A 3-m-diameter spherical tank containing some radioactive material is buried in the ground (k = 1.4 W/m·K). The distance between the top surface of the tank and the ground surface is 4 m. If the surface temperatures of the tank and the ground are 180°C and 15°C, respectively, determine the rate of heat transfer from the tank.

Athin walled concentric tube exchanger is used to cool engine oil from 160°c to 60°c with water that is available at 25°c acting as a coolant. the oil and water flow rates are each at 2 kg/s, and the diameter of the inner tube is 0.5 m and the corresponding value of the overall heat transfer coefficient is 250 w/m2. oc. how long must the heat exchanger be to accomplish the desired cooling? cpwater=4.187 kj/kg-candcpengine el=2.035 kj/kg·°c, oil . 120]