In the mechanics, a heat exchanger is defined as a system that can be used to transfer heat between two or more fluid substances, which may be separated by solid walls to prevent mixing, or they may be in direct contact with each other. In general, they are widely used in space heating, refrigeration, air conditioning, power stations, petrochemical plants and refineries, natural gas processing, and some other system such as sewage treatment.
Traditional examples of heat exchangers have been found in internal combustion engines. In this example, there is a circulating fluid, called the engine coolant. It flows through the radiator coil and the air flows through the coil, which cools the coolant and heats the incoming air as designed. Another example is the radiator. This is a passive heat exchanger that can transfer heat generated by electronic or mechanical equipment to a liquid medium or liquid coolant, usually air.
Regarding the classification of heat exchangers, there are many types within this category. A common example is the double pipe heat exchanger, which is the simplest heat exchanger design and is used for multiple purposes in industry. On the one hand, considering the design and maintenance stage, the price of this heat exchanger is relatively cheap, so these essences make it a good choice for small industrial users.
On the other hand, the low efficiency of the double pipe heat exchange, coupled with the large amount of space occupied by these two areas, has led modern industrial users to use more efficient heat exchangers for convenience, such as the shell and tube or plate designs. Because the structure of the double tube heat exchanger is quite simple, they are used to teach students the basis of heat exchanger design due to almost the same basic rules of all heat exchangers.
For more advanced designs, the shell and tube heat exchangers usually consist of a series of excellent tubes that contain fluid substances that must be heated or cooled as engineering requirements. In addition, the second fluid flows through the arranged heated or cooled tubes and provide heat or absorb heat required for the functionality. In this system, a set of tubes is called a tube bundle, and they can be composed of multiple tubes, such as plain, longitudinally finned, and others. The shell and tube heat exchangers are commonly used in high pressure applications with pressures greater than 30 bars and temperature levels greater than 260 degrees C. These two types of heat exchange mechanisms are widely used due to their respective advantages. Industrial users can choose which one to apply based on their factory specifications, such as location, space, and many other conditions.
Inside the heat exchanging engineering, the waste heat recovery unit is also abbreviated as WHRU, which is a heat exchanger that can recover heat from the hot gas stream and transfer it to the working medium. The medium is usually a common substance, such as water or oil. In fact, the hot gas stream can be exhaust gas from a gas turbine or diesel engine, or it can be exhaust gas from industry or refinery usages.
For large systems designed for high volume and high temperature gas stream in industry, they can benefit from SRC, which is an abbreviation for (Steam Rankine Cycle) in waste heat recovery units. If these systems cost too much, this is suitable for small system. In addition, the recovery of heat from low temperature systems requires a different working fluid substance than steam. The rearrangement and design of the entire system requires professional experts to participate in the field. Compared with the system we just introduced, ORC, Organic Rankine Cycle, waste heat recovery device is more effective in the low temperature range using a refrigerant with a lower boiling temperature than water.
With a simple comparison and the application shown, we can have a conclusion that in sum. In the field of heat exchange, neither type has an absolute advantage, but depends entirely on the working conditions and circumstances.
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