共查询到17条相似文献,搜索用时 46 毫秒
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采用数值模拟方式研究充满了纳米流体的封闭腔内的稳态自然对流。重点分析了纳米颗粒的体积分数,Ra数以及不同类型纳米颗粒对自然对流换热特性的影响。数值模拟结果表明:在纯水中加入纳米颗粒可以显著提高基液的自然对流换热特性;对于给定的Ra数下,随着纳米流体的体积分数增大,纳米流体换热效果显著增强;对于给定的体积分数下,随着Ra数增大,纳米流体的换热强度也随之增大,并且换热机理由热传导为主变为热对流为主;通过Ag,Cu,CuO和Al2O3四种纳米颗粒的对流换热效果比较分析得出,金属Ag和Cu纳米颗粒比金属氧化物CuO和Al2O3的纳米颗粒制备的纳米流体的对流换热效果更好。 相似文献
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对充满Cu-水纳米流体的二维倾斜方腔内的自然对流换热进行了数值研究,研究了纳米颗粒体积份额φ、Ra数和腔体倾角对自然对流换热特性的影响。数值模拟结果表明:在纯水中加入纳米颗粒可以显著提高基液的自然对流换热特性;在一定的腔体倾角φ下,增大Ra均可以强化腔体内的自然对流换热,而且随Ra数的增大,强化效果越强;当Ra=104时,对不同的腔体倾角,纳米流体对换热强度提高的比例大致相当。 相似文献
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采用Fluent软件对封闭腔内纳米流体层流自然对流换热进行了数值模拟研究.重点分析了Ra数和纳米颗粒的体积分数对自然对流换热特性的影响.数值模拟结果表明:在机油中添加多壁碳纳米管(MWCNT)粒子并没有提高基液的自然对流传热特性;对于给定的Ra数下,随着纳米颗粒体积分数的增大,纳米流体的传热特性也随之减弱;对于给定的体积分数,随着Ra数的增大,纳米流体的传热特性显著增强,但纳米流体的传热性能比机油的要弱,且在同一体积分数下随着Ra数的增大,传热性能减弱的程度要减小. 相似文献
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对充满Cu-水纳米流体方腔内的非稳态自然对流换热进行了数值研究。综合研究了不同振荡波形下,纳米颗粒的体积份额和振荡波幅A对自然对流换热的影响。结果表明:在水中添加Cu纳米颗粒可以强化水的自然对流换热;体积份额和振荡波幅A的增大都加强纳米流体自然对流换热,但是不同振荡波形,加强程度不同并提出振荡面积S的概念,即振荡波形与其平均值围成的面积,曲线拟合显示时均努塞尔特数Nu随S增大呈指数曲线上升。 相似文献
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文献采用数值模拟方式研究充满了纳米流体封闭腔内的瞬态自然对流。热边界条件为温度周期性变化的正弦函数。重点分析了在同一Ra下,正弦函数的振幅和频率(或周期)对纳米流体强化对流换热的影响;结果显示:随着热边界的正弦函数的振幅和频率变大,热边界的瞬态Nu数和平均Nu数也越大;同时还观察封闭腔内的漩涡中心,随时间变化周期性发生转移;这些结果对后期研究纳米流体的瞬态自然对流有很大的帮助。 相似文献
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其中μ为粘性系数,p为压力,C_p为定压比热,(g_x,g_y,g_z)为g的x、y、z方向的分量。 若考察竖直环形空腔内流体自然对流换热问题,选取圆柱坐标系,将z轴取得与重力g方向相同,那末,连续性方程、动量方程、能量方程表示成下式: 相似文献
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The radial basis functions (RBFs) have been proven to have excellent properties for interpolation problems, which can be
considered as an efficient scheme for function approximation. In this paper, we will explore another type of approximation
problem, that is, the derivative approximation, by the RBFs. A new approach, which is based on the differential quadrature
(DQ) approximation for the derivative with RBFs as test functions, is proposed to approximate the first, second, and third
order derivatives of a function. The performance of three commonly-used RBFs for some typical expressions of derivatives as
well as the computation of one-dimensional Burgers equation are studied. Furthermore, the proposed method is applied to simulate
natural convection in a concentric annulus by solving Navier–Stokes equations. The obtained results are compared well with
exact data or benchmark solutions.
Received: 27 June 2001 / Accepted: 29 July 2002 相似文献
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Abstract This study is to examine the effects of latent heat transfer associated with liquid film vaporization on heat transfer in the natural convection flows driven by the simultaneous presence of combined buoyancy forces of thermal and mass diffusion. Results are especially presented for an air‐water system under various conditions. The influences of channel length and system temperatures on the momentum, heat and mass transfer in the flow are investigated in great detail. The important role of transport of latent heat of vaporization under the situations of buoyancy‐aiding and opposing flows is clearly demonstrated. 相似文献
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Abstract A numerical analysis has been performed to examine film evaporation on natural convection heat and mass transfer in a vertical pipe. Coupled governing equations for liquid film and induced gas flow were simultaneously solved by the implicit finite difference method. Results for interfacial heat and mass transfer coefficients are specifically presented for ethanol film and water film vaporization. The predicted results indicate that the heat transfer from gas‐liquid interface to the gas flow is predominated by the transport of latent heat in association with film evaporation. The results are also contrasted with those of zero film thickness and show that the assumption of extremely thin film thickness made by Chang et al. [5] and Yan and Lin [19] is only valid for a system with a low liquid Reynolds number Re l1. But as the liquid Reynolds number is high, the assumption becomes inappropriate. 相似文献
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In the present study, the problem of conjugate natural and mixed convection of nanofluid in a square cavity containing several pairs of hot and cold cylinders is visualized using non-homogenous two-phase Buongiorno's model. Such configuration is considered as a model of heat exchangers in order to prevent the fluids contained in the pipelines from freezing or condensing. Water-based nanofluids with Cu, Al2O3, and TiO2 nanoparticles at different diameters () are chosen for investigation. The governing equations together with the specified boundary conditions are solved numerically using the finite volume method based on the SIMPLE algorithm over a wide range of Rayleigh number (), Richardson number () and nanoparticle volume fractions (). Furthermore, the effects of three types of influential factors such as: orientation of conductive wall, thermal conductivity ratio () and conductive obstacles on the fluid flow and heat transfer rate are also investigated. It is found that the heat transfer rate is significantly enhanced by incrementing Rayleigh number and thermal conductivity ratio. It is also observed that at all Rayleigh numbers, the total Nusselt number rises and then reduces with increasing the nanoparticle volume fractions so that there is an optimal volume fraction of the nanoparticles where the heat transfer rate within the enclosure has a maximum value. Finally, the results reveal that by increasing the thermal conductivity of the nanoparticles and Rayleigh number, distribution of solid particles becomes uniform. 相似文献
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Chien-Hsin Chen 《International Journal of Engineering Science》2004,42(7):699-713
The problem of combined heat and mass transfer of an electrically conducting fluid in MHD natural convection adjacent to a vertical surface is analyzed, taking into account the effects of Ohmic heating and viscous dissipation. The resulting governing equations are transformed using suitable transformations and then solved numerically by an implicit finite-difference technique. The solution is found to be dependent on the governing parameters including the magnetic field parameter, the buoyancy ratio between species and thermal diffusion, the Eckert number, the Prandtl number, and the Schmidt number. Effects of these major parameters on the transport behaviors are investigated methodically and typical results are illustrated to reveal the tendency of the solutions. Representative results are presented for the velocity, temperature, and concentration distributions, as well as the local skin-friction coefficient, local Nusselt number, and the local Sherwood number. 相似文献