Analysis of local thermal non-equilibrium condition for unsteady heat transfer in porous media with closed cells: Sparrow number
Analysis of local thermal non-equilibrium condition for unsteady heat transfer in porous media with closed cells: Sparrow number
复制标题
闭孔多孔介质非稳态传热的局部热非平衡条件分析：麻雀数
DOI：
10.1016/j.ijmecsci.2019.04.022
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发表时间：
2019
影响因子：
7.3
通讯作者：
F. Kuwahara
中科院分区：
文献类型：
--
作者：
C.Y. Wang;M. Mobedi;F. Kuwahara
分析了具有闭孔多孔介质在非稳态传热条件下的局部热不平衡条件。虽然由于浮力效应，流体在封闭孔隙中循环，但封闭孔隙的体积平均速度为零，导致从体积平均控制方程中排除连续性和动量方程。采用平衡热扩散率对体均控制方程进行无量纲化，Sparrow数自动出现在无量纲控制方程中。Sparrow数被解释为整个域的平衡传导热阻与对流热阻之比。当Sparrow数较大时（如1000），对流换热阻力远小于导热阻力，局部热平衡的可能性较大。无量纲控制方程表明，孔隙率、Sparrow数、固体（或流体）无量纲热容和热导率4个无量纲参数对闭孔多孔介质中局部热非平衡状态的预测有重要作用。给出了Sparrow数为1、50、100和500时的局部热不平衡预测图。在此基础上，对以水和空气为工质的闭孔多孔介质进行了孔隙尺度研究。观察到孔尺度和体积平均结果之间的良好一致性。所得到的孔隙尺度的结果支持的体积平均参数研究的结果，也建议的图表预测的局部热非平衡状态。
The local thermal non-equilibrium condition for a porous medium with closed cells under unsteady state heat transfer is analyzed. Although the fluid circulates in the closed pores due to the buoyancy effect, the volume averaged velocity for a closed pore is zero causing excluding of the continuity and momentum equations from the volume averaged governing equations. The volume averaged governing equations are non-dimensionalized by using the equilibrium thermal diffusivity and Sparrow number appears in the dimensionless governing equations automatically. The Sparrow number is interpreted as the equilibrium conduction thermal resistance to the convection thermal resistance for the entire domain. For the high values of Sparrow number (such as 1000), the convection heat transfer resistance is considerably smaller than the heat conduction resistance resulting in high possibility of the local thermal equilibrium. Dimensionless governing equations show that four dimensionless parameters as porosity, Sparrow number, solid (or fluid) dimensionless thermal capacitance and thermal conductivity play important roles on the prediction of the local thermal non-equilibrium state in a closed cell porous medium. A chart for the prediction of local thermal non-equilibrium is presented for Sparrow number of 1, 50, 100 and 500. Furthermore, a pore scale study for a closed cell porous medium with working fluids as water and air is performed. A good agreement between the pore scale and volume averaged results is observed. The obtained pore scale results support the results of the volume averaged parametric study and also the suggested chart for the prediction of local thermal non-equilibrium state.