A double-pipe, countercurrent heat exchanger is used to cool a hot liquid stream of biodiesel from 60°C to 35°C. Biodiesel flows on the shell side with a volumetric flow rate of 3 m³/h; water is used on the tube side. The entrance and exit temperatures for cooling water flow are 10°C and 30°C, respectively. The inside diameter of the schedule 80, 1.5 in. copper tube used within the heat exchanger is 1.5 inch (3.81 cm). In independent experiments, the heat-transfer coefficient for bio- diesel on the shell side was determined to be 340 W/m² · K. Since the tube wall is made of copper, thermal conduction resistances can be neglected. Average properties of liquid biodiesel (B) from 35–60°C are: ρ_B = 880 kg/m³, µ_B = 4.2 × 10^-3 kg/m-s, k_B = 0.15 W/m · K, C_p,B = 2400J/kg · K. 

a. What is the heat load on the heat exchanger, and what mass flow rate of cooling water is required? 

b. What is the required heat-exchanger surface area? 

c. What would be the required heat exchanger for co-current flow’?