Answer Happy

Problem 07.084- Cooling of Hot Water Tank Consider a 50-cm-diameter and 95-cm-long hot water tank. The tank is placed on the roof of a house. The water inside the tank is heated to 80°C by a flat-plate solar collector during the day. The tank is then exposed to windy air at 25°C with an average velocity of 40 km/h during the night. Estimate the temperature of the tank after a 45-min period. Assume the tank surface to be at the same temperature as the water inside, and the heat transfer coefficient on the top and bottom surfaces to be the same as that on the side surface. Evaluate the air properties at 50°C. The properties of water at 80°C are p=971.8 kg/m³ and cp=4197 J/kg-"C. The properties of air at 1 atm and at the film temperature of 50°C (based on the problem statement) are k = 0.02735 W/m "C. v-1.798 x 10-5 m2/s, and Pr=0.7228. The temperature of the tank after a 45-min period is *C.