Assume that the oil in problem P.7.1 is an organic liquid coming from a chemical reactor. It is necessary to “quench” this hot oil as quickly as possible to stop the reaction and prevent its degradation into a useless byproduct.

(a) Would you use a counter-current or a co-current configuration in your double-pipe heat exchanger? Plot T vs. Q to explain your answer.

(b) Suggest a type of heat exchanger that might be better than a double-pipe for this quenching operation.

Data From Problem P.7.1:

A double-pipe heat exchanger is to be designed to cool 5.5 gal/min of a hot oil from 250°F to 120°F using 11 gal/min of cooling water available at 70°F. The exchanger is to consist of 12-ft-long sections of ¾-in.-diameter copper tubing placed inside 1½-in.-diameter, well-insulated tubing, with water flowing in the annular space between the two tubes. 

The overall heat transfer coefficient is U_° = 110 BTU/h ft² °F, the heat capacity of the oil is 0.55 BTU/lb °F, and the density of the oil is 52 lb/ft³. Assume that there is no heat transfer to the surrounding.