Wet Air Side Performance of Louver Fin Automotive Evaporators

Over the course of the past decade, the automotive industry has made efforts to reduce the depth of the brazed aluminum, louver fin evaporators typically used in the air conditioning system for automobiles by increasing their compactness. Increasing fin and louver densities have led to the possibility of condensate affecting the air side performance of automotive evaporators. Condensate can “bridge” the space between two adjacent fins or louvers. Condensate bridging of the fins or louvers can alter the flow of air through the evaporator, causing a change in the heat transfer and friction characteristics. This study attempts to quantify these changes and determine which parameters will have an impact on them.

Wind tunnel tests measuring the air side sensible heat transfer coefficient and pressure drop were conducted to examine how the air side heat transfer and friction characteristics of automotive evaporators are changed by the presence of condensate. These tests were performed on evaporators with fully dry and fully wet air side surfaces. It was found that there exists a critical louver pitch at which bridging of the louvers by condensate becomes so severe that the wet h_o suffers a significant reduction from the dry value. The value of L_p,crit lies somewhere between 1.1 and 1.3 mm when θ = 30°. An evaporator with drainage channels on the air side tube surface has a 30% higher wet to dry pressure drop ratio than an evaporator with a smooth air side tube surface, indicating that the drainage channels cause an increase in condensate bridging of the fins. The hydrophilic coating utilized in this study increased h_o,wet by 25% over an uncoated evaporator.