they are continuously exposed to open air.

Heat Exchange Repair of Division Plates from Corrosion or Fouling

Heat exchanger tube plates or division plates tend to be affected by corrosion and fouling in the same manner that tube bundles are. This damage can cause problems with inefficient performance and continuous leakages. To comply with industry standards, it’s important for these sealing faces to have a good clean finish.

Heat Exchanger Manufacturing to Combat Fouling

In the design process of a heat exchanger, fouling is taken into consideration. Generally, when they’re constructed, the manufacturer applies different methods of construction to help provide increased heat transfer in certain areas that may be affected by fouling.

Fouling tendencies all depend on the heat exchanger type and the fluids which are used. Throughout the designing stage, many manufacturers consider the following to help with minimizing the occurrence and build-up of fouling:

  • Where applicable, allocate more fouling fluid to the tube side.

  • Design the exchanger for a fouling fluid velocity of 3ft/sec on the shell side and 5ft per second on the tube side.

  • Constantly try to keep the fluid velocity regular.

  • Allow easier cleaning access of the heat exchanger.

  • In winter, don’t throttle the water flows.

  • When servicing with water, make sure the wall temperature of the tube isn’t too hot, which would create unwanted deposits of salt or render any chemicals used ineffective.

Types of Heat Exchangers

In many industries there are different heat exchangers used for different tasks. Although different, they are all very important to the proper operation and efficiency of the industry.

Shell and Tube Heat ExchangersPlate Heat ExchangerRegenerative Heat ExchangerAdiabatic Wheel Heat Exchanger

Shell and tube heat exchangers contain a combination of multiple tubes in which a constant stream of liquid flows. The tubes, which are attached to these heat exchangers, are divided into two separate sets. The first set of tubes contains liquid which is to be cooled or heated. The second set of tubes contains liquid, which triggers the exchange of heat. This liquid either removes the heat from the first set of tubes or warms it.

Plate heat exchangers generally feature thin joined plates that are maintained by a smaller rubber gasket. The plate surface area is large and features an opening which water can flow through. As the water flows over the plates, it extracts the heat and cools the liquid.

These types of heat exchangers flow fluid along both their sides through either plates or tubes. As the exiting fluid is quite hot, it is used to help warm incoming cooler water. This maintains a constant temperature within the heat exchanger.

This heat exchanger generally works when a middle fluid is used to help with heat storage. This is then transported to the other side of the exchanger via the use of a large rotating wheel. This wheel helps to transfer or extract heat within the system.


Both of these techniques are designed to remove the fouling build up on the surface areas of each of the components. However, like with many other cleaning techniques, these aren’t 100% effective and successful at the removal of fouling deposits. This may leave the surface area on the components rough to the touch, even after they have been treated. Another downside is the intensity of manual labor required to dismantle and clean the heat exchanger. Having this process equipment offline for long period can cost time and money.

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Heat Exchanger Types and Selection

Heat exchangers are commonly used devices that transfer heat from one fluid (gas or liquid) to another without those two fluids mixing. Heat exchangers play a vital role in heating or cooling facilities and helping machines run efficiently. Because heat exchangers have so many uses, they also come in manydifferent types so that they can achieve optimal performance. Knowing which type will work best for you or your business can help you achieve greater efficiency for less cost.


It is crucial to understand the range of heat exchangers in order to choose the best type to fit your specific need. There are three main types of heat exchangers: shell-and-tube heat exchangers, compact-type heat exchangers, and air-cooled heat exchangers. Each of these types has important components that allow them to work at their optimal level.


Shell and Tube Heat Exchangers

The most commonly used type of heat exchanger is the shell-and-tube heat exchanger. This type of heat exchanger is frequently used in chemical process facilities because of its ability to withstand high-pressure applications. In fact, the shell-and-tube heat exchanger industry is continually growing, and plate-fin heat exchangers took up the biggest market share in China at 54 percent. Additionally, their simple design and easy-to-service properties make them attractive choices for heating and cooling swimming pools and hydraulic fluid or oil in car engines. Shell-and-tube heat exchangers have baffles and tube enhancements that boost the performance of the heat exchanger.

Baffle Types

Baffles direct the flow of fluids through the shell side and also help support the tube so that it maintains its position. By directing the flow of fluids, baffles increase fluid velocity and efficiency. The baffle cut is the ratio of shell diameter to the baffle window height, and the baffle cut is usually around 20 percent. Baffles can be normal or parallel to the tubes and can be classified as transverse baffles or longitudinal baffles.

