基于多相流模型的腔体内纳米流体自然对流换热数值模拟

Numerical Simulation of Natural Convective Heat Transfer Characteristics of Nanofluids in an Enclosure Using Multiphase-Flow Model

运用多相流混合模型和单相流模型模拟了纳米流体在封闭腔体内的自然对流换热特性,将模拟结果与相应的实验值进行对比,分析了瑞利数、格拉晓夫数和纳米颗粒体积分数等物理量与努塞尔数的关系;同时,对比分析了纳米流体和纯水在水平与垂直中心截面的速度分布,以及封闭腔体内流体的温度场及流场.结果表明:基于N-S方程的单相流模型所得努塞尔数变化曲线与水的努塞尔数曲线较吻合,但不能反应纳米流体的换热特性;而基于多相流混合模型所得努塞尔数变化曲线与相应的实验结果较吻合;纳米颗粒的添加能够显著增强封闭腔体内的流体运动,有利于强化封闭腔体内流体的能量传输,起到了对流换热作用.

The natural convection heat transfer and flow characteristics of nanofluids in an enclosure were numerically simulated using the multiphase-flow model and single phase model respectively. The simulated results were compared with the experimental results from the published papers to investigate the applica- bility of these models for nanofluids. The multiphase-flow model is mixture model. The effects of various parameters such as Rayleigh number, Grashof number and volume concentration of nanoparticles on the heat transfer and flow characteristics were investigated and discussed. Comparisons of the central velocity profiles between nanofluid and water for various Gr numbers were studied as well. In addition, streamlines contours and isotherms for different volume concentration were analyzed. The results show that a great de- viation exists between the simulated results based on single phase model and experimental data on Nu-Ra heat transfer curve, which indicates that the simulation based on single phase model and N-S equations cannot reflect the heat transfer characteristic of nanofluid, while the simulated results using multiphase- flow model have good agreement with the experimental data of nanofluid, which means that the multi- phase-flow model is more suitable for the numerical study of nanofluid. Moreover, nanoparticles can significantly enhance the motion of fluid in the enclosure, which is in favor of strengthening the energy trans fer in fluid. Besides, nanofluids also show the characteristic of strengthening the convection in the enclo sure.