内插多孔介质微通道热沉的数值模拟

以水为流动介质,在微通道内添加堆叠金属丝网多孔介质,采用局部非热平衡假设和双能量方程模型,分析了内插不同目数金属丝网的微通道在层流状况下的传热与阻力特性,并采用数值计算方法对微通道热沉进行了数值模拟。结果表明,在微通道内插入多孔介质能显著提高热沉的对流换热系数、降低加热面平均温度,但阻力增加较大,且当插入的金属丝网目数为100目时,微通道热沉的对流换热系数较大,与填充其他目数金属丝网相比阻力增加较小。     

壁面覆盖部分多孔介质方腔自然对流流动的数值模拟

多孔介质壁面封闭腔体的自然对流在生产实际中有重要的应用。针对左侧部分多孔介质壁面方形封闭腔体,基于有限元法对封闭腔体的自然对流换热进行了数值模拟,得到了在不同Ra、孔隙率条件下腔体内空气的温度分布、速度分布。结果表明:随着Ra的增大,腔体内的流场及温度场发生了明显的变化,多孔介质壁面孔隙率的变化对腔体的流动换热的影响很小。     

幂律流体饱和多孔介质通道中的粘性耗散效应

针对Darcy-Brinkman-Forchheimer流动模型,分析了幂律型非牛顿流体在填充多孔介质平板通道中强迫对流传热过程充分发展的黏性耗散效应,并比较了三个不同的黏性耗散项Darcy项、Al-Hadhrami项和Forchheimer项对流动传热率的影响。推导出了无量纲轴向流速分布和无量纲温度分布的计算表达式,并在恒热流边界条件下,利用经典Runge-Kutta法进行数值求解。模拟结果表明,布林克曼数Br、达西数Da、综合惯性参数F和幂律指数n等重要参数对无量纲温度分布有着较大的影响,同时发现不同的黏性耗散效应对流动传热特性也有着重要的影响。     

混凝土多孔介质等温吸湿过程的数值模拟

分析了含湿多孔介质吸湿的主要机理，根据介质吸湿过程中的热湿平衡建立了其吸湿过程的一维数学模型。采用控制容积法及时间显式积分方案对方程进行了数值计算。计算结果表明多孔介质在等温吸湿过程中存在不稳定和相对稳定两个阶段。吸湿处于不稳定阶段时温度梯度势和含湿量梯度势相互作用；吸湿处于相对稳定阶段时仅存在含湿量梯度势。同时比较了轻质混凝土、半轻质混凝土、粘土实心砖三种材料的吸湿性能。     

内燃机气缸壁面传热的数值模拟

本文建立了内燃机气缸壁面传热过程的数学模型,传热系数采用欧洲广泛使用的Ｗｏｓｃｈｎｉ、Ｗｏｓｃｈｎｉ－Ｈｕｂｅｒ、Ｈｏｈｅｎｂｅｒｇ和Ｂａｒｇｅｎｄｅ提出的经验公式计算。通过ＭＯＳＥＳ－Ⅱ内燃机工作过程数值模拟计算程序进行数值模拟,并将计算结果与试验结果进行比较。     

交叉耦合及壁面多孔效应对室内VOCs传热传质的影响

交叉耦合扩散效应及室内壁面对材料内部的VOCs在多物理场环境中的传热传质有很大影响;采用有限元法进行求解,分析了在温度梯度、水蒸气湿度梯度及VOCs浓度梯度共存时,多孔壁面达西数、综合浮力比、热附加扩散效应准则数和质附加扩散效应准则数对室内壁面中VOCs传热传质的直接影响。正确掌握这些影响规律对改善室内空气品质,营造一个真正舒适的室内环境有重大的意义,研究结果可以为对实际工程提供必要的理论依据。     

多孔小颗粒对流干燥的数值模拟

从毛细多孔物料的微观结构出发,建立了多孔小颗粒在干燥过程中热质传递规律的数学模型.采用全隐式有限差分法求解得到的模拟结果与实验数据吻合较好.数值模拟表明,土霉素滤饼等速干燥时间较短,降速干燥后干燥速率急剧下降;热空气流速对等速干燥速率影响较大,对降速干燥速率影响较小;提高干燥温度,减少颗粒直径,可以缩短干燥时间;孔隙分布期望值大、标准方差小的多孔物料,干燥容易完成.     

多孔介质燃烧室内湍流流动及燃油喷雾的数值模拟

以多孔介质发动机为背景,用数值模拟方法考察气缸内加入多孔介质蓄热体后对燃烧室内湍流流场及混合气形成的影响.计算基于Antohe和Lage的适用于多孔介质的k-e模型,其中引入了Darcy项和Forchheimer项.对燃油喷雾在自由空间和多孔介质组成的燃烧室内的流场进行了数值计算.计算结果表明,多孔介质对燃油液滴与空气的混合过程具有重要的影响,多孔介质内的流场作为一个局部流场和整个燃烧室内流场发生相互作用.Darcy项和Forchheimer项均对湍能起阻尼作用,从而降低多孔介质内的湍能水平.这种阻尼作用随多孔介质渗透率的减小而增大.为检验数值模型的合理性,针对文献中的实验条件进行了相应的数值计算,计算结果与实验结果吻合良好.     

