Condensate Drainage and Retention in Louver Fin Automotive Evaporators 2000-01-0575
Condensate that forms on the air side surface of an evaporator can have a significant impact on the air side performance of brazed aluminum, louver fin automotive evaporators. Condensate can “bridge” the space between two adjacent fins or louvers and alter the flow of air through the evaporator, causing a change in the heat transfer and friction characteristics. This study attempts to determine how condensate drains from an evaporator in the hopes of improving the air side fin geometry and obtain an evaporator that retains a minimum amount of condensate.
Using a table-top wind tunnel apparatus, qualitative observations of condensate draining from a single column of louver fins brazed to a refrigerant tube were made. The amount of condensate retained in an evaporator core was determined using the experimentally-verified dip test method. From this work, it has been determined that the louver pitch is the most important parameter in determining an evaporator’s ability to drain condensate. An evaporator with Lp = 1.1 mm retains 26% more condensate than an evaporator with Lp = 1.3 mm. This increase is due to an increase in condensate bridging of the louvers. Louver bridging occurs largely due to the existence of the louver cut end, where condensate may be pulled to and retained by surface tension. Almost no bridging of the fins occurs when Pf = 2.4 mm; but when Pf = 1.6 mm, significant fin bridging occurs and the amount of condensate retained increases by 32%. This increase occurs not only due to the decrease in the space between the fins but also because of the triangular shape of the fins when Pf = 1.6 mm. When the air side surface of the evaporator is smooth, condensate drains from the evaporator via three paths whose effectiveness is largely determined by the louver pitch. If there are channels on the air side surface of the tubes, almost all of the condensate is pulled into these channels by surface tension and drains down through the channels, out of the evaporator. Condensate can build up at the intersection of a fin base and a channel, leading to an increase in fin bridging.