Consider the exchanger in Problem 22.9. After 4 years of operation, the outlet of the oil reaches 28°C instead of 30°C with all other conditions remaining the same. Determine the fouling resistance on the oil side of the exchanger.

Data From Problem 22.9

A shell-and-tube heat exchanger is used for the heating of oil from 20°C to 30°C ; the oil flow rate is 12 kg/s (C_po = 2.2 kJ/kg · K). The heat exchanger has one shell pass and two tube passes. Hot water (C_pw = 4.18 kJ/kg · K) enters the shell at 75°C and leaves the shell at 55°C. The overall heat-transfer coefficient based on the outside surface of the tubes is estimated to be 1080 W/m² · K.