A 5-m-long section of hot and water pipe run parallel to each other in a thick concrete layer, as shown in figure. the diameters of both pipes are 5cm, and the distance between the centerline of the pipe is 30cm. the surface temperature of the hot and cold pipe are 70c and 15c, respectively. taking the thermal conduction of the the concrete to be k=0.75, determine the raet of heat transfer between the pipe.