Comparison of Boiling characteristics between Conventional and Environmentally Accepted New Freons

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Results are summarized about three major experiments as follows.1. Nucleate Pool Boiling of Mixtures --- Mixtures Rll-Rll3 and Ethanol Water of different compositions were tested under the wide ranges of pressure and heat flux. (i) The existing predictive methods of heat transfer deterioration, encountered usually in mixture boiling, cannot reproduce the observed change with pressure of the deterioration rate. (ii) The observed composition where the heat transfer coefficient takes the minimum shifts from the predicted value to lower concentration of more volatile component. (iii) Heat transfer deterioration might be related to the mass transfer resistance, if the deterioration was evaluated based on the heat transfer coefficient of the imaginary pure liquid with the same properties as the mixture. Existing correlations proposed so far for pure liquids are of no use for this purpose.2. Flow Boiling of Mixture --- Mixture Rll-Rll3 in a vertical tube was tested varying composition, mass v … More elocity and heat flux. (i) At low quality, the heat transfer deterioration encountered in pool boiling is also observed. (ii) Corresponding to the transition from the nucleate boiling -io the two-phase forced convection, the heat transfer coefficient for mixtures also rises gradually with increasing quality, but the transition quality is somewhat lower. (iii) At high quality, The heat transfer deterioration is not observed for mixtures. (iv) The existing correlations with the boiling number cannot cover the data over the wide range of pressure. The new correlation was proposed accounting for the heat transfer deterioration observed at low quality.3. Pool Boiling of Altei, native Freons --- By using the new freon R123, an alternative to Rll, the saturated boiling from the upward-facing plate was experimented over the ranges of pressure P=O. l to 3.2 MPa and heat flux q=3000 to 600000 W/m2. (i) Both the level of heat transfer coefficient and effects of pressure and heat flux are similar to those for Rll. (ii) Experimented heat transfer coefficient h[W/m2K]is well correlated by h = 1.58 f(P/Pc)* qO. 8, where q : heat flux[W/m2], P/Pc : reduced pressure[-]and F(P/Pc)=(P/PC)0.23/(1-0.99*(P/Pc)0.9). (iii) Zuber's correlation is applicable to predict the critical heat flux. Less