Evaluation of Heterogeneous Nucleation Phenomena on a Cold Substrate of a Binary Vapor Mixture

通过缓慢冷却铜基片，进行了苯和环己烷混合蒸气到晶体或液滴的非均相相变实验。为了评价从进料器到冷阱的蒸气压变化，测量了稀薄气体流经内径为3 mm、长度为5-100 mm的五种圆柱体的热导率。根据平衡热力学和经典成核理论，研究了混合蒸汽的非均质成核特性。在实验结果和经典成核理论的基础上，采用动力学模型模拟了低衬底温度下封闭腔室中的非均相汽-晶或液滴相变。结果表明：1.根据二元混合物在气-固体系和气-液体系中的低共熔和共沸性质，在各组分的高组成区形成纯固体，在中间组成区形成液体混合物.在相同的平均压力P =（P_1 + P_2）12时，上、下游容器压力比为P_1/P_2=2- 10时的流导明显小于<av>压力比接近1时的流导.液相混合物的形成是在热力学平衡条件下进行的。

The experiments for the heterogeneous phase transition from mixed benzene and cyclohexane vapor to crystal or liquid droplet were conducted by slowly cooling a copper substrate. In order to evaluate the change in vapor pressure from a feeder to a cold trap, the conductances for rarefied gas flow through five kinds of cylinders with a inner diameter of 3 mm and 5-100 mm length ware measured. The heterogeneous nucleation characteristics of the mixed vapor ware examined on the basis of the equilibrium thermodynamics and classical nucleation theory. On the basis of both experimental results and the classical nucleation theory a dynamic model was used to simulate the heterogeneous vapor-to-crystal or liquid droplet phase transition in a closed chamber at low substrate temperature. The following results ware obtained.1 .According to eutectic and azeotropic nature of the binary mixture in the vapor-solid system and in the vapor-liquid system, respectively, pure solids formed in the region of higher composition of each component and liquid mixture formed in the region of intermeadiate composition.2. The conductance in the case of the ratio of pressures in gas containers in the upstream side and downstream side P_1/P_2=2-1O was significantly less at the same average pressure P_<av> = (P_1 + P_2) 12 than that in the case of the pressure ratio of near unity.3. The formation of liquid mixture occurred under the thermodynamical equilibrium condition.