【作者】 胡自成；

【导师】 王谦；

【作者基本信息】 江苏大学 ， 工程热物理， 2012， 博士

【摘要】 能源紧缺和节能减排的急迫性要求尽可能提高沸腾传热设备的传热效率,沸腾传热强化的基础研究因此具有重要的理论意义和应用价值。添加表面活性剂的沸腾传热强化技术具有添加量少、强化效果显著和操作简单的特点而受到国内外的普遍关注,并成为传热科学研究中的热点课题。本文选定离子型表面活性剂SDS和CTAB水溶液、非离子型表面活性剂TritonX-114和Triton X-100水溶液为实验工质,对表面活性剂溶液物性、沸腾过程中蒸汽携带表面活性剂特性、表面活性剂溶液池核沸腾传热强化特性、表面活性剂溶液池核沸腾传热的影响参数识别体系构建、沸腾工况下表面活性剂溶液表面张力及接触角的理论计算、表面活性剂溶液池核沸腾换热关联式的开发等方面开展了系统的实验研究和理论研究,取得了一些具有学术意义和实用价值的研究成果：(1)针对选定的表面活性剂及其水溶液,测定了与沸腾传热相关的溶液物性,得出表面活性剂种类、溶液浓度和溶液温度等参数对热稳定性、浊点、表面张力、动力粘度和接触角的影响规律；考虑到沸腾过程中的蒸汽携带表面活性剂效应对表面活性剂溶液沸腾传热的影响,开展了沸腾过程中蒸汽携带表面活性剂的实验研究,获得了蒸汽携带表面活性剂效应对表面活性剂溶液沸腾传热强化效果的作用规律,为进一步研究表面活性剂溶液池核沸腾传热强化特性奠定基础。(2)对影响表面活性剂溶液池核沸腾传热的参数进行科学分类,分类考察并获得了不可变参数、可变参数和外部参数及参数耦合对表面活性剂溶液池核沸腾传热强化效果的作用机制,在此基础上构建了表面活性剂水溶液池核沸腾传热的影响参数识别体系。就影响参数的主次关系而言,溶液浓度、热流密度、动态表面张力和动力粘度是影响表面活性剂水溶液池核沸腾传热的关键影响参数；分子量、接触角、聚氧乙烯基团数(EO基团数)、浊点是重要影响参数；蒸汽携带表面活性剂效应、表面活性剂及其水溶液的热稳定性是不确定性影响参数。就影响参数的作用权重而言,相同条件下关键影响参数、重要影响参数和不确定性影响参数的影响权重依次降低。分析比较不同种类表面活性剂水溶液池核沸腾传热强化特性时,在区分表面活性剂电离特性的前提下不仅要考虑影响参数的主次关系,同时也要考虑影响参数的参数值变化方向及变化幅度。(3)鉴于溶液物性准确确定对传热定量分析的重要性和沸腾工况下表面活性剂水溶液表面张力及接触角的现有测定手段的局限性,对沸腾工况下表面活性剂水溶液的表面张力和接触角开展了理论计算研究。基于沸腾工况下表面活性剂的界面吸附传质特征分析,建立了沸腾工况下表面活性剂的界面吸附模型,借助吉布斯(Gibbs)吸附方程,确定了沸腾工况下表面活性剂水溶液表面张力的理论计算式；同时根据固液界面的表面活性剂吸附位状态分析和固汽界面的吸附特征分析,借助润湿方程,确定了沸腾工况下表面活性剂水溶液接触角的理论计算式。根据沸腾工况下表面活性剂水溶液表面张力和接触角的理论计算式,对沸腾工况下的SDS、CTAB、Triton X-114和Triton X-100水溶液的表面张力和接触角进行了理论计算,结果表明：和常温相比,沸腾工况下表面活性剂水溶液的表面张力显著降低；SDS、Triton X-114和Triton X-100水溶液的接触角均小于相同条件下水的接触角,CTAB水溶液则相反；沸腾工况下热流密度对表面张力和接触角的影响体现在较高热流密度范围内。(4)用经典池核沸腾换热关联式对本文实验结果进行了预测,发现经典池核沸腾换热关联式基于的换热模型的片面性使其不能很好地预测实验结果。为开发准确度高、通用性好的表面活性剂溶液池核沸腾换热关联式,在实验研究的基础上分析获取了影响表面活性剂溶液池核沸腾换热的无量纲数,开发了新的无量纲数形式的表面活性剂溶液池核沸腾换热关联式,新建换热关联式计算结果与实验结果吻合良好。更多还原

【Abstract】 The urgency of energy shortages, energy savings and environmental protections requires improving the heat transfer efficiency of boiling heat transfer equipments as much as possible, and the baisc research of boiling heat transfer enhancements thus has important theoretical significance and application value. The boiling heat transfer enhancements with the additives of surfactants have the merits such as small additons, siginificant heat transfer enhancement effect and simple operation, so have aroused public concern around the world and are becoming one of the focuses in the heat transfer scientific research.In this paper, heat transfer enhancement perfromances of nucleate pool boiling with different surfactant additives, two ionic surfactants, sodium dodecyl sulfate(SDS) and cetyltrimethylammonium bromide(CTAB), and two nonionic surfactants, Triton X-114 and Triton X-100, are presented. The main research contents include:the experimental investigations of physical properties, steam carrying effects and nucleate pool boiling heat transfer, the theorectical researches of surface tensions and contact angles of aqueous surfactant solutions under boiling conditions and the establishment of heat transfer correlations of nucleate pool boiling of aqueous surfactant solutions. Based on experimental and theoretical investigations, some achievements with scientific significance and values have been acquired:(1) Physical properties related to boiling heat transfer are investigated based on the selected aqueous surfactant solutions, and the effect law of surfactant species, concentrations and temperature of surfactant solutions on the thermal stability, cloud point, surface tensions, dynamic viscosity and contact angles is achieved. Considering the influence of steam carrying effects on boing heat transfer of surfactant solutions, experimental studies of steam carrying effects during boiling are conducted and the action rules of steam carrying effects on boiling heat transfer enhancement of surfactant solutions are obtained. This work provides a basis for further study the characteristics of boiling heat transfer enhancements of surfactant solutions.(2) Based on the scientific classification of the influence parameters of surfactant solutions boiling heat tranfer, the mechanisms of single parameter and the interactions of all kinds of parameters on boiling heat transfer of surfactant solutions are investigated and the parameters recognition system for nucleat pool boiling heat transfer of surfactant solutions is established. As to the major and minor relationships of influence parameters, concentrations, heat flux, dynamic surface tensions and dynamic viscosity are the key influence parameters, molecular weight, ionic nature, cloud point and ethylene oxide(EO) group number are the important parameters, steam carrying effect and thermal stability are the uncertainty parameters. As to the weight relationships of influence parameters, the weight is becoming lower in the order of key parameters, important parameters and uncertainty parameters at the same conditions. When considering the boiling heat transfer enhancements of different species surfactants, it should be noted that both the major and minor relationships of parameters and the change directions and amplitude of parameter value are to be considered on the basis of the same ionic nature of surfactants.(3) In view of the importance of accurate determination of surfactant solutions physical properties and the limitation of measuring method for surface tensions and contact angles of surfactant solutions under boiling conditions, the theorectical studies of surface tensions and contact angles of surfactant solutions under boiling conditions are carried out. A predicted model of interfacial adsorption is developed based on the mass transfer analysis of interfacial adsorption during boiling of surfactant solutions. Taking account of the Gibbs adsorption equation, analysis of interfacial adsorption of surfactant solutions on solid-liquid and solid-vapor interface and Young equation, the theorectical computation formulas of surface tensions and contact angles under boiling conditions are achieved and the calculation results show that the value of surface tensions under boiling conditions is much lower when comparing with the value of surface tensions under normal conditions. The contact angles of SDS, Triton X-114 and Triton X-100 solutions are lower than water at the same conditions, and the CTAB solutions do the contrast. The influences of heat flux on surface tensions and contact angles exist at high heat flux range.(4) Typical heat transfer correlations for nucleate pool boiling are used to predict experimental data of this paper, but the one-sidedness of heat transfer models in typical correlations leads to the predicted value quite different to the experimental data. Then, a new heat transfer correlations with dimensionless numbers form for nucleate pool boiling of aqueous surfactant solutions is estabished by the regression of nucleate boiling heat transfer experiments data, and the new heat transfer correlations are compared with current available data and experimental data with good cosistency.更多还原