共查询到19条相似文献,搜索用时 234 毫秒
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为研究柴油机微粒捕集通流式过滤体多孔介质中的非线性流动特性,通过将多孔过滤材料复杂结构简化成规则布置的球形通道,直接以过滤材料的孔隙率和孔隙直径等为基本参数,从流体的动量方程出发,经过推证,提出了一种计算通流式过滤体非线性流动特征的理论模型.模型既考虑了流体流过过滤介质时骨架表面的摩擦阻力作用,也考虑了过滤介质骨架的形状阻力,得到了适用于通流式过滤体非线性流动关系式及式中有关系数的确定方法.另外,针对4种不同结构的陶瓷泡沫过滤体进行了试验验证,结果表明理论计算与试验结果有良好的一致性,从而证实了 F-w 公式对通流式PDF过滤体的适用性,可以为通流式DPF的设计和优化提供理论依据和参考. 相似文献
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含甲烷水合物多孔介质渗透性的实验研究 总被引:2,自引:0,他引:2
为研究多孔介质中甲烷水合物对其渗透性的影响,开发了一套适合在该条件下测量渗透性的实验装置。研究了多孔介质孔隙度与渗透率的关系;用BZ-01、BZ-02玻璃砂模拟多孔介质进行了渗透率测量实验,测试了不同甲烷水合物饱和度下多孔介质渗透率的变化情况。结果表明,多孔介质中甲烷水合物的存在会导致其渗透率急剧下降,饱和度-渗透率曲线呈指数分布。根据实验数据拟合出了渗透率随饱和度变化的经验公式,并将实验数据与渗透率模型进行了比较,发现在实验条件下生成的甲烷水合物符合平行毛细管模型,水合物占据毛细管中心,多孔介质中的流动形成环状流。 相似文献
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针对接触型和分隔型多孔介质太阳能集热组合墙系统,分析了太阳辐射及环境温度变化时,组合墙内传热与流动变化.多孔介质太阳能集热组合墙中,多孔介质起半透明隔热体和蓄热体的作用.多孔介质集热层的孔隙率、粒径、材料热导率和多孔介质集热层在组合墙中的位置对系统的采暖效果影响较大. 相似文献
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多孔介质燃烧室内湍流流动及燃油喷雾的数值模拟 总被引:1,自引:0,他引:1
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. 相似文献
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为研究LNG闪蒸气在低温储存环境下的吸/脱附特性及热效应,基于格子玻尔兹曼方法建立了多孔介质内闪蒸气流动传热传质的数值模型,并考虑闪蒸气在多孔介质表面的吸附作用和内部微晶孔扩散作用及传热效应,分析不同孔隙率多孔介质材料的闪蒸气低温吸附热力学特性。结果表明:闪蒸气的吸附作用使多孔介质温度明显升高,吸附速率与孔隙率呈负相关,吸附量和温度变化受孔隙率影响较小;环境热量驱动下闪蒸气从多孔介质中脱附,通过脱附吸热抵消了约45%的外部漏热侵入,且随着孔隙率增大闪蒸气脱附吸热效应增强。 相似文献
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通过对刷式密封刷丝束中泄漏流动特点的分析,把刷丝束当作多孔介质来处理,有效简化刷丝束中复杂的泄漏流动,建立了刷丝束中多孔介质的泄漏流动模型。刷式密封内泄漏流动的特性采用的是基于多孔介质模型Reynolds-averaged Navier-Stokes方程的数值计算方法进行研究的。计算和分析了不同转速、不同压差和不同孔隙率下的泄漏流量。计算结果表明:在相同的孔隙率下,压差越大泄漏量越大;在相同的压差下,孔隙率越小,泄漏量越小;刷式密封的泄漏量与轴的转速无关。通过数值计算和实验结果的对比,两者数据吻合较好,验证了采用多孔介质模型模拟刷式密封刷丝束的可行性。 相似文献
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采用基于改进Darcian多孔介质模型的Reynolds-Av-eraged Navier-Stokes方程求解技术,用数值模拟的方法分析了在一定径向间隙条件下压比和刷丝束厚度对刷式密封泄漏流动特性的影响规律。根据发表的刷式密封泄漏量试验数据,确定了刷丝束多孔介质的渗透率系数。利用所确定的刷丝束多孔介质渗透率系数,分别计算了在一定径向间隙条件下7种压比和5种刷丝束厚度时某轴端刷式密封的泄漏量和泄漏流动形态。计算结果表明,压比和刷丝束厚度均影响刷式密封的泄漏量,在一定压比条件下,泄漏量随着刷丝束厚度的增加而减小;在一定刷丝束厚度条件下,泄漏量随着压比的增加而增加。因为刷式密封泄漏量与压比和刷丝束厚度近似成线性变化,所以压比和刷丝束厚度对刷式密封内泄漏流动形态的影响可以忽略。 相似文献
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In this study, the gas transfer characteristics for porous materials with liquid water are studied, and the methods for calculating relative permeability and relative diffusivity of gas in a porous material by considering its pore size distribution are proposed. The calculation results show not only that the saturation has an impact, but also that the pore size distribution of the gas diffusion layer should be considered when calculating the relative diffusivitiy of a porous material with liquid water. In addition, the relative diffusivity calculated by the simplified formula proposed in this paper is closer to the experimental result than that obtained by other researchers. Moreover, the formulas proposed in this paper explain why porous materials with different pore size distributions have similar relative diffusivity obtained through experments by other researchers. 相似文献
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Marcelo J. S. de Lemos Edimilson J. Braga 《Numerical Heat Transfer, Part B: Fundamentals》2018,73(2):78-93