Transverse baffles

Transverse baffles include two types: plate baffles and rod baffles. Three types of plate baffles include segmented, double-segmented, or triple segmented baffles. The single and double segmented baffles are the most commonly used.

Segmented baffles
These have a circular disk that has a segment removed. Many shell-and-tube heat exchangers use segmented baffles.

Double segmented and triple segmented baffles
These are commonly used to reduce baffle spacing due to increasing limitations on pressure. They are categorized by their sizeable open areas and their ability to allow a flow path running parallel to the tubes. This allows for a lower pressure drop. The flow of fluid on the shell side is able to divide into two or more streams and reduce the vibration of the tubes.

No Tube In Window (NTIW) baffles
These are typically used in large components that have high flows, and which may be susceptible to flow induced vibration. The design incorporates midway supports between the baffles that increase the natural frequency between the tubes.

Expanded Metal (EM) baffles
This is made of plate material and forms an open structure that allows longitudinal flow along the shell side. This design not only improves heat transfer, but also reduces operating costs and energy consumption.

Rod baffles

The rod baffle was originally invented in an attempt to reduce flow-induced tube vibrations that could be harmful. Now they are more commonly used to increase thermal-hydraulic performance and reduce shell side fouling. Unlike plate baffles, the rod baffle design provides more effective protection of shell-side turbulence at lower pressure drops, due to their rod grids that extend on the whole shell portion. They are commonly used for gas-to-gas applications when the pressure drop on the shell side is small.


Compact Heat Exchangers

Compact heat exchangers are commonly used for applications that require an increased heat transfer rate, and are used in air conditioning systems, car radiators, and heat pumps. They are frequently used in gas-to-liquid or gas-to-gas heat exchangers to reverse the low heat transfer coefficient that may occur with gas flow within an increased surface area.

  • Plate and frame heat exchangers (gasketed, semi-welded, welded)
  • Printed circuits
  • Spiral
  • Blazed plate and frame
  •                                                               Plate-fin heat exchanger

Plate and frame heat exchangers
These use grooved metal plates that transfer heat from fluid-to-fluid. They can be gasketed, semi-welded, and welded. Plate and frame heat exchangers are frequently made from stainless steel, because of their ability to produce a large surface area, and can withstand high heat transfer between high-pressure fluids.

Spiral heat exchangers
These have a circular design and are made by taking two lengthy metal plates and rolling them around a center core until they form two spiral passages for each fluid. Spiral heat exchangers allow high heat transfer coefficients that can be 50-100 percent greater than shell-and-tube heat exchangers. They also have self-cleaning passages that reduce the effects of fouling.

Blazed plate and frame heat exchangers
These are the most compact heat exchangers on the market and, for this reason, they are frequently used for small applications rather than large commercial uses. Brazed plate and frame heat exchangers have thin stainless steel plates brazed together, which reduces the need for a frame, bolts, gaskets, and other parts. This results in a lighter heat exchanger that costs less and takes up much less space.

Plate-fin heat exchangers
These are commonly used in the aerospace industry due to their compact size and weight. These heat exchangers take thin sheets of metal and press tube holes in them, creating finned chambers that allow a relatively high heat transfer compared to their small size. Its low investment cost makes this heat exchanger attractive to many industries, including the cryogenic industry.

Printed circuit heat exchangers
These are one of the most compact heat exchangers on the market and make a great alternative to shell-and-tube heat exchangers. Flat metal plates that make up the center of the heat exchanger are arranged on top of each other and diffusion bonded. The plates form a solid metal block that allows efficient fluid flow passages. Their reduced energy costs and low fluid inventory make them attractive alternatives to conventional designs.


Air-Cooled Heat Exchangers

Air-cooled heat exchangers are used when cooling water is scarce, and they are commonly seen in hydraulic oil coolers, engine radiators, and lube oil coolers. Air-cooled heat exchangers are a great choice for those who have an alternative cooling system that may pose an economic drawback or are simply difficult to accommodate. Many places, such as Mahan’s, will help you custom design your air-cooled heat exchanger so that it will fit your specific needs. They mostly consist of finned tube bundles that help move air across them by fans.

Air-cooled heat exchangers are usually categorized by the configuration of the header. Four main types of air-cooled heat exchangers include:

Pipe and bend configuration
Plug box configuration
Cover plate configuration

Pipe and bend configuration
This uses a header of forged pipe and can handle high pressures. Pipe and bend heat exchangers can withstand very high pressures and temperatures because of its fully welded design.

