Scope and Method of Study. Frosting tests were conducted on seven different microchannel heat exchanger geometries to investigate capacity degradation and rate of frost growth. Every fin sample was tested with three different fin temperature conditions with air entering the fin sample at 1.7°C (35°F) dry bulb temperature and wet bulb temperature of 0.6°C (33°F), which yield entering relative humidity of about 82% and absolute humidity of 0.0035 kg-water/kg-air. The air face velocity on fin sample at the beginning of the test was set to 1.5 m/s (295 fpm) for fin sample 1, 2, 3, 6, and 7. The air face velocity was varied at 0.8, 1.2, and 1.6 m/s (157, 236, and 315 fpm) on fin sample 4. Fin sample 5 face velocity was set to 1 m/s (197 fpm). Additionally, the effect of humidity content in the air was investigated on sample 4 where the humidity ratio was varied from 72% to 92%.

Findings and Conclusions. The experimental results suggested that fin temperature and air humidity had a predominant effect on frost growth rate. Meanwhile, air velocity was peculiar and further investigations are recommended in the future. The frost tests on different fin geometries (fin height, fin depth, and fin density) recommended that folded flat fins seemed to have higher frosting time due to a lower heat transfer capacity when compared to folded louvered fins at the same fin temperature. Meanwhile, the effect of frosting time for different geometries were significant when the fin temperature is warmer in the experimental case is at -5°C (23°F). On the other hand, when the fin temperature decreased below -10°C (14°F) the effect of fin geometries on the frosting time became less significant. The impact of the frosting time and heat transfer rate is due to different fin geometries which are presented in this thesis.