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Journal of Enhanced Heat Transfer
Alternative Approach for Determining Log Mean Temperature Difference Correction Factor and Number of Shells of Shell and Tube Heat Exchangers
Department of Mechanical Engineering, Bradley University, Peoria, Illinois, USA
The challenge of enhancing or optimizing the rate of heat transfer from heat exchangers is compounded by the lack of a simple and generally applicable approach for its analysis. Because the expressions for the log mean temperature difference (LMTD) correction factor, F, or those for heat exchanger effectiveness, e, are difficult to evaluate, the traditional analysis methods rely on heat exchanger specific charts. In addition to being applicable only to a particular heat exchanger, these charts are highly nonlinear and strongly dependent on the traditional parameters used for their evaluation. Expressed in terms of the nondimensional parameters P and R, the LMTD correction factor F charts are particularly difficult to read in the steep regions. These shortcomings also make the assessment of different heat transfer enhancement strategies tedious. In this study, an alternative approach for determining F in terms of two new nondimensional parameters, r and f, is presented. This new approach results in a single general algebraic equation for determining the LMTD correction factor of multipass shell and tube heat exchangers with any number of shell passes and an even number of tube passes per shell. This single expression can be used to devise and compare different enhancement strategies for shell and tube heat exchanger networks, including their arrangement, to optimize their rate of heat transfer. It is shown that the approach presented results in a novel expression for the determination of the number of shells needed to meet a predefined overall correction factor for multishell and tube heat exchangers.
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