Water (specific heat 4.2 kj/kg C) at the rate of 120 kg/min is heated from 20 to 70 C by an oil having a specific heat of 2.0 Kj/KgC in a counter-flow double-pipe heat exchanger. Oil enters at the temperature of 120 C and leaves at 40 C. The overall heat transfer coefficient is 250 W/m2C.
Calculate the area required for the exchanger.
Using the same inlet temperatures of the above problem, calculate the temperatures when the water rate is reduced by 30%. What is the total heat transfer under this new condition ?