5.38 A 2 DPHX is made from sch 40S stainless steel. Acetone enters the heat...

5.38 A 2 × ¾ DPHX is made from sch 40S stainless steel. Acetone enters the heat exchanger at 80°F with a volumetric flow rate of 12 gpm. The other fluid, ethanol, enters the heat exchanger with 10°F with a flow rate of 45 gpm. The required heat exchanger duty (heat transfer rate between the two fluids) is 75,000 Btu/h. The thermal conductivity of the stainless steel tube can be taken as 8.1 Btu/h·ft·°F. The counterflow arrangement will be used to minimize the heat exchanger area required. The footprint for this heat exchanger only allows for a maximum horizontal, straight length of 8 ft.

a. Which fluid should be placed in the annulus? Which fluid should be placed in the tube? Justify your answer with calculations.

b. How many straight, horizontal DPHX must be hairpinned together to meet the heat exchanger duty?

c. Calculate the outlet temperatures of each fluid and the heat exchanger duty when the heat exchanger is first placed in service and it is clean.

d. Calculate the outlet temperatures of each fluid and the heat exchanger duty after the heat exchanger has been in service for 1 year.

e. What are the pressure drops (psi) of each fluid in the heat exchanger?