A horizontal pipe with flowing water is placed in a still air at temperature Ta=20C and used as an air heater. The pipe has the inner diameter d=50 mm and outer diameter do=60 mm while its length is L=30 m. The water temperature at the pipe inlet is Tw1=82.5 C and the outlet Tw2=77.5 C . Find the heat loss per unit time (heat rate) from the pipe to the surrounding air and the mean velocity of water in the pipe. Assume that the temperature on the outer surface of the pipe is close to the mean temperature of water in the pipe. This assumption is reasonable due to high thermal conductivity of the pipe material and great convective heat transfer coefficient on the water side of the pipe.