Plasma hydrophilic surface treatment for dehumidifying heat exchangers

This paper describes a method using plasma gas to form a hydrophilic surface on fin stock for dehumidifying finned-tube heat exchangers. The heat exchangers (with and without the plasma treatment) were subjected to 1000 wet/dry cycles and the contact angle was measured as a function of cycling time. The heat transfer and pressure drop characteristics of these heat exchangers were then measured in a wind tunnel after each 250 wet/dry cycles. Data was taken for dry and wet surface (de-humidification) heat transfer on both untreated and treated surface heat exchangers. After 1000 wet/dry cycles, the wet surface pressure drop on the plasma treated surface was 30% greater than the dry surface value, as opposed to a 100% pressure drop increase for the untreated surface heat exchanger. This data shows that the plasma treatment provides long-term pressure drop reduction. For fixed air frontal velocity, the plasma treated and untreated heat exchangers give practically the same air-side heat transfer coefficient. However, the plasma treated heat exchanger yields 25% lower air pressure drop than the untreated heat exchangers for the fully wet condition. Hence, at fixed frontal velocity, the plasma treated heat exchanger will require less fan power for the same cooling duty and will result in reduced fan noise. (C) 2002 Elsevier Science Inc. All rights reserved.