Comparison of Boiling characteristics between Conventional and Environmentally Accepted New Freons

实验结果总结如下：1。混合物的核池沸腾——对不同成分的混合物Rll-Rll3和乙醇水在较宽的压力和热流密度下进行了试验。(i)现有的传热变质预测方法，通常在混合物沸腾中遇到，不能再现所观察到的变质率随压力的变化。（ii）传热系数从预测值向较低挥发性成分浓度偏移最小的观测组成。（iii）如果根据与混合物具有相同性质的假想纯液体的传热系数来评估传热恶化，则传热恶化可能与传质阻力有关。现有的纯液体关系式对这一目的毫无用处。混合物的流动沸腾——对混合物Rll-Rll3在垂直管内进行了不同成分、质量、速度和热流密度的流动沸腾试验。(i)在低质量情况下，还观察到池沸过程中的传热恶化。（ii）对应于从有核沸腾到两相强制对流的过渡，混合物的换热系数也随着质量的增加而逐渐升高，但过渡质量有所降低。（iii）在高质量的情况下，没有观察到混合物的传热恶化。（iv）现有的沸点数相关性不能涵盖压力范围很广的数据。提出了新的相关性，以解释在低质量下观察到的传热恶化。Altei原生氟利昂的池沸——采用新型氟利昂R123 （Rll的替代品），在压力P= 0的范围内，从上面向板进行了饱和沸腾实验。l ~ 3.2 MPa，热流密度q=3000 ~ 600000 W/m2。(i)换热系数水平以及压力和热流密度的影响与Rll相似。（ii）实验换热系数h[W/m2K]与h = 1.58 f(P/Pc)* qO关系良好。8,问:热通量(W / m2), P / Pc:减压(-)和F (P / Pc) = 0.23 (P / Pc) / (1 - 0.99 * 0.9 (P / Pc))。（三）Zuber相关性适用于预测临界热通量。少

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