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Convection in the Rayleigh-Bénard Flow with all Fluid properties variable

Journal of Thermal Science 2011年第5期20卷 454-459页

作者： Athanasios Sassos Asterios Pantokratoras Mechanical Engineering Department Kavala Institute of Technology School of Engineering Democritus University of Thrace

In the present paper, the effect of variable fluid properties （density, viscosity, thermal conductivity and specific heat） on the convection in the classical Rayleigh-Benard problem is investigated. The investigation concerns water, air, and engine oil by taking into account the variation of fluid properties with temperature. The results are obtained by numerically solving the governing equations, using the SIMPLE algorithm and covering large temperature differences. It is found that the critical Rayleigh number increases as the temperature difference increases considering all fluid properties variable. However, when the fluid properties are kept constant, calculated at the mean temperature, and only density is considered variable, the critical Rayleigh number either decreases or remains constant.

关键词： Rayleigh-Benard variable properties onset numerical investigation.

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Effect of turbulence models on predicting convective heat transfer to hydrocarbon fuel at supercritical pressure

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Chinese Journal of Aeronautics 2016年第5期29卷 1247-1261页

作者： Tao Zhi Cheng Zeyuan Zhu Jianqin Li Haiwang National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics School of Energy and Power Engineering Beihang University

A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temperatures varied from 373 K to 663 K, with heat flux rang- ing from 300 kW/m2 to 550 kW/m2. Comparative analyses between predicted and experimental results were used to evaluate the ability of turbulence models to respond to variable thermophysical properties of hydrocarbon fuel at supercritical pressure. It was found that the prediction performance of turbulence models is mainly determined by the damping function, which enables them to respond differently to local flow conditions. Although prediction accuracy for experimental results varied from condition to condition, the shear stress transport （SST） and launder and sharma models performed better than all other models used in the study. For very small buoyancy-influenced runs, the thermal-induced acceleration due to variations in density lead to the impairment of heat transfer occurring in the vicinity of pseudo-critical points, and heat transfer was enhanced at higher temperatures through the combined action of four thermophysical properties： density, viscosity, thermal conductivity and specific heat. For very large buoyancy- influenced runs, the thermal-induced acceleration effect was over predicted by the LS and AB models.

关键词： Buoyancy effect Hydrocarbon fuel Supercritical pressure Turbulence models variable properties

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