A thin-walled concentric tube heat exchanger is used to cool engine oil from 175 °C to 55 °C with water that is available at 27 °C acting as a coolant. The oil and water flow rates are each 2.5 kg/s and the diameter of the inner tube is 0.7 m with a corresponding value of overall heat transfer coefficient of 223 W/m2-K. The specific heat (cp) of the engine oil is 2.035 kJ/kg-K.
a. What is the outlet temperature of the water in °C?
b. Based on your answer above, determine the type of heat exchanger, i.e. parallel flow or counter flow.
c. What is the rate of heat transferred (kW) from the oil to the water?
d. How long must the heat exchanger be to accomplish the desired cooling?