# Hot water (cph = 4188 J/kg·K) with mass flow rate of 2.5 kg/s at 100°C enters a thin-walled concentric tube counter-flow heat exchanger with a surface area of 23 m2 and an overall heat transfer coefficient of 1000 W/m2·K. Cold water (cpc = 4178 J/kg·K) with mass flow rate of 5 kg/s enters the heat exchanger at 20°C, determine (a) the heat transfer rate for the heat exchanger and (b) the outlet temperatures of the cold and hot fluids. After a period of operation, the overall heat transfer coefficient is reduced to 500 W/m2·K, determine (c) the fouling factor that caused the reduction in the overall heat transfer coefficient.

Question

Hot water (cph = 4188 J/kg·K) with mass flow rate
of 2.5 kg/s at 100°C enters a thin-walled concentric tube
counter-flow heat exchanger with a surface area of 23 m2
and an overall heat transfer coefficient of 1000 W/m2·K.
Cold water (cpc = 4178 J/kg·K) with mass flow rate of 5 kg/s
enters the heat exchanger at 20°C, determine (a) the heat
transfer rate for the heat exchanger and (b) the outlet temperatures
of the cold and hot fluids. After a period of operation,
the overall heat transfer coefficient is reduced to 500 W/m2·K,
determine (c) the fouling factor that caused the reduction in
the overall heat transfer coefficient.