Effects of frost growth on louvered folded fins of microchannel heat exchangers on the time-dependent air side convective heat transfer coefficient

This paper investigated the frost formation on louvered folded fins in microchannel type heat exchangers and the effects of frost accumulation on the time dependent air side convective heat transfer coefficients during transient heat and mass transfer processes. Seven fin geometries, which were commonly used in outdoor microchannel type heat exchangers of air-source heat pump systems, were investigated for a wide range of temperatures and humidity promoting frost growth. The air-side heat transfer coefficient was depended on the rate of frost growth and it sometimes increased during early frost formation and then it decreased sharply. Frost thickness on the fin leading edge, air face velocity, and corresponding heat transfer coefficients and pressure drops were measured and semi-empirical correlations were developed. The frost thickness and air face velocity were key variables for estimating a local time-dependent air-side Reynolds number and for describing the transient behaviour of the local air-side heat transfer coefficient of the fins. The newly developed correlations identified the main parameters that describe frost growth and heat transfer on louvered folded fins under frosting operating conditions and they agree with the experimental data of the present work and from the literature.