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QUESTION 1 A counter flow double pipe heat exchanger using super-heated steam is used to heat water at the rate of 8000 kg/hr. The steam enters the heat exchanger at 180C and leaves at 130 C. The inlet and exit temperatures of water are 30 C and 80C respectively. If the overall heat transfer coefficient from steam to water is 814 W/m2 K, calculate: 2 (10) 1.1 Heat transfer area. (Hint- use arithmetic mean temperature difference) 1.2 What would be the increase in area if the fluid flow was parallel? (10) QUESTION 2 Consider cold water flowing through in a Dibone tube counter-flow heat exchanger to cool hot oil. The inner tube made with carbon has a diameter of 2 cm with negligible wall thickness. The inner diameter of the graphite shell is 3 cm. The oil flows through the graphite shell at a rate of 0.8 kg/s while water flows through the tube at a rate of 0.5 kg/s. The oil through the annulus has a convection heat transfer coefficient of hs = 75.2 W/m2K Water properties are given below: p = 990.1 kg/m3 k = 0.637 W/m.K Pr = 3.91 V = 0.602 x 10-6 m/s 2.1 Determine if the water flow is turbulent or laminar (4) 2.2 Determine the convection heat transfer coefficient for water (3) 2.3 Determine the overall heat transfer coefficient of this heat exchanger. (3) ii [TURN OVER] Hot oil 0.8 kg/s) Cold water 0 0.5 kg/s 12 cm 3 cm