Theoretical model to estimate fluid distribution in compact heat exchangers

Abstract

One of the limitations to design a compact heat exchanger is the phenomenon of fluid maldistribution. Most research considers a uniform fluid distribution in the channels, which can be considered a wrong approximation, since the non-uniform fluid distribution can seriously affect the performance. There are few experimental and numerical studies related to fluid distribution in a compact heat exchanger, however, currently, there is no mathematical model capable of predicting the fluid distribution within the channels. The present work developed the first theoretical model capable to estimate the flow distribution inside compact heat exchanger channels. The model is based on the concept of the shape factor, relating the radiation ratio between surfaces with the mass flow rate. The model considers geometric parameters to estimate the fluid distribution, such as channel position, channel cross-sectional area, fluid inlet surface area, and inlet header depth. In order to verify the model's accuracy, comparisons with experimental and numerical data available in the literature were performed, besides, a test facility was produced and used to test two header configurations. The average error of the model was approximately 9%, having a better performance than the hypothesis of uniform distribution, which presented an average error of 13%. However, in cases where fluid maldistribution was pronounced, the model exhibited significantly better results, reducing the error from 29%, uniform distribution hypothesis, to 11%. This demonstrates that the model can be applied to estimate fluid distribution inside de core and enhance the design of heat exchangers.