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Exhaust gases flowing through a tubular heat exchanger at the rate of 0.4kg/s are cooled from 450C to 150C by water initially at 15C. The specific heats of exhaust gases and water may be taken as 1.13 and 4.19kJ/kgC respectively, and the overall heat transfer coefficient from gases to water is 140W/m2C. Calculate the surface area required for the following cases, when the cooling water flow is 0.5kg/s : (i) Parallel flow; (ii) Counter-flow, [Ans. (i) 4.84m2; (ii) 4.15m2]