Dynamic modeling of flow boiling within plate heat exchangers for heat pump and refrigeration applications

Abstract

Brazed Plate Heat Exchangers (BPHEs) are increasingly used as evaporators for refrigeration and heat pump applications. Detailed understanding of the underlying heat transfer phenomena is required for their effective design and use. The number of correlations which are suitable for modeling the dynamics of flow boiling within BPHEs is rather low compared to other evaporator types. In this paper some correlations that involve integral values of steam quality are evaluated for different sets of experimental data from literature. Modifications to the correlations are presented, which allow to predict the quasi-local heat transfer coefficient in each refrigerant cell. The cells equal finite volumes that are composed to a dynamic model of a BPHE acting as evaporator. Heat transfer coefficient and heat flow rate from simulation results are compared to those calculated from existing experimental data based on the same boundary conditions. The fine-tuned evaporator model is finally used to demonstrate effects of sudden load changes for the evaporator performance.