共查询到20条相似文献,搜索用时 78 毫秒
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利用计算流体力学(CFD)对顺序排列多孔介质小球的三维填充床进行数值模拟。研究填充床内位置及空气流速变化对温度分布、努塞尔数影响,并对多孔介质小球的热回流特性进行分析,揭示填充床内传热机理。结果表明:相比于气-固两相交替存在处,与小球相切处的热的非平衡性更强。最高温度上游的换热强度与下游相比更强烈;当流速增加时,上游的对流换热作用增强,下游变化不大。在热回流过程中,在入口区域对流换热占主导地位,导热和辐射换热作用较弱;在主流场区域,导热占主导地位,其次是辐射换热,对流换热作用最弱。 相似文献
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以硝酸锂熔融盐为流体介质,对封闭方腔内交叉排布的四根热管间的介质自然对流换热进行了数值模拟,研究了热管不同位置和不同瑞利数对方腔内介质自然对流换热特性的影响。结果表明:管间距ε=0.5时,腔体内温度场和流场的对称性开始打破;ε=0.4和0.5时,下管及左右两管产生的热羽流冲刷上管热边界层,使上管局部Nu_φ分别在圆周角φ=180°、φ=280°和φ=80°处出现增强;ε=0.6时,上管不再受下管羽流影响。随着管间距增大,上管平均Nu_m越来越小,下管Nu_m越来越大;ε=0.4~0.6时,管间距对左右两管Nu_m影响很小,但ε=0.7时,左右两管平均换热均明显增强。 相似文献
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埋地原油管道停输期间温降及原油凝固传热模型及数值模拟 总被引:8,自引:0,他引:8
假设原油凝固区域为一固相和液相组成的动态多孔介质区域,建立了土壤、管道能量方程与原油质量、动量和能量方程相互耦合的传热模型,并对埋地原油管道停输温降过程进行了数值模拟.数值模拟结果能够合理解释停输期间温度场、凝固界面和自然对流规律. 相似文献
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采用计算流体力学软件Fluent,对H_2/空气预混气在全填充多孔介质平板微燃烧器内的燃烧过程进行数值模拟.研究了多孔介质导热系数、壁面导热系数、当量比、孔隙率对微燃烧器回热循环的影响规律.模拟结果表明:预热区对流回热效率、多孔介质导热效率与多孔介质导热系数呈正相关趋势;壁面导热系数增大会使预热区对流回热效率下降,壁面对流回热效率上升;预热区对流回热效率、壁面对流回热效率与当量比呈负相关趋势;多孔介质孔隙率是影响回热效率的重要因素,随着孔隙率的增大,预热区对流回热效率下降,壁面对流回热效率上升. 相似文献
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In the present work we investigate the effects of a porous medium on the accelerated flow past a vertical porous limiting surface. The solution of the problem is obtained in closed form by using the Laplace transform technique. 相似文献
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《Applied Thermal Engineering》2002,22(4):449-457
The performance of a proposed porous electric heater is investigated. The porous heater exchanges heat with the working fluid through its large volumetric surface area. As a result, it produces lower surface temperature as compared with the conventional heater for the same imposed heating power. Two mathematical models are presented to describe the thermal behavior of both heaters. Axial diffusion is included in the governing equation of the solid conventional heater. The predictions of both models are compared at different operating conditions where it is found that porous heaters have much better thermal performance than the conventional heaters. 相似文献
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Local Nusselt numbers have been obtained on the porous side and the fluid side of the parallel plate channel. Plots to obtain wall heat transfer directly have been presented. Change in wall heat transfer has been examined to establish that the maximum enhancement in heat transfer occurs at a porous fraction of 0.8 at a Darcy number of 0.001. Correspondingly, the maximum enhancement per unit pressure drop occurs at a porous fraction of 0.7. As Darcy number increases, the porous fraction at which the maximum enhancement in heat transfer occurs decreases. 相似文献
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《International Journal of Heat and Mass Transfer》1987,30(7):1407-1418
Drying of a non-hygroscopic porous slab initially saturated with liquid, up to the time of the first appearance of dried patches (critical time), is studied experimentally using glass beads and convective heating, and analytically using the volume averaged conservation equations for capillary driven liquid flow and empirical constitutive relations. Good agreement has been found between the predicted and measured results and the results show that:
- 1.(a) The surface mass transfer rate depends on the surface saturation. This surface saturation coefficient, which is also a function of both surface geometry and the free stream velocity, is determined experimentally.
