There is no denying the fact that heat exchangers are one of the most important pieces of equipment in the industrial sector. They also have numerous applications in the commercial and residential sector, which makes them one of the greatest inventions in the history of modern human civilization.
Heat exchangers are available in a variety of sizes. For example, a cold plate heat exchanger can be fitted inside a cell phone, while a waste heat recovery system is often seen occupying large amounts of space in a plant.
There is also a great deal of variety in terms of shape. For instance, the shape of a shell and heat tube exchanger does not resemble the shape of a plate and frame heat exchanger in any way.
Distinctions can also be made based on the function of the equipment. For example, you have two kinds of heat exchangers being sold on the market: the recuperative heat exchanger and the regenerative heat exchanger.
The Constant Need for Development
Heat exchangers have evolved quite considerably over the years. Hundreds of developments have been made to heat exchanger systems in order to improve their performance and enhance their durability. People have been studying, analyzing, and optimizing heat exchangers for a fairly long period of time. All of this is being done to reduce the capital and running costs and to increase the overall efficiency of the system.
However, despite the fact that people have made tremendous progress in developing heat exchangers, it is quite unlikely that the effort to increase the performance and durability of heat exchangers will ever come to an end. In other words, you will continue to read and learn about new developments being made to heat exchangers every single year. This evolution is the gift of technology.
An Engineering Problem
Designing or selecting a heat exchanger can be viewed as purely an engineering problem. As is the case with most engineering problems, this requires a balance between capital and operating costs. Capital cost of the heat exchanger is based on the amount of heat transfer area that the system has on offer. The larger the area, the greater will be the transport of heat between the hot and cold medium. Larger/heavier heat exchangers are more expensive than the smaller/lighter ones.
In most cases, the cost of the heat exchanger is also heavily reliant on the construction material that has been used. If expensive materials are used during the production process, such as those that have exceptional conducting attributes and temperature/corrosion resistant properties, then you can expect the initial costs to be higher.
On the other hand, you have the running cost or the operating cost of heat exchangers. This can be based on the bumping power, the maintenance cost, the cleaning cost, and even the replacement cost.
Major Problems with Heat Exchangers
It is worth mentioning that Exhaust Gas Recirculation (EGR) coolers are used in a number of different diesel engine vehicles. These are one of the most fragile components of the engine vehicle. The reason why it is fragile is because it is exposed to extremely hot exhaust gases. In certain cases, the temperature can reach as high as 1000 degrees Celsius.
These gases are not evenly distributed. They get non-uniformly distributed to a variety of tubes as the gas releases heat energy. Because of this non-uniform distribution of hot exhaust gases, the tubes undergo uneven heating and cooling. This ultimately gives rise to a variable thermal strain. This leads to excessive stress on the end plates that keep the tube bank in position.
In addition to this problem, you have the issue of variations in the temperature and flow rate of the incoming gas. These changes are mainly based on the engine load condition that leads to cyclic thermal load on the EGR cooler.
Furthermore, there are times when clogging of the coolant channel leads to overheating of the coolant. This often causes aggravated heating of the tubes and leads to excessive localized stress. Last, but not the least, fouling (carbon deposits) on the tube walls can significantly damage the heat exchanger.
Simulations are often used to analyze the problems that have been mentioned above. Shape optimization studies are conducted to restructure the design of the inlet header so that uniform distribution of the incoming gas can be ensured. Phase change simulations are also carried out to predict boiling and condensation in coolers.