4. (1 pt) Heating of a Product in Parallel Flow or Counterflow Heat Exchanger: NTU Method

Consider a concentric-tube heat exchanger that is 3 m in length. The inside diameter of the inner tube is

0.01 m and the inside diameter of the outer tube is 0.02 m. The wall thickness of the inner tube can be

neglected. A fluid enters the inner tube at 10 °C and flows at an average velocity of 0.3 m/s. Water enters

the annular region between the tubes at 50 °C and flows at an average velocity of 0.1 m/s. The overall heat-

transfer coefficient is 350 W/m²-K. Properties of the fluid: p = 1300 kg/m³, c = 2500 J/kgK. Properties

of water: p = 1000 kg/m³, c = 4200 J/kgK. Using the NTU method, determine the temperature of the

fluid exiting the tube if:

A. It is a counterflow heat exchanger.

B. It is a parallel-flow heat exchanger.

C. Which type of heat exchanger provides a higher heat-transfer rate and by what %?