Plug box configuration
This can be used for many different applications that involve cooling gases over a variety of conditions in both large and small plants. The welded box with holes in each finned tube makes it easy to inspect and clean, and it is relatively low cost.

Cover plate configuration
These are chosen for their easy to maintain design, and they have a removable cover to allow access to the inside of the header. Unfortunately, this same feature limits their ability to withstand more pressure and should be avoided in critical service applications.

A crucial aspect to air-cooled heat exchanger performance is the finning of the tubes. The three main types of finning include extruded.

Selection of Heat Exchangers

Choosing a heat exchanger can be a difficult task, and it’s important to understand the advantages and disadvantages of each type of heat exchanger. As you compare heat exchangers, it can be helpful to keep these criteria in mind:

operating Costs

installation Costs

Purchasing Costs

maintenance Costs

When you are selecting a heat exchanger, you will need to consider space limitations and other factors of your environment, as these can dramatically affect the overall cost of selecting a heat exchanger. With careful planning and consideration of the advantages and disadvantages of each heat exchanger, you can make a purchase that will increase efficiency and save you money.


Shell-and-tube heat exchangers are the most common type of heat exchanger and, for this reason, they are arguably the easiest to understand. They can be used in most process heat transfer applications and are able to withstand high pressure and temperatures. Shell-and-tube heat exchangers are incredibly versatile, and their construction allows them to endure more abuse (both physical and process).


Shell-and-tube heat exchangers are not the most economical or efficient choice of heat exchangers, especially for heat recovery purposes. This type of heat exchanger is less thermally efficient than other types of heat transfer equipment, and it is susceptible to flow-induced vibration, potentially leading to equipment failure. In addition, the shell-and-tube heat exchanger does not operate well in temperature cross conditions without multiple units in series, and it is subject to flow mal-distribution.


Compact heat exchangers have many advantages. They have a low initial purchase cost and have a variety of options to choose from, such as gasketed, semi-welded, welded, and spiral configurations. They have incredibly high heat transfer coefficients. In fact, they have three or more times greater heat transfer coefficients than shell-and-tube heat exchangers, because they have a much higher wall shear stress. Compact heat exchangers also exhibit lower fouling characteristics because of the high turbulence within the exchanger. Their true countercurrent designs allow for significant temperature crosses, and they require a small footprint for installation. They also have small volume hold-up.


Compact heat exchangers unfortunately have a more narrow range of pressures and temperatures that they can withstand and are subject to fouling because of their incredibly narrow flow path. The gasketed units require specialized opening and closing procedures, and their material construction selection is crucial because their wall thickness is so thin. process outlet temperature.


Air-cooled heat exchangers are a popular option for when cooling water is scarce or expensive to treat. In addition, air-cooled heat exchangers are great options for cooling high temperature process streams. They also are usually low maintenance and have low operating costs.


There is a high initial purchasing cost with air-cooled heat exchangers, and they require a relatively large footprint for installation. They also have a higher process outlet temperature.


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Fouling Problems: Everything You Need to Know about Prevention and Repair

Nothing in this world is perfect, and therefore nothing comes without its own set of issues that always need to be addressed.  In the industrial and commercial worlds, many people are well-acquainted with the problems facing heat exchange systems.  From leaks, reduced air flow, and vibration issues, there’s always something to deal with – although how frequently you deal with such issues depends on whether or not you rely on professional maintenance providers.  Of all of the issues that pop up with heat exchangers, though, fouling has to be the most common.

What Exactly Is Fouling?

It sounds scarier than it actually is, but fouling can still be very problematic.  It might conjure up images of foul, oozing liquids and horror-movie-quality corrosives (anyone thinking of the acid blood from the creature in Alien?) but fouling is a bit less dramatic than all of that.  It simply refers to the buildup that occurs in heat exchange systems that causes a reduction in water flow, pressure, and efficient heat exchange.  This buildup is a result of various minerals, particulates, or organic matter present in the liquid within the system.  As there are several varieties of factors that cause fouling, there are also several different types of fouling.


Also known as scaling, this type of fouling involves the crystallization of different salts and minerals within the system, often during the process of cooling.  These buildups become extremely widespread over time and are very hard, making it virtually impossible to remove them from the heat exchanger with tools without damaging any of the parts.

Sedimentation or Deposition Fouling:

With this type of fouling, various particulates present within the liquid settle and build up over time.  This type of fouling is easier to manage, as the sediments usually won’t fuse to the surface the way in which salts will in the crystallization process.  This means that if enough velocity can be maintained within the system, particulates can be kept moving.  Also, such particulates tend to break down into smaller pieces over time.  These factors mean that this type of fouling isn’t typically as widespread and is generally just concentrated in a few key areas where the flow of water has finally brought all of it to a resting point.

