It is desired to chill 3m of water per hour by means of horizontal coils in which ammonia is evaporated. The steel coils are 2.13cm outside diameter and 1.71cm inside diameter and the water is pumped across the outside of these at a velocity of 0.8 ms'. Estimate the length of pipe coil needed, if the mean temperature difference between the refrigerant and the water is 8C, the mean temperature of the water is 4C and the temperature of the water is decreased by 15C in the chiller. (53.1m)