Hot water at an average temperature of 80 C is flowing through a 15-m section of a cast iron pipe (k = 55 W/m.K) whose inner and outer diameters are 4 cm and 4.6 cm, respectively. The outer surface of the pipe, is exposed to the cold air at 5 C in the basement, with a heat transfer co- efficient of 25 W/m2.K.
The heat transfer co-efficient at the inner surface of the pipe is 150 W/m2.K.
Taking the walls of basement to be at 5 C also, determine the average velocity of the water in the pipe if the temperature of the water drops by 3 C as it passes through the basement.