A counter flow, concentric tubes heat exchanger is designed to heat whether from 20 0C to 80 0C using hot oil flowing through the annulus. The oil temperature gets reduced from 1600C. The nominal diameter of the inner tube is 20 mm and the corresponding overall heat transfer coefficient is 500 W/m2-K. The heat transfer rate from the oil is 3000 watts. Determine the length of the exchange. Because of fouling after some days the outlet temperature of water reduced to 65 0C for the same flow rates and same inlet conditions. Determine the outlet temperature of oil, the fouling factor and the new heat transfer rate.
Sketch the heat exchanger arrangement and the temperature profiles.