As was discussed before, heat exchanger are equipment used for heat transfer between two fluid flows with different temperatures. In design of heat exchangers such as double pipe heat exchanger, shell & tube heat exchanger, etc., it must be noted that there are some factors that affect the heat transfer rate during the equipment operation period. One of the most important factors is called fouling.
In the 2nd part of this article, the calculation of convective heat transfer coefficient was explained. In a double pipe heat exchanger the internal and external heat transfer coefficients are different and it is required to use an overall heat transfer coefficient to perform the calculations.
As was mentioned before, UC, is defined as follows based on convection heat transfer coefficients:
Double pipe heat exchangers are the simplest exchangers used in industries. On one hand, these heat exchangers have low cost for both design and maintenance, making them a good choice for small industries. But on the other hand, low efficiency of these exchangers beside high space occupied for such exchangers in large scales, has led modern industries to use more efficient heat exchanger like shell and tube or other modern heat exchangers. But yet, since double pipe heat exchangers are simple, they are used to teach heat exchanger design basic to students and as the basic rules for modern and normal heat exchangers are the same, students can understand the design techniques much easier.
Heat exchangers (HEX) are one of the most important parts of industries like chemical, medical, or many other industries. These systems are used to transfer or “exchange” thermal energy (heat) between two fluids which can be gas or liquid. Heat exchangers can be found in different types such as double pipe, shell & tube, spiral tube, plate, etc. but the two first types are and specially shell & tube exchangers are more common in industries.