Question

Twenty [kw] of heat is to be removed from 375 [k] water flowing at 0.15 [kg/s] into the inner pipe of concentric tube heat exchanger. Cooling water enters the annulus at 290 [k] and leaves at 320 [k] with a flow in the opposite direction of the inner flow. The diameter of the thin- walled inner pipe is 2.5 [cm] a) b) c) Calculate the exit temperature of the hot fluid and the mass flow rate of the cold fluid Calculate the heat transfer coefficient of the inner pipe. Assume fully developed flow Using an overall heat transfer coefficient of 600 [W/(m2k)] calculate the required length of the heat exchanger d Calculate the heat transfer area required if this was carried out using a shell-and-tube heat exchanger with the same overall heat transfer coefficient and the hot water in the shell and the cooling water in the tubes. Assume the correction factor, f, can be approximated with the relationship f(P, Z)-1-3P4 In(1.2+ Z*) Use the following mean property values Cold Hot 1.013x10-3 4.195 1.005x103 4.178 KJ K [W/(m*K)] N*s/m2 Pr 0.613 7.69x10-4 5.2 0.668 3.65x10-4 2.29

Answer 1

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