Designing a test heat exchanger

As the physical layout of the exchanger cannot be determined until the area is known the design of an exchanger is of necessity a trial and error procedure. The steps in a typical design procedure are given below:

1. Define the duty: heat transfer rate, fluid flow-rates, temperatures.
2. Collect together the fluid physical properties required: density, viscosity, thermal conductivity.
3. Decide on the type of exchanger to be used.
4. Select a value for the overall coefficient, U.
5. Calculate the mean temperature difference, Δtm .
6. Calculate the area required from equation Q = UA Δtm
7. Decide the exchanger layout.
8. Calculate the individual coefficients.
9. Calculate the U and compare it with selected U value. If the calculated value differs significantly then return to step 6.
10. Optimize the design: repeat steps 4 to 10, as necessary, to determine the cheapest exchanger that will satisfy the duty. Usually that will be one with the smallest area.

Typical values of the overall heat-transfer coefficient for various types of heat exchanger are given below: