The calculations carried out to design heat exchangers are far from exact. In fact Perry’s refers to the design of heat exchangers as being an art as much as a science.
These days almost all heat exchanger designs are carried out using software specifically written for the purpose. The most accepted software used for heat exchanger design is that produced by Heat Transfer Research Inc. (HTRI). Although this, and other company’s software are invaluable in carrying out the actual calculations they are limited in their ability to give guidance to the designer as to what is the best exchanger type, fluid placement and orientation for the particular design being considered.
Therefore, the designer must have a good understanding of where to start and how to adjust the various parameters to achieve the optimum design. Even when using design software, the heat exchanger design procedure (often called rating) is iterative. The procedure is illustrated on the following flowchart. Basically, the procedure is to choose a design and then test the selected design against the requirements. If the design meets the requirements in all respects the design is complete. If the design does not meet some or all of the requirements then the design is adjusted and the procedure repeated.