Work/heat transfer of a heat exchanger Only flow work (boundary)for the CV-> licy =0 High rate of heat transfer from stream to stream (internal) Low rate of heat transfer between CV and surrounding Common assumptions for heat exchangers SSSF:no changes with time -APE =0:small elevation change -negligible△KE terms Fluid B CV boundary Fluid B CV boundary Negligible heat transfer between external enclosure of heat exchanger shell and Fluid A Heat Fluid A surroundings (external surface area is small Heat compared to surface area that exchanges heat between the two fluids) (a)System:Entire heat (b)System:Fluid A (Ocy0) The pressure of each fluid does not change as it exchanger (Ocv =0) flows through the heat exchanger 上游充通大 April 5,2018 3 SHANGHAI JIAO TONG UNIVERSITYApril 5, 2018 3 Work/heat transfer of a heat exchanger Only flow work (boundary) for the CV High rate of heat transfer from stream to stream (internal) Low rate of heat transfer between CV and surrounding CV W  0 Common assumptions for heat exchangers – SSSF: no changes with time – ∆PE = 0: small elevation change – negligible ∆KE terms – Negligible heat transfer between external enclosure of heat exchanger shell and surroundings (external surface area is small compared to surface area that exchanges heat between the two fluids) – The pressure of each fluid does not change as it flows through the heat exchanger