For the heat exchanger described in Problem 22.27, it is observed, after a long period of operation, that the cold stream leaves at 184°F instead of at the design value of 220°F. This is for the same flow rates and entering temperatures of both streams. Evaluate the fouling factor that exists at the new conditions.

Data From Problem 22.27

A shell-and-tube heat exchanger with two shell passes and four tube passes is used to exchange energy between two pressurized water streams. One stream flowing at 5000 lb_m/h is heated from 75 to 220°F. The hot stream flows at 2400 lb_m/h and enters at 400°F. If the overall heat transfer coefficient is 300 W/m² · K, determine the required surface area.