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Unformatted text preview: Chapter 11 Supplemental Material 11S.1 Log Mean Temperature Difference Method for Multipass and CrossFlow Heat Exchangers Although flow conditions are more complicated in multipass and crossflow heat exchangers, Equations 11.6, 11.7, 11.14, and 11.15 may still be used if the follow ing modification is made to the log mean temperature difference [1]: (11S.1) That is, the appropriate form of D T lm is obtained by applying a correction factor to the value of D T lm that would be computed under the assumption of counterflow con ditions. Hence from Equation 11.17, D T 1 5 T h , i 2 T c , o and D T 2 5 T h , o 2 T c , i . Algebraic expressions for the correction factor F have been developed for vari ous shellandtube and crossflow heat exchanger configurations [13], and the results may be represented graphically. Selected results are shown in Figures 11S.1 through 11S.4 for common heat exchanger configurations. The notation ( T , t ) is used to specify the fluid temperatures, with the variable t always assigned to the tubeside D T lm 5 F D T lm,CF 0.2 0.6 0.4 1.5 1.0 0.8 3.0 2.0 6.0 4.0 R = T i T o ______ t o t i 1.0 0.9 0.8 0.7 0.6 0.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1.0 0.9 F P = t o t i _____ T i t i T i T o t i t o F IGURE 11S.1 Correction factor for a shellandtube heat exchanger with one shell and any multiple of two tube passes (two, four, etc. tube passes). c11_supl.qxd 1/19/06 4:57 PM Page W37 W38 11S.1 j Log Mean Temperature Difference Method 0.2 1.0 0.8 0.6 0.4 3.0 2.0 1.5 6.0 4.0 1.0 0.9 0.8 0.7 0.6 0.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 R = T i T o ______ t o t i F P = t o t i _____ T i t i T i T o t i t o F IGURE...
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 Spring '11
 Anthony

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