两层多孔介质燃烧器的数值模拟

通过一维数值模拟研究了预混气体在两层多孔介质燃烧器内的燃烧特性,着重研究两层多孔介质燃烧器中的超绝热燃烧和火焰的稳定区域。结果表明,预混气体在两层多孔介质内可以发生一定程度的超绝热燃烧,贫燃极限可以扩展到0.45。两层多孔介质能够在较宽的流速范围内将火焰稳定在它的交界面上。数值预测的最小和最大火焰传播速度与实验取得了相同的趋势,其火焰传播速度至少是自由空间中的3倍。     

伞喷油雾与热多孔介质相互作用的数值模拟

为深入认识多孔介质发动机中均匀混合气的形成,用改进的KIVA-3V详细模拟了伞喷油雾与热多孔介质之间的相互作用．在KIVA-3V中增加了油滴碰撞热多孔介质壁面的碰撞模型、传热模型．为检测数值模型的合理性,在Senda等人的实验条件下进行了数值计算．油束碰壁后油滴和油蒸气分布的数值计算结果与实验结果吻合较好．在简化多孔介质结构的基础上和不同的环境压力及喷雾锥角时,模拟了伞喷油雾与热多孔介质的碰撞过程．计算结果表明,伞喷油雾的喷雾锥角及空间压力对油滴在多孔介质中的分布有着很大的影响,在多孔介质厚度一定时,通过调节这些参数,能够形成均匀混合气．     

Numerical and experimental investigation of heat and mass transfer in unsaturated porous media with low convective drying intensity

The heat and mass transfer in an unsaturated wet cylindrical bed packed with quartz particles was investigated theoretically and experimentally for relatively low convective drying rates. The medium was dried by blowing dry air over the top of the porous bed which was insulated by impermeable, adiabatic material on the bottom and sides. Local thermodynamic equilibrium was assumed in the mathematical model describing the multi‐phase flow in the unsaturated porous medium using the energy and mass conservation equations for heat and mass transfer during the drying. The drying model included convection and capillary transport of the moisture, and convection and diffusion of the gas. The wet and dry regions were coupled with a dynamic boundary condition at the evaporation front. The numerical results indicated that the drying process could be divided into three periods: the initial temperature rise period, the constant drying rate period, and the reduced drying rate period. The numerical results agreed well with the experimental data, verifying that the mathematical model can evaluate the drying performance of porous media for low drying rates. ©2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(5): 290–312, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20205     

Forced Convective Heat Transfer in a Porous Plate Channel

INTRODUCTIONHeattransferenllancen1enttechniquesplayaveryimportantroleintllermalcontroltechnologies1lsedwithnlicroelectronicchips,powerfullasermirrors,aerospacecraft,thermalnuclearfusion,etc.Itiswidelyrecognizedthattl1eheattransfercanbein-creasedbyil1creasingthesurfaceareaincontactwiththecoolant.TuckermanandPease[1,2]pointedoutthatforlaminarflowinconfinedchannels,theheattransfercoefficientisinverselyproportionaltothewidthofthechannelsincethelimitingNusseltnum-berisconsta11t.Theybuiltawate…     

Fully developed natural convection heat and mass transfer in a vertical annular porous medium with asymmetric wall temperatures and concentrations

This work examines the effects of the modified Darcy number, the buoyancy ratio and the inner radius-gap ratio on the fully developed natural convection heat and mass transfer in a vertical annular non-Darcy porous medium with asymmetric wall temperatures and concentrations. The exact solutions for the important characteristics of fluid flow, heat transfer, and mass transfer are derived by using a non-Darcy flow model. The modified Darcy number is related to the flow resistance of the porous matrix. For the free convection heat and mass transfer in an annular duct filled with porous media, increasing the modified Darcy number tends to increase the volume flow rate, total heat rate added to the fluid, and the total species rate added to the fluid. Moreover, an increase in the buoyancy ratio or in the inner radius-gap ratio leads to an increase in the volume flow rate, the total heat rate added to the fluid, and the total species rate added to the fluid.     

