Shell-and-tube heat exchanger is used to cool oil (ch 2.2 kj/kg ? k) from 110°c to 65°c. the heat exchanger has two shell passes and four tube passes. the coolant (cc 4.20 kj/kg ? k) enters the shell at 20°c and leaves the shell at 42°c. for an overall tube-side heat-transfer coefficient of 1200 w/m2 ? k and an oil flow of 11 kg/s, determine a. the coolant mass flow rate b. the required surface area in the exchanger