Accounting for the effect of the heat exchanger length in the performance evaluation of compact fin and tube heat exchangers

Often a performance evaluation criterion (PEC) is used to compare different fin geometries. Based on several assumptions and imposed constraints, the PEC can predict the performance of a heat exchanger using the considered fin geometry. One of these assumptions is that the fin characteristics are independent of the heat exchanger length. Different fin geometries however result in heat exchanger designs with different lengths. In this work the effect of the length is investigated for compact (Dh < 6 mm) fin and tube heat exchangers. The heat exchanger length is fully defined by the number of tube rows and the longitudinal tube pitch. In order to be able to construct the heat exchanger, the value of these parameters must be compatible with the heat exchanger length as described by the PEC. The longitudinal tube pitch of a heat exchanger as determined from a PEC analysis is therefore dependent on the fin geometry used for that heat exchanger. It is shown that for heat exchangers with a small number of tube rows, it is necessary to properly account for the influence of this parameter. In this paper, a method is developed to compare heat exchangers with an arbitrary number of tube rows while accounting for longitudinal tube pitch effects.