Entropy Generation Minimization for the Design of Plate Heat Exchangers

Plate heat exchangers are widespread in several fields due to their capability to transfer noticeable thermal powers despite the reduced encumbrance. The main feature concerns the presence of parallel plates where the fluids circulate in alternate manner in counter-current configuration. These devices are highly flexible allowing for the addition or the removal of a certain number of plates in order to vary the exchange surface. The latter often is equipped with corrugation in order to improve the thermal power transfer, however pressure drops can increase significantly. In this paper, a second law analysis was carried out in order to identify an optimal configuration of the heat exchanger that minimizes the entropy generation. The latter is determined by calculating the irreversibilities due to the heat transfer and the pressure drops. Usually, the first can be reduced with the exchange surface growth, but simultaneously the entropy generation due to the pressure drops increases. Therefore, these irreversibilities produce opposed effects and consequently an optimal configuration, that minimizes the total entropy generation, can be found. By means of a parametric study, a quality dimensionless index defined in function of the generated entropies allows for the identification of the optimal features of these heat exchangers.