Condensate formation and drainage on typical fin materials

Abstract

This work addresses contact angles on aluminum and copper surfaces and viable cleaning methods to promote surface wetting. Although the work involved fin materials used in dehumidifying heat exchangers, it has broader application, such as copper-water heat pipes. Condensate visualization tests were conducted on four typical fin surface materials, including aluminum, copper, and two commercial coatings on aluminum. Additional samples were created by further treatment of the basic surfaces. The treatments included acetone cleaning, grinding, and oil contamination. Observations were made using an apparatus that allows viewing of the condensate formed on a vertical flat surface with a humid air stream moving over it. The observations were quantified by measuring the condensate retention and the receding contact angle. Surface grinding yielded small receding contact angle of the aluminum and copper stocks; but, acetone cleaning was not effective for the bare aluminum and copper fin stocks. The surfaces having small receding contact angle provided film sheeting. However, condensate formed as droplets on those having higher receding contact angles. The weight of condensate retained per unit area was found to be an approximate function of the receding contact angle. As the receding contact angle increases, the retained condensate increases, reaching a maximum at approximately 40°, and then begins to decrease.