Water used in a power plant passes through a heat exchanger at a mass flow rate of 0.125 kg/s, and is cooled from 94°C to 26°C by passing it through a smooth tube of inner diameter of 25 mm and a length of 25 m. The coolant is air and is maintained at 20°C and has a velocity of 20 m/s in cross flow over the tube. Determine the thermal entry length and the rate of heat transfer to the air.