Organic Fouling:

Small organisms are often present in the liquids – typically water – used in the heat exchange process, and these organisms create a layer of fouling across services over time.  Usually, these organisms include various algal species, as well microbial organisms.  However, even marine organisms such as barnacles and mollusks can find their way into heat exchange systems, especially if water is being pumped from nearby natural waterways.

Chemical Fouling:

This occurs when chemicals introduced to the system react with the metal present and cause the formation of a layer of buildup.  This is somewhat similar to the crystallization process, but whereas with that process the fouling is due to a scale deposit related to the buildup of crystalized salts, this process produces a scaling entirely based on chemical reactions.

Corrosion Fouling:

All of the aforementioned fouling processes can lead to corrosion, but in those instances the corrosion is a secondary element to the original fouling process.  With corrosion fouling, the immediate process is corrosion, often caused by high acidity levels or chemical imbalances.  This commonly leads to major rusting throughout the system; something that can easily lead to an entire system break down.

Common Control and Cleanup Methods:

It’s extremely important to respond to fouling as soon as possible, so the best means of protecting your heat exchange system is to schedule regular maintenance and cleaning with a professional service, such as Mahan’s Thermal Products.  Another means of combating the fouling process starts before the heat exchange system is even built and installed.  Carefully designed systems can be engineered to create environments that are far less conducive to fouling processes, either by creating a system that maintains a certain velocity, or by including materials or substances that actively inhibit certain types of fouling.

For example, copper will create an environment that is poisonous to organisms that contribute to the biological fouling process.  Chlorine can also be added to the liquid within the system in order to prevent/inhibit biological growth.

In terms of cleanup, fouling processes that create hard scale buildups can only be thoroughly cleaned with the use of chemicals.  Scale caused by chemical fouling can sometimes be cleaned manually with special brushes, but crystallization can really only be dealt with through the use of a chemical cleaner.  Particulates can be removed manually and filters can be installed in order to prevent or drastically limit the amount of particulates capable of entering the system.

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Shell and Tube Heat Exchangers: Pros and Cons

Heating and cooling needs aren’t quite as straightforward in the industrial and commercial sectors as they are in residential situations.  Whether heating a space or cooling machinery, heat exchangers have to perform at exceptional rates and need to be as efficient and cost-effective as possible.  One of the most common types of heat exchangers is the shell and tube heat exchanger, and here you’ll find out about the different types of shell and tube heat exchangers, their functions, and the pros and cons of this form of heat exchanger.

Types and Functions:

The general function of all shell and tube heat exchangers is to transfer heat from one liquid to another.  The exchanger performs this function by acting as a container where heated liquid can enter through pipes, where it’s passed over by cooler liquid.  Within the exchanger, heat is transferred from the hot water pipes to the cold water.  This allows for two functions: the return of formerly heated water to machinery where, now cooled, it can pull excess heat from in order to cool the machinery; or the formerly cold water can circulate back to a space where it can now, in heated form, warm the space.

Two common types of shell and tube heat exchangers are u-tube and straight-tube exchangers.  In a u-tube system, pipes enter at one end and bend into a u-shape at the other in order to exit back at the same end they entered from.  Liquid is passed through the heat exchanger on one end and exits out the other in order to remove or introduce heat to the pipes.  For a straight-tube system, the pipes enter the heat exchanger at one end and exit at the other.


No matter the type or configuration of shell and tube heat exchanger, all of them utilize baffles.  Baffles are essential for optimizing heat transfer, and, without them, the system would not only work less efficiently, but would also be more susceptible to damage.  These components control how water circulates over the pipes that enter the heat exchanger and can be implemented in three different ways: single segmental; double segmental; and disc and doughnut.

Single segmental baffles create an up and down movement of water over the pipes in the exchanger.  Double segmental baffles also create an up and down movement, but it’s in a counter flow pattern, whereas in the single segmental system water moves up, then down, then up, and so on. In the double segmental system, water flows up and down in the same motion, flowing up and down away, and then up and down head-on.  With disc and doughnut baffles, water is forced to move in a circular motion over the pipes.

The baffles come in different designs not because there are conflicting beliefs about which works best for all heat exchangers, but because different baffle designs work better depending on the temperature and pressure present in the system.  Understanding these ratios allows engineers to determine which arrangement will yield the best exchange of heat within the system.