- 2.(b) The critical time is a ratio of the internal liquid transport conductance (Péclet number) to the external vapor transport conductance (Biot number).
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Y.Y. Jiang 《International Journal of Heat and Mass Transfer》2002,45(16):3459-3470
Stability of natural convection in porous media differs from that in Newtonian fluid due to the changes of the thermal inertia and the friction. This paper aims to investigate the natural convection and its stability in a toroidal thermosyphon filled with porous media. The flow and temperature fields were numerically simulated and compared with that of Newtonian fluid. The results predicted two obvious local reversal flows near the connections of heating and cooling halves. A one-dimensional model was proposed which described qualitatively the occurring and stability of the thermal convection. The model suggested that the flow stability depends largely on the Prandtl number. The global flow can probably be chaotic only if the Prandtl number is finite. Contradictions of the conclusions drawn by different researchers were also discussed. 相似文献
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This paper describes an experimental study on natural convection along a vertical porous surface consisting of a bank of parallel plates with constant gaps. Compared with a smooth surface, the heat transfer for a porous surface with streamwise gaps is somewhat enhanced owing to enthalpy transport due to flow within the gaps and that with spanwise gaps is enhanced due to the leading- and trailing-edge effects of solid-phase micro surfaces. Observations show that no clear transition to turbulent flow occurs at a critical Rayleigh number for a smooth surface and that the boundary layer oscillates with a dominant frequency at higher Rayleigh numbers. The dominant frequency for a porous surface is nearly the same as that for a smooth surface. This fact obviously indicates that the oscillations of natural convection are almost independent of the porous structure of the heating surface and are mainly dependent on the behavior of the outer boundary layer. © 1998 Scripta Technica. Heat Trans Jpn Res, 26(6): 385–397, 1997 相似文献
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Irfan Anjum Badruddin Abdullah A.A.A. Al-Rashed N.J. Salman Ahmed Sarfaraz Kamangar K. Jeevan 《International Journal of Heat and Mass Transfer》2012,55(23-24):7175-7187
The current study is focused to investigate the natural convective heat transfer characteristics in a porous square annulus. Finite element method is used as a tool to simplify the partial differential equations that govern the heat and fluid flow characteristics inside the porous medium. A simple three noded triangular element is used to divide the porous domain into smaller segments known as elements. The algebraic set of equations resulting from the finite element equation are assembled into a global matrix and then solved iteratively to get the solution variables. Thermal equilibrium as well as non equilibrium in porous domain is considered. The effect of various geometric and physical parameters are investigated. The boundary conditions are such that the inner walls of the annulus are heated isothermally to temperature Th, and the outer surfaces are exposed to cool temperature Tc. The width ratio defined as the ratio of hollow portion to the length of the cavity is varied from 0.125 to 0.875. Results are discussed with respect to width ratio, Rayleigh number, radiation parameter and viscous dissipation parameter. 相似文献
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Present paper is performed to investigate the heat and exergy transfer characteristics of forced convection flow through a horizontal rectangular channel where open-cell metal foams of different pore densities such as 10, 20 and 30 PPI (per pore inches) were situated. All of the bounding walls of the channel are subjected to various uniform heat fluxes. The pressure drop and heat transfer characteristics are presented by two important parametric values, Nusselt number (NuH) and friction factor (f), as functions of Reynolds number (ReH) and the wall heat flux (q). The Reynolds number (ReH) based on the channel height of the rectangular channel is varied from 600 to 33?000, while the Grashof number (GrDh) ranged from approximately 105–107 depending on q. Based on the experimental data, new empirical correlations are constructed to link the NuH. The results of all cases are compared to that of the empty channel and the literature. It is found that the results are in good agreement with those cited in the references. The mean exergy transfer Nusselt number (Nue) based on the ReH, NuH, Pr and q for a rectangular channel with constant heat flux is presented and discussed. 相似文献