Thermal analysis of a counterflow heat exchanger with a heat source

SYNOPSIS A modified analysis is presented of a counterflow plate heat exchanger that takes into account a heat source, which is assumed to be volumetrically uniform in the hot fluid. New expressions for the number of transfer units (NTU) and effectiveness of the heat exchanger are derived. These expressions are verified against the conventional effectiveness-NTU relationships in the limit of zero heat source rate. Such heat exchanger with heat source in the hot fluid is of interest in applications to ammonia-water absorption heat exchanger where a heat of absorption source term arises in the solution side. The model studies two cases based on the minimum and maximum heat capacities of the hot fluid. The results show that the number of heat transfer units and the effectiveness of the heat exchanger are not the same for both cases. The analysis is applied to an absorber heat exchanger. Effectiveness-NTU relationships are also given for a parallel flow heat exchanger with a heat source in the hot fluid.