Across-flow air-to-water heat exchanger (both fluids unmixed) with an effectiveness of 0.65 is used to heat water (cp 4180 j/kg. k) with hot air (c 1010 j/kg. k). water enters the heat exchanger at 20°c at a rate of 4 kg/s, while air enters at 100 c at a rate of 9 kg/s. if the overall heat transfer coefficient based on the water side is 260 w/m2.k, determine the heat transfer surface area of the heat exchanger.

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]