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# solution#5.doc - 5-85 Ethylene glycol is cooled by water in...

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5-85 Ethylene glycol is cooled by water in a heat exchanger. The rate of heat transfer in the heat exchanger and the mass flow rate of water are to be determined. Assumptions 1 Steady operating conditions exist. 2 The heat exchanger is well-insulated so that heat loss to the surroundings is negligible and thus heat transfer from the hot fluid is equal to the heat transfer to the cold fluid. 3 Changes in the kinetic and potential energies of fluid streams are negligible. 4 Fluid properties are constant. Properties The specific heats of water and ethylene glycol are given to be 4.18 and 2.56 kJ/kg. ° C, respectively. Analysis ( a ) We take the ethylene glycol tubes as the system, which is a control volume. The energy balance for this steady-flow system can be expressed in the rate form as Then the rate of heat transfer becomes ( b ) The rate of heat transfer from glycol must be equal to the rate of heat transfer to the water. Then, 5-96 Two streams of water are mixed in an insulated chamber. The temperature of the exit stream is to be determined. Assumptions 1 This is a steady-flow process since there is no change with time. 2 Kinetic and potential energy changes are negligible. 3 There are no work interactions. 4 The device is adiabatic and thus heat transfer is negligible. Properties From the steam tables (Table A-4), h 1 2245 h f @ 90 ° C = 377.04 kJ/kg h 2 2245 h f @ 50 ° C = 209.34 kJ/kg Analysis We take the mixing chamber as the system, which is a control volume since

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## This note was uploaded on 01/22/2012 for the course MSE 150 taught by Professor Kkk during the Spring '11 term at Albright College.

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solution#5.doc - 5-85 Ethylene glycol is cooled by water in...

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