Detailed Analysis of a Double-Pipe Heat Exchanger

A rigorous analysis was performed on heat exchanger E-408—the goal being to determine an overall heat transfer coefficient, U, as well an effective heat transfer area, A. Hysys provides a total UA value making it necessary to use a different method to find U and A separately. First, a heat balance was done on the two streams to verify the heat flow, Q, value given by Hysys. The calculated heat flow and that given in Hysys were within a reasonable error. Assuming that there is counterflow, a log-mean temperature difference coefficient was found to be 30.16 ° C, which also checks with the value given by Hysys. By industry standards, the cold stream was chosen to flow through the inner pipe; this is because the inner pipe has the larger flow area and the cold stream in this case is the larger stream. A calculated flow area of 0.018 m² was found for the inner pipe while a flow area for the annulus was 0.031 m². Viscosity data for each of the streams were taken from Hysys, which allowed for the calculation of Reynolds numbers.

Both of the Reynolds numbers were approximately 4000 indicating that turbulent flow was occurring, which is reasonable for the process. Next heat-transfer coefficients were estimated using the Reynolds numbers and tube-side heat-transfer curves. An inside heat-transfer coefficient was found and then transformed into that for the outside. Using these two values an overall heat-transfer coefficient was calculated to be 304 W/hr*m²* ^° C, while a heat transfer area of 17.14 m². Compared to the values given by Turton, Bailie, Whiting and Shaeiwitz in Table 9.11 of 350 W/ m^2° C and an effective exchange area of 9.3-18.6 m² the calculated values are within reason. See Appendix for equations used in calculations and a table of determined values.