Heat Transfer HEAT EXCHANGERSSingle-phase heat exchangers are usually of the tube-and-shell type; that is, the exchangerconsists of a set of tubes in a container called a shell (Figure 8). At the ends of the heatexchanger, the tube-side fluid is separated from the shell-side fluid by a tube sheet. The designof two-phase exchangers is essentially the same as that of single-phase exchangers.Figure 8 Typical Tube and Shell Heat ExchangerParallelandCounter-FlowDesignsAlthough ordinary heat exchangers may be extremely different in design and construction andmay be of the single- or two-phase type, their modes of operation and effectiveness are largelydetermined by the direction of the fluid flow within the exchanger.The most common arrangements for flow paths within a heat exchanger are counter-flow andparallel flow. A counter-flow heat exchanger is one in which the direction of the flow of oneof the working fluids is opposite to the direction to the flow of the other fluid. In a parallel flowexchanger, both fluids in the heat exchanger flow in the same direction.Figure 9 represents the directions of fluid flow in the parallel and counter-flow exchangers. Undercomparable conditions, more heat is transferred in a counter-flow arrangement than in a parallelflow heat exchanger.Rev. 0 Page 31 HT-02
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