In current service, 20 kg s- cooling water at 12C must be circulated through a coil inside a fermenter to maintain the temperature at 37C. The coil is 150 m long with pipe diam- eter 12 cm; the exit water temperature is 28C. After the inner and outer surfaces of the coil are cleaned it is found that only 13 kg s-1 cooling water is required to control the fermenta- tion temperature. (a) Calculate the overall heat-transfer coefficient before clean- ing. (b) What is the outlet water temperature after cleaning? (c) What fraction of the total resistance to heat transfer before cleaning was due to fouling deposits?