Augmentation of Thin Falling-Film Evaporation on Horizontal Tubes Using an Applied Electric Field

Abstract

Heat transfer enhancement of falling-film evaporation on commercially available horizontal tubes using an applied electric field was studied experimentally. The tube surfaces tested included: smooth, 19 fins per inch (19 fpi) low-fin type, and Turbo BIII which is a state-of-the-art commercially available boiling tube. The nominal outside diameters of all the tubes were 19 mm. Experiments were performed with R-134a at a saturation pressure of 550 kPa. Effects of heat flux, film flow rate, applied electric field potential, and heat transfer surface on the heat transfer coefficient were investigated. In addition, the effect of Poloyl-ester oil on the heat transfer coefficients was also investigated. Experiments were conducted for oil concentrations ranging from 0.5 percent to 5 percent on a mass basis. Small concentrations of a poloyl-ester lubricant were found to improve the heat transfer performance, while large concentrations reduced the heat transfer coefficient. [S0022-1481(00)00702-7]