Pros and Cons of Shell and Tube Heat Exchangers:

Pros – These exchangers are less expensive to install than other varieties – such as plate heat exchangers – and offer more versatility in terms of temperature and pressure endurance.  They can also be repaired more easily than other types of heat exchangers, as it’s easier to ascertain where a leak is and easier to repair it.

Since this type of heat exchanger is so common, it’s easy to find a professional service that not only can properly install the system, but can also properly clean and repair it on a regular basis.  This reduces the likelihood that crucial components of the system will be overlooked or mishandled, leading to costly damages or even workplace injury.

Cons – These exchanger systems are susceptible to vibration problems, caused by the water flowing through the pipes.  However, the baffles are meant to hold pipes in place and reduce the effects of vibrations.  They’re also not as efficient at other models in terms of heat exchange and heat yield.

Some corrosion issues are also possible with this type of exchanger, mostly due to the fact that it contains inactive zones where water is able to pool and remain relatively stationary.  One of the biggest cons to this system, though, has to do with the size of the heat exchanger.  Compared to other heat exchangers, tube and shell heat exchangers take up more space and are therefore bulkier.

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Cooling Towers: Types, Functions, and Why They’re for You

Whenever anyone hears the term, “cooling tower,” more than likely the first image that springs to mind is that of a nuclear power plant, with the tall, cylindrical towers that widen at the base.  Cooling towers are used in far more processes than just nuclear energy, though.  Industrial facilities all over the world utilize various types of cooling towers as part of their cooling systems.  These towers and the systems they’re attached to work to transfer heat from important machinery and disperse it elsewhere, thus ensuring that nothing overheats and therefore malfunctions – a possibly dangerous scenario.

The Various Options:

Cooling towers come in a variety of designs and implement a variety of cooling processes.  This is due to the fact that, depending on the climate of an area, certain types of cooling towers function better than others.  Temperature, humidity, and even precipitation levels are all factors to take into consideration when opting to install a cooling tower.

Two common types of cooling towers are crossflow cooling towers and counterflow cooling towers.  They both operate according to the same general principle; it’s just the way in which they implement this principle that’s different.  Both work with a system in which hot water is introduced to the cooling tower in order to interact with air, and thus transfer heat and cool the water.  With a crossflow tower, water works its way down a filler – typically some type of PVC material – where air is blown perpendicular to the flow of water.  In a counterflow tower, water and air meet each other head on, with water typically moving downward and the air moving upward.  With counterflow systems, there typically isn’t any type of filler.  Instead, water drops through open air or even sometimes a system of plates, and then open air.

A forced draft tower typically operates in a counterflow process.  In this system, air enters the tower at the base where it passes through a blower and is forced upwards.  Water is sprayed from the top and, in this system, often passes through a filler, such as a series of metal plates.  As the air passes over the water and through the plates, it carries the heat with it in the form of evaporates and is discharged into the atmosphere at the top of the tower.

Natural draft spray towers use a cross flow method where air is drawn in and passes a stream of water sprayed from above.  As with a forced draft tower, the cooled water falls to the base of the tower where it settles in a basin before being pumped back to whatever equipment or machinery it’s being used to cool.  These towers are often preferred to forced draft towers because they’re quieter, relying on natural air flow rather than noisy fans.

Sometimes more control is desired over the water that’s circulating through a cooling system.  In a closed circuit system, the water used to cool machinery doesn’t leave the system and therefore is not introduced to external elements.  This is beneficial because it reduces the likelihood of external elements introducing anything that may make the water more acidic – and therefore corrosive – and it helps cut down on fouling.

Such closed systems utilize a fluid cooler tower.  In this tower, water used for cooling is brought in by pipes which circulate down through the tower, kind of like a filler.  Separate water stored in the tower is sprayed down through the tower and over the piping, which acts as a heat exchanger, while air is forced up from the base through a blower.  The spray water collects the heat from the pipes, and then descends through the blown air, which in turn takes the heat and discharges it through the top of the tower.

Is the Investment Worth It?

Some cooling towers aren’t that expensive to purchase and install.  In fact, a variety of smaller cooling towers are often used in a variety of commercial and industrial settings.  Larger cooling towers, all the way up the tall stacks commonly seen at nuclear and hydroelectric power plants, are obviously larger investments, but they’re worth it.  Cooling towers are typically far more efficient than other means of cooling, requiring less energy and therefore less money to operate.

