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Q: A counter flow, concentric tube heat exchanger used for engine cooling has been in service for an extended period of time. The heat transfer surface area of the exchanger is 5 m2, and the design value of the overall convection coefficient is 38 W/m2 · K. During a test run, engine oil flowing at 0.1 kg/s is cooled from 110°C to 66°C by water supplied at a temperature of 25°C and a flow rate of 0.2 kg/so Determine whether fouling has occurred during the service period. If so calculate the fouling factor, R''f (m2 · K/W).