Heat exchanger analysis the effectiveness-NTU method

The effectiveness—NTU method is a procedure for evaluating the performance of heat exchangers, which has the advantage that it does not require the evaluation of the mean temperature differences. NTU stands for the Number of Transfer Units, and is analogous with the use of transfer units in mass transfer see Chapter 11. 

The principal use of this method is in the rating of an existing exchanger. It can be used to determine the performance of the exchanger when the heat transfer area and construction details are known. The method has an advantage over the use of the design procedure outlined above, as an unknown stream outlet temperature can be determined directly, without the need for iterative calculations. It makes use of plots of the exchanger effectiveness versus NTU. The effectiveness is the ratio of the actual rate of heat transfer, to the maximum possible rate. 

The effectiveness-NTU method will not be covered in this book, as it is more useful for rating than design. The method is covered in books by Incropera and Dewitt (1996), Ozisik (1985) and Hewitt et al. (1994). The method is also covered in the Engineering Sciences Data Unit, ESDU 86018 (1986). This reference gives large clear plots of effectiveness versus NTU and is recommend for accurate work. 

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