VISUALIZATION OF NUCLEATE FLOW BOILING FOR AN R22/R114 MIXTURE AND ITS COMPONENTS

Abstract

Visualization of bubble nucleation during forced-convective flow inside a horizontal, electrically heated quartz tube was done in order to establish a comparison of this phenomenon between refrigerant mixtures and their pure components. The specific phenomena investigated were the suppression of nucleation due to increased mass flow quality while holding all other conditions fixed, and the comparison of the nucleate activity of the binary mixture to the nucleate activity of the pure components. The fluids investigated were a 37.7 mol° R22/62.3 mol° R114 binary mixture and the individual components R22 and R114. These fluids were pumped through an abraded, electrically heated quartz tube. A 16-mm high-speed camera was used, at 7000 frames/s, to film the boiling process. Detailed measurements of bubble frequency and bubble size were possible at low pressures, allowing direct calculation of the latent heat load required to nucleate a single bubble. Further work is required to develop a method that ensures statistically sound bubble frequency measurements. However, the standard deviations of the bubble diameter measurements were acceptable. The films were used to visually demonstrate the suppression of nucleation with increase in quality for R114, R22, and an R22/R114 mixture. The films suggest that, for a given quality, RI14 exhibits much more nucleation than either R22 or the mixture, while the amount of nucleation demonstrated by R22 and the mixture was comparable even though the mixture was mostly R114 by mole. Arguments using the latent heat of vaporization, the vapor density, and the liquid thermal conductivity have been made to explain the visual trends.