The aim of this work is to estimate the permeability of porous enclosures for numerical solutions of turbulent natural convection in a square cavity. The motivation is that available permeability correlations were proposed based on force rather than natural convection through permeable media. Although commonly seen as a medium property, permeability is measured with a flow through the permeable structure and, as such, its value may carry a flow type dependency. Here, it is assumed that a fixed amount of a solid conducting material is distributed within the cavity and two mathematical models are used and compared when calculating the cavity Nusselt number. First, a porous-continuum model is considered based on the assumption that the solid and the fluid phases are observed as a single medium, over which volume- and time-averaged transport equations apply. Second, a continuum model is used to solve local momentum and energy equations, in both the solid and void spaces, through a conjugate heat transfer solution. The average Nusselt number at the hot wall obtained from the porous-continuum model for several Darcy numbers are compared with those obtained with the continuum model using up to N?=?1,024 obstacles within the cavity. When comparing the two methodologies, this study shows that the average Nusselt number calculated by each approach differs by as much as 32% when the number of obstacles N is increased to 1,024. Based on that, an adjustment on the used correlation for calculating the porous medium permeability is proposed to match the Nusselt numbers calculated with the two models. Results indicate that the use of the new correlation gives results for Nu that differ less than about 4% for the range 4?N?1,024. 相似文献
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Jianjun Liu Yoshihiko Sano Akira Nakayama 《International Communications in Heat and Mass Transfer》2009
A simple mathematical model has been proposed so as to determine the equivalent permeability of fractured porous media. The model consists of square blocks placed in an array with vertical and horizontal fractures between the blocks. An analytical expression valid for all macroscopic flow directions has been derived for the equivalent permeability of the fractured porous media, assuming a horizontal flow through the blocks placed in a porous medium. The analytical expression agrees well with the existing equations and also with the microscopic numerical results carried out using a unit structure with periodic boundary conditions. The foregoing two-dimensional model has been extended to a three dimensional case in which the cubic rocks are arranged in a cubic array. The resulting three-dimensional analytical expression for the equivalent permeability is found to agree very well with both existing formula and microscopic numerical simulation. 相似文献
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多孔介质中预混火焰燃烧速率的预示 总被引:9,自引:0,他引:9
本文提出了一种预估多孔介质中预混火焰燃烧速率的方法。在构成气,固两相合一模型的基础上,用光学厚极限条件下的扩散近似法简化其中的热辐射项,从而由基本能量方程导出计算火焰传播速度的迭代关系式,其中包含综合多孔介质传导和辐射的等效导热系数。然后应用此数值迭代法,分别计算出在多孔泡沫陶瓷中层流预混火焰及无多孔介质存在的自由火焰的燃烧速率。 相似文献
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目前对波形板汽−水分离装置的研究多集中于结构参数和入口参数的分析,而从其材料特性角度探讨提高分离效果的研究鲜有报道。以去离子水为介质,探讨了泡沫铜多孔材料孔隙率、有效半径以及浸润性对其渗透特性的影响。将修正后的弯毛细管模型与达西定律相结合,建立了泡沫铜渗透率、孔隙率以及有效半径之间的定性关系,即随着泡沫铜孔隙率和有效半径的增加,其渗透性能逐渐增强,这一结论与实验结果符合良好。此外,通过对泡沫铜材料进行浸润改性,分析了浸润性对其渗透性能的影响,结果发现,随着表面能的提高,泡沫铜的渗透性能逐渐增强。 相似文献
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Mingchao Liang Yaming Liu Boqi Xiao Shanshan Yang Zhankui Wang Hongmei Han 《