An open wall consist in succession layer of fire bricks (Kf=1.21j/m²°C) a layer of lagging bricks(Kl=0.08j/m²°C) and a layer of bricks (Kb=0.6m²°C)each layer is 10cm thick, the temperature in the inside of the wall is 872°C ,on the outside 32°C. calculate the following (a)heat lost by conduction every 12 hours if the surface area of the wall is 20 m² (b) temperature in the middle of the layer of lagging bricks (c)overall heat transfer coefficient

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]