Measurement and Modeling of Void Fraction in High-Pressure Condensing Flows Through Microchannels

Void fraction measurements are obtained using high-speed video for the condensation of R404A in tubes of diameter 0.508, 1.00, and 3.00mm. Experiments were conducted on refrigerant R404A throughout the entire condensation quality range (0.05-0.95) at varying mass fluxes (200-800kg m(-2) s(-1)) and saturation temperatures from 30 to 60 degrees C (which correspond to the reduced pressure range 0.38-0.77). These high pressures are representative of actual operation of air-conditioning and refrigeration equipment. The influence of saturation temperature on void fraction is most pronounced in the quality range 0.25-0.75. In addition, it was found that the influence of mass flux on void fraction was negligible for all saturation temperatures and tube diameters investigated. Three void fraction models from the literature are compared with the data. Of these, the Baroczy correlation predicted the data the best, with an overall absolute average deviation of 11.2%. A new drift flux void fraction model is developed to predict void fraction for condensing flows in microchannels and compared with the R404A data and R134a void fraction data from Winkler etal. Overall, the model is able to predict 92.3% of the R404A data and 81.6% of all refrigerant data within 25%.