Analysis of heat-transfer performance of cross-flow fin-tube heat exchangers under dry and wet conditions

Abstract

A three-dimensional analysis procedure for the detailed phenomenon in a fin-tube heat exchanger has been developed and applied to predict the heat/mass transfer characteristics of the wave-fin heat exchangers. The continuity, Navier-Stokes and energy equations together with the species equation for the air-vapor mixture are solved in a coupled manner, so that the inter-dependence between the temperature and the humidity can be properly taken into account, by using the SIMPLE-type finite volume method. Having validated the procedure, calculations have been carried out for various frontal-velocity and inlet-humidity conditions. It has been shown that the flow characteristics, such as the temperature and humidity fields, along with the local heat flux and the condensation rate, can be successfully captured. The numerical results reveal that the existing correlations considerably underestimate the fin efficiency especially for multi-row heat exchangers. For dehumidifying cases, the sensible heat-transfer rate seems insensitive to the inlet-humidity change. The rate changes mostly in the narrow band of partially wet regime between 25% and 40% of inlet relative humidity. The range of the frontal velocity that gives the best performance for various numbers of rows is also estimated. The analogy between the heat and mass transfer on the fin surface is also examined. (C) 2011 Elsevier Ltd. All rights reserved.