A shell and tube heat exchanger is being used to cool 150,000 lbm/h of benzene in a detergent manufacturing process. The benzene enters the heat exchanger at 125°F and its outlet temperature must not exceed 90°F. City water, flowing at 180,000 lbm/h enters the heat exchanger at 65°F to provide the required cooling.
The heat exchanger is a single shell 2-tube pass configuration with a 17¼ inch shell. The tubes are ¾-in 18 BWG on a 1-in triangular pitch. The heat exchanger is 16 ft long and contains 10 baffles. The benzene is routed through the tubes and the water flows in the shell. If maintenance does not occur on the heat exchanger until a year of service is complete, determine the

a. Benzene and water outlet temperatures

b. Pressure drops for each of the fluids (psi)

c. If the benzene outlet temperature calculated in Part (a) is higher than the maximum allowed temperature of 90°F, what maintenance period would you recommend (months between cleanings)? Assume that the fouling occurs linearly in time.

d. What is the benzene outlet temperature for the maintenance period suggested in Part (c)?