Effect of Boiling Condition on Vapor Concentration during Boiling of Liquid Mixture

近年来，为了实现高效的液气两相循环和工液的多种用途，非共沸工液在循环中的应用正在发展。阐明混合气液相变过程的特性是十分重要的。本研究的目的是阐明成核沸腾过程中液体混合物的沸腾条件对所产生蒸汽组成的影响。用细加热丝对水-乙醇和乙醇-丙酮混合物的饱和池沸腾过程中的大块蒸汽层进行了蒸汽浓度测量。两种测量方法；采用露点测量和已知液气平衡关系的露点法和利用红外光对碳氢化合物蒸气吸收特性的激光吸收法。结果表明，核沸腾产生的蒸汽层与体液处于平衡状态，且与沸腾条件如表面过热度、液层高度等无关。其次，测量产生蒸汽温度的变化，以阐明气泡产生和离开过程中蒸汽温度和浓度的变化。在受热面产生的汽泡具有较大的过热度。在气泡离开的过程中，发生了选择性冷凝，温度也随之降低。结果，气泡中的蒸汽几乎在距离受热面3-5毫米的高度与体条件达到平衡。气泡温度的变化由气泡产生的时间决定。从而阐明了在发生稳定沸腾和冷凝的系统中，蒸汽层浓度与体态处于平衡状态。少

Recently, the utilization of the non-azeotropic working fluid in the cycle is developing for achieving high performance liquid-vapor two-phase cycle and for the various usage of the working fluid. It is important to clarify the characteristic of the vapor-liquid phase change process of the mixtures. The objective of the study is to clarify the effect of the boiling condition of liquid mixture in the nucleate boiling process on the composition of the generated vapor. The vapor concentration measurement was carried out in the bulk vapor layer in the saturated pool boiling process of water-ethanol and ethanol-acetone mixtures from the thin heated wires. Two kinds of measuring method ; the dew-point method by using the dew-point measurement and the known liquid-vapor equilibrium relation, and the laser light absorption method by using the property of infrared light absorption to the vapor of hydrocarbon were adopted. As the result, it was clarified that the vapor concentration in the bulk … More vapor layer which was generated by the nucleate boiling was in equilibrium with bulk liquid and was independent on the boiling conditions such as the degree of surface superheat and liquid layer height etc. Next, the change of the generated vapor temperature was measured in order to clarify the variations of the temperature and concentration change of vapor in the process of the bubble generation and departure. The vapor bubble, which was created on heating surface, had comparatively large degree of superheat. The selective condensation was occurred and the temperature also lowered in the process of the departure of the bubbles. As a result, the vapor in the bubbles attained to be in equilibrium with the bulk conditions almost at the height of 3-5 mm from the heating surface. Moreover, the temperature change of vapor bubble was determined by the elapsed time from the vapor bubble generation. Thus, it was clarified that the concentration of vapor layer existed in equilibrium with the bulk state in the system in which the steady boiling and condensation was occurred. Less