MECH3400 Study Guide - Quiz Guide: Heat Exchanger, Inq Mobile
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4: assumptions: steady state operating conditions; heat exchanger is well insulated so no heat losses to surroundings; negligible kinetic and potential energy effects; constant fluid properties. (a)rate of heat transfer: For water, qh2o = 4. 18 kj/kg/k x 0. 5 kg/s x (60-25) c = 73. 15 kj/s (b) The rate of entropy generation within the heat exchanger is determined by applying the rate form of the entropy balance on the entire heat exchanger: from the heat transfer occurring within the heat exchanger itself. As entropy change for an incompressible substance is given by: The entropy generation for the heat exchanger is consequently: To determine entropy change for the geothermal brine, we must know the exit temperature of the brine: =(tbrine,out tbrine,in) = qbrine/ mbrinecbrine, and as the system is well insulated, qbrine + qh2o = 0. Tbrine,out = tbrine,in qh2o/mbrinecbrine = 140 c 73. 15 kj/s / 0. 75 kg/s / 4. 31 kj/kg/k.
