Study Of Heat Transfer And Flow In Porous Media With Phase Change For Some Applications

Problems involving multiphase flow, multicomponent transport and heat transfer in porous media arise in a number of scientific and engineering disciplines. Those important technological areas include soil sciences, oil reservoir engineering, groundwater contamination and remediation, heat pipe technologies, drying processes, particulate materials processing, trickle bed reactors, geothermal reservoirs and so on. For many decades, the traditional multiphase flow models based on the generalized Darcy's law. However, Darcy's law is limited to the flow process of small Raleigh number. And these models are always cumbersome and computationally demanding when applied to predicting multiphase flow and transport. This paper is to develop a novel model for the exploration of multiphase flow and transport in porous media. This new model bases on classifying and analyzing various kinds of transport theory in unsaturated porous media, applies continuum medium dynamics and local volume averaging technique, and considers a larger number of transport details than others, therefore it is more rigorous in describing the heat and mass transport phenomena in unsaturated media.Because of involving more transport mechanisms, this model is able to fit more conditions than others. And the governing equations are similar in form and can be cast into one general form, which makes it more suitable for numerical implementation. In this paper, the present model is adopted to numerical simulate the transport process in porous media for two major industrial areas. One area contains the multiphase transport in relation to soil sciences, building material and energy saving, and drying processes, for example a multiphase flow including liquid, vapor and incondensable gas. The most important character of such a problem is that the vapor makes not only a bulk motion under the pressure gradient with the whole gas phase together, but also a diffusive motion relativing to the incondensable gas. The other area concerns twofers flow and heat transfer in porous media as widely encountered in energy conversion and electronics cooling. The character of this problem is that the fluid flow always companies with a rather large heat flux, and is in a forced convection situation. The temperature of the saturated liquid in the porous wick becomes high gradually by the heat flux until phase change happens. If the imposed heat flux is large enough, a vapor blanket formed and then the porous wick is divided into three regions: saturated liquid region, two-phase region and saturated vapor region.For the former case, the nature convection behavior in a rectangular enclosure packed with porous media is numerical calculated and discussed as a typical example. The results show that the heat transfer rate of enclosure at high Darcy is effected greatly by the properties of heat and mass transfer of the fluid, Darcy effect and conductivity ratio. And the results also show that Darcy-effect produces great effect on the heat transport of enclosure only at low Rayleigh number. In addition, a novel solar building energy saving system is posed for the first time in this paper, which enhances heat transfer through the utilization of unsaturated porous media with phase change. Such a system costs only low quality and low-density solar energy, has high heat transport capability, and therefore is good at saving energy. Through the numerical simulation for the flow of working media in evaporator porous bed, isotherm patterns and evaporation rate field for the different boundary conditions are acquired. According to the results, keeping the inner wall with constant temperature is favored to absorb solar energy, while keeping the inner wall with adiabatic condition is favored to enhance the system heat efficiency. To the problem of tow-phase flow in porous media, the traditional mathematic models are analyzed and discussed. Then basing on the theory mentioned above, a new two-phase three-layer model is built. Using this new three-layer model, a numerical simulation for th...