底部加热的复合多孔介质热-流耦合场非线性特性

针对非线性流动传热受底部加热模型骨架的影响及分叉、震荡点的非线性解析解难求的问题,采用数值模拟及实验的方法对底部加热的复合多孔介质热流耦合传热过程进行数值求解和温度测试。构建底部加热的复合多孔介质热-流耦合传热的三维模型;采用SIMPLE算法对控制方程组进行QUICK格式离散求解,并在底部加热实验台上对测点进行温度采集。在小Ra工况下,揭示了复合多孔介质内存在热流分布分层特性及确定了非线性分叉、震荡解的特征值。数值结果表明:热流场分布对初始场依赖敏感,低Ra情况下三维腔体内热流场表现出稳定的二维性质;与单层多孔介质相比,复合多孔介质内存在热流分布分层的非线性特性;非线性分叉、震荡点对应的临界Ra依赖复合多孔介质骨架高度比,高度比越大(强导热、高阻力多孔介质区所占高度越大),静态分叉及震荡所对应的临界Ra越小,越早表现出分叉、震荡等非线性特性;改变复合多孔介质内高度比可以重新优化热流场分布,实现削弱或强化传热。

Nonlinear characteristics of heat-fluid coupling field heated from below in composite porous media

In view of the phenomenon that the nonlinear flow and heat transfer are influenced by skeleton of the model heated from below,and the problem that nonlinear analytical solutions to bifurcation and oscillation are hard to get,numericalsimulation and experiment on the heat-fluid coupling process in the composite porous media heated from below are adopted to get the numerical solution and temperature tests.Three-dimensional model of the composite porous media heated from below is constructed.SIMPLE algorithm with QUICK scheme is used to discrete solutions for control equations and the temperatures of the measure points are tested in the experiment table heated from below.For the condition of small Ra,the phenomenon that there is thermal stratification in composite porous medium,and the characteristic values of nonlinear bifurcation and oscillation are obtained.The numerical results show that:the hierarchical distribution of thermal fluid field is sensitively dependent on initial field;thermal fluid field shows stable two-dimensional nature in the three-dimensional cavity,under the influence of small Ra.Compared with single porous media,there is the hierarchical distribution of thermal fluid field in the composite porous media;the critical values of Ra at the point of nonlinear bifurcation and oscillation rely on height ratio of keleton;the bigger height ratio is (the taller the height of porous medium which has strong thermal conductivity and big high resistance is),the critical Ra is smaller,the nonlinear characteristics,such as bifurcate and oscillation,are shown earlier.Changing the height ratio in composite porous media can optimize the distribution of thermal fluid field,to achieve weaken or strengthen heat transfer.