Steel balls 12 mm in diameter are annealed by heating to 1100 K and then slowly cooling to 380 K in an air environment for which [infinity] 325 K and 20 W/m2·K. Assuming the properties of the steel to be 40 W/m·K, 7800 kg/m3, and 600 J/kg·K, estimate the time required for the cooling process.

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]