Thermal and hydrodynamic analysis of a cross-flow compact heat exchanger

Abstract

Compact heat exchangers are used in the industry to perform the heat transfer between two fluids at different temperatures. Characterized by high heat transfer area and rate per unit volume, they are mainly used for applications where space is restricted. In the current study, a complete analysis of heat transfer and pressure drop of a diffusion bonded stainless steel heat exchanger is performed. A model to predict the pressure drop in the heat exchanger is presented, highlighting the contribution of the major components of the equipment: core and headers. Three correlations, which main input parameter is the dimensionless hydrodynamic length, were used to predict the friction factor inside the channel. A cross-flow heat exchanger with mini square cross section channels, of 3 mm of edge, was manufactured. In order to validate the model and to study the thermal and hydrodynamic behavior of the equipment, an experimental test apparatus was developed. The heat exchanger was tested with water at different levels of mass flows. Experimental thermal results were compared with the theoretical model with small disagreement. To improve this comparison, an adaptation of a Nusselt number correlation, for square channels, was proposed, showing now a good convergence to the data. The hydrodynamic results showed that headers were responsible for at least 50% of the heat exchanger pressure drop. Besides this study, numerical simulations were performed. Finally, numerical, experimental and theoretical results were compared, showing similar trends, validating, this way, the theoretical model and the numerical procedures.