A two-shell passes and four-tube passes heat exchanger is used for heating a hydrocarbon stream (c_p = 2.0 kJ/kg·K) steadily from 20°C to 50°C. A water stream enters the shellside at 80°C and leaves at 40°C. There are 160 thin-walled tubes, each with a diameter of 2.0 cm and length of 1.5 m. The tube-side and shell-side heat transfer coefficients are 1.6 and 2.5 kW/m²·K, respectively.

(a) Calculate the rate of heat transfer and the mass rates of water and hydrocarbon streams.

(b) With usage, the outlet hydrocarbon-stream temperature was found to decrease by 5°C due to the deposition of solids on the tube surface. Estimate the magnitude of fouling factor.