A 10 m long countercurrent-flow heat exchanger is being used to heat a liquid food from 20 to 80°C. The heating medium is oil, which enters the heat exchanger at 150°C and exits at 60°C. The specific...

A 10 m long countercurrent-flow heat exchanger is being used to heat a liquid food from 20 to 80°C. The heating medium is oil, which enters the heat exchanger at 150°C and exits at 60°C. The specific heat of the liquid food is 3.9 kJ/(kg K). The overall heat-transfer coeffi cient based on the inside area is 1000 W/( m
²
K). The inner diameter of the inside pipe is 7 cm.

a. Estimate the flow rate of the liquid food.

b. Determine the flow rate of the liquid food if the heat exchanger is operated in a concurrent-flow mode for the same conditions of temperatures at the inlet and exit from the heat exchanger.