Water thickness effect on the fin efficiency and heat transfer for partially wet-surface heat exchanger

Abstract

Heat and mass transfer, in this paper, is considered in one-row heat exchanger, that fins are hotter than air flow and water is added to fins. Related governing equations are derived by analyzing a two-dimension model in a unique cell of a heat exchange. These equations are numerically solved by finite difference method. Heat transfer and efficiency under partially wet surface are calculated by changes in thickness of water layer on the fins and wet percentage region of fin with constant airflow characteristics. In this study, Lewis Number as unity and water vapor saturation as parabolic are assumed. Obtained results show that increasing in thickness of fin leads to increasing thermal resistance; therefore, efficiency of fin decreases. But thickness of water layer dose not play a significant role in fin efficiency when water layer covering the surface of fins is thin or it covers a small region of fins because thermal resistance of water is not comparable with thermal conductivity of fin material. But where thickness of water layer is comparable with fin pitch or more surface of fins is wetted, fin efficiency and heat transfer change obviously because of increasing thermal resistance and changing in air flow velocity that cause more decreasing in efficiency of fins.