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 first part of this article, heat exchanger design basics were introduced. In the following article, the design formulations and calculations are introduced.
As mentioned in part 1, overall heat transfer in heat exchanger in increased in the flow are set to be countercurrent. As a result, only countercurrent double pipe heat exchanger design is discussed here. To start the design of a double pipe heat exchanger, the first step is to calculate the heat duty of the heat exchanger. It must be noted that for easier design, it’s better to ignore heat loss in heat exchanger for primary design. The heat duty can be defined as the heat gained by cold fluid which is equal to the heat loss of the hot fluid. It can be calculated as:
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.