Many cooling towers, such as those that utilize natural draft systems, require very little maintenance because they don’t have any moving parts and aren’t very complex systems.  For sustainability purposes, cooling towers are great because they cut down or even eliminate the need to use fossil fuels for the same process.  Many rave about natural gas, and while it may burn “cleaner” than other fossil fuels, it’s still a finite resource and can be very expensive.  For efficiency, sustainability, and cost-effectiveness, cooling towers are still the way to go.

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Hexavalent Chromium: A Groundwater Contamination Dilemma

In a modern, industrialized first-world country, the simple act of turning on a faucet and filling a glass, a pitcher, or a pot with water isn’t an action that typically comes with a lot of analysis.  For most, it’s like a second-nature process: You need water, you get water, and you move on.  However, all across America – as with many other first-world nations – water contamination is becoming an increasingly problematic issue.  Ever heard of hexavalent chromium?  Well, there’s a good chance that you’re at least familiar with the film, Erin Brockovich, which catapulted it into mainstream awareness.  Whereas the movie is a Hollywood depiction of a single contamination that took place in Hinkley, California, contamination of groundwater with hexavalent chromium is something that’s become more of a news staple, rather than a box office dramatization.

What’s the Issue Here?

The big question surrounding this issue is, of course, why is this a serious problem?  What’s up with hexavalent chromium?  For starters, it’s extremely toxic.  When inhaled – something most likely to happen in the case of industrial workers – it can inevitably lead to lung cancer and other respiratory ailments.  When it reaches groundwater sources and is subsequently ingested, it can lead to a variety of cancers – most commonly stomach and gastrointestinal cancers – as well as ulcers, kidney and liver failure, and more.  Children are particularly susceptible to the effects of hexavalent chromium, putting them at much higher risk for developing any of these medical conditions due to exposure to the toxin.

Key Contaminators:

So now you’re probably wondering, who’s even using this stuff in the first place?  Well, plenty of industrial plants, for one.  Hexavalent chromium is commonly used as an anti-corrosion agent, usually in industrial cooling systems.  Industrial and manufacturing facilities often rely on a heat exchanger system or cooling towers that circulate water through a system of pipes in order to draw heat away from machinery and equipment.  The water alone can lead to corrosion over time, especially if it happens to be slightly more acidic, but various chemicals are often added to the water in order to enhance the cooling process or to help break down mineral and bacterial buildups in the system, something that can also add to the corrosive property of the water.  The hexavalent chromium is therefore added in order to undermine any corrosive properties found in the water.

Other industrial practices create or use chromium due to completely different processes.  It’s a common feature in various leather tanning enterprises, as well as welding industries, textiles (dyes), and wood preservation.  Whether as an additive or as a by-product, hexavalent chromium pops up in all of these industries and, if not handled properly, can easily find its water in groundwater supplies.  This is precisely why it’s important for heat exchanger systems to be regularly cleaned and repaired, and for professionals to be consulted in order to find other options besides hexavalent chromium that can help combat corrosion.

Contamination and Clean Up:

Hinkley, California, isn’t the only city in America where hexavalent chromium has been found in drinking water.  At least 31 cities across the country have been shown to contain the toxic chemical, but the EPA hasn’t taken action because the levels are well below their maximum limit of 100 ppb (parts per billion).  The issue with that cutoff number is that it measures total chromium content, which includes other chromium chemicals that aren’t a health risk to people.  California has seen the most research and experimentation done regarding hexavalent chromium, with scientists deciding that anywhere from .02 ppb to .07 ppb would be the maximum acceptable values for human consumption.

Groundwater contamination continues to be a problem across the country, with plumes of the chemical spreading throughout aquifers, and therefore polluting more and more drinking water.  Various sites in California have popped up, as well as in New Mexico, Texas, Massachusetts, and Illinois, among others.  Groundwater contamination is extremely hard to combat though, as once chemicals and toxins enter an aquifer it’s difficult to stop them from flowing through it.  Clean up processes include pumping up groundwater and treating it in order to remove the toxins, or added non-harmful substances to the groundwater meant to interact with the toxins and cause them to break down into non-harmful elements.

A major stumbling block, however, are the limits being set for how much hexavalent chromium is allowed in drinking water? With the EPA yet to set a clear mandate specifically regarding hexavalent chromium, it’s likely that carcinogenic levels of the toxic chemical will remain in the drinking water of many communities.  Reliable supplies of freshwater are crucial for both residential and agricultural use, and, unless further change can be enacted regarding the safety of groundwater, we’re likely to see further problems down the road.

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