Electrochemical experimental method for natural convective heat and mass transfer in porous media

Natural convection driven by combined thermal and solutal buoyant forces in a fluid-saturated porous enclosure was studied experimentally. An electrochemical method was employed to establish the concentration gradients. The inside temperature profiles and heat and mass transfer coefficients on the vertical walls were determined experimentally. The effects of dimensionless parameter Ra, Le, N on flow, heat, and mass transfer are discussed in detail. © 1999 Scripta Technica, Heat Trans Asian Res, 28(4): 266–277, 1999     

Analysis of MHD micropolar nanofluid flow and heat transfer between a porous plate and a nonporous plate filled with porous medium

This article presents an analytical study on magnetohydrodynamic micropolar nanofluid flow through parallel, coaxial discs filled with a porous medium with uniform blowing from the upper plate. Three different types of nanoparticles, namely copper, aluminum oxide, and titanium dioxide are considered with water and used as base fluids. The governing equations are solved via Differential Transformation Method. The validity of this method has been verified with the results of numerical solution (fourth‐order Runge‐Kutta scheme). The analytical investigation is carried out for different governing parameters. The results indicate that skin friction coefficient has a direct relationship with Hartmann number and the micropolar parameter. It is also found that Nusselt number is increased with increment in Prandtl number and Eckert number. Additionally, this analysis concluded that an increase in volume fraction of nanofluid increases the Nusselt number on the top plate and decreases it on the lower plate.     

Combined convection heat transfer in a channel with two ribs attached to one wall

Two-dimensional calculations were performed for combined convection heat transfer in a channel with two ribs attached to one wall, following a previous study on the forced convection case without buoyancy. The flow is heated from the surfaces of both ribs and the present study dealt with the two cases of buoyancy-assisted flow and buoyancy-opposing flow. The effect of Reynolds number, Re_L, and modified Richardson number, Ri^*, was examined keeping the space between ribs, σ, and blockage ratio, τ, constant (σ = 3.0, τ = 0.5). Increasing the magnitude of buoyancy, unsteady flows predicted by the present calculations are stabilized in both cases. Serious deterioration of Nusselt number on the second rib suddenly occurs in a certain range of Ri^* due to the flow stabilization. This is because flow unsteadiness plays an important role for heat transfer enhancement as was described in a previous study. However, in buoyancy-assisted flow, a similar deterioration of Nusselt number also appears on the second rib even if flow remains steady. This is caused by the disappearance of a strong rotating flow which exists in the cavity between both ribs and keeps the fluid in the cavity cooler. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 379–394, 1999     

Effect of double stratification on mixed convection heat and mass transfer from a vertical surface in a fluid‐saturated porous medium

This paper presents the mixed convection heat and mass transfer near a vertical surface in a stratified porous medium using an integral method. The conservation equations that govern the problem are reduced to a system of coupled non‐linear ordinary differential equations, which is then reduced into a single algebraic equation using exponential profiles for the temperature and concentration. The results for heat and mass transfer rates in terms of Nusselt and Sherwood number are presented for a wide range of governing parameters like the buoyancy ratio (N), Lewis number (Le), flow driving parameter (Ra/Pe), in addition to both thermal and solutal parameters (S and R). The results indicate that the stratification effects have considerable influence on both the heat and mass transfer rates. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20300     

Analysis of flow and heat transfer characteristics of porous heat-storage wall in greenhouse

The flow and heat transfer characteristics of porous heat-storage wall in greenhouse are studied by using the one-dimensional steady energy two-equation model for saturated porous medium. The results show that the heat exchange between the air and the solid matrix of the porous heat-storage wall depends upon the inlet air velocity, the porosity and the permeability of porous medium, and the thermal conductivity of the solid matrix. Because the incidence of solar radiation on the porous heat-storage wall is not uniform, the new composite porous solar wall with different porosity is proposed to reduce the disadvantageous effect. __________ Translated from Journal of Engineering Thermophysics, 2008, 29(2): 284–286 [译自: 工程热物理学报]     

Mechanism and mathematical model of heat and mass transfer during convective drying of porous materials

Based on classical analysis and conclusive comments about various kinds of drying models, a rigorously formulated and comprehensive theoretical model is established to describe heat and mass transfer during constant rate and falling rate periods in convective drying of porous materials. The concept of iterative correction is introduced, and a corresponding numerical method is developed for the moving boundary problem in numerical simulations of drying processes. The calculation results for the drying of bricks show that the model presented is more precise than other models. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 337–351, 1999     

Combined heat and mass transfer in natural convection flow from a vertical wavy surface in a power-law fluid saturated porous medium with thermal and mass stratification

This work studies the coupled heat and mass transfer by natural convection near a vertical wavy surface in a non-Newtonian fluid saturated porous medium with thermal and mass stratification. The surface of the vertical wavy plate is kept at constant wall temperature and concentration. A coordinate transformation is employed to transform the complex wavy surface to a smooth surface, and the obtained boundary layer equations are then solved by the cubic spline collocation method. Effects of thermal and concentration stratification parameters, Lewis number, buoyancy ratio, power-law index, and wavy geometry on the important heat and mass transfer characteristics are studied. Results show that an increase in the thermal and concentration stratification parameter decreases the buoyancy force and retards the flow, thus decreasing the heat and mass transfer rates between the fluid and the vertical wavy surface. It is shown that an increase in the power-law index, the thermal stratification parameter, or the concentration stratification parameter leads to a smaller fluctuation of the local Nusselt and Sherwood numbers with the streamwise coordinate. Moreover, the total heat transfer rate and the total mass transfer rate of vertical wavy surfaces are higher than those of the corresponding smooth surfaces.