CH-12-034 (RP-1589) -- Measurements of Frost Growth on Louvered Folded Fins of Microchannel Heat Exchangers, Part 1: Experimental Methodology PDF

This paper is based on findings resulting from ASHRAE Research Project RP-1589.

Microchannel heat exchangers with louvered folded finsare subjected to frequent frost and defrost cycles when used inoutdoor evaporator coils of air-source heat pump systems.Despite their potential for heat transfer enhancements, understandingthe root causes that penalize microchannel heatexchangers during frosting operating conditions is still anopen field of study.

This paper presents a new experimental methodology tostudy frost growth on louvered folded fins of microchannel heatexchangers. The paper demonstrates the feasibility of the frostmass and frost thickness measurements and, through a seriesof controlled laboratory experiments, provides new data forfrost growth on louvered fins. Fin surface temperature wasdirectly measured during actual frosting operating conditions,and relations with heat transfer rates, air-side pressure drops,and frosting cycle times are discussed. The experimentalresults suggested that the frost mass increased linearly withtime and that there was no measurable time delay before watervapor began to frost and accumulate on the fins. The air-sideflow blockage due to frost accumulation on the front leadingedge of the fins was strongly dependent on the fin surfacetemperature, and the data confirmed that the flow blockagewas the key factor for the heat transfer capacity degradationduring frosting operation.