Optimal designs for flow uniformity at inlet of microchannel flat tube heat exchanger

Abstract

Microchannel flat tube heat exchangers and circular tubes commonly used in thermal engineering applications vary in size and shape. Uniform flow distribution is an essential factor affecting the performance of heat exchangers. This paper proposes three types of inlet distributors to achieve connection and reduce the non-uniformity of the working fluid flow: Column-type, Diffuser-type, and Drainage-type. The flow uniformity, pressure drop, and heat transfer efficiency of R410A refrigerant two-phase flow in a microchannel flat tube heat exchanger with various mass fluxes are investigated by numerical simulation. Verification is done by experiment and empirical correlation. The concept of heat transfer offset rate is proposed to characterize the impact of flow uniformity on heat transfer. The eddy current at the distributors is a significant factor in the uneven distribution of the flow field. Different distributors will affect the distribution of gas and liquid phases. The standard deviation of the mass flow rate in Column-type is less than 9.10%, and uniformity is best when the mass flux is low. The heat transfer coefficient is 5800 W/m2K, and the heat transfer offset rate is less than 5.77%. When the mass flux exceeds 300 kg/(m2s), the flow distribution performance of the diversion flow is the best, and the flow standard deviation can be reduced by up to 36.56% at high flow.