Research On Nucleate Pool Boiling Heat Transfer Enhancement Of Aqueous Surfactant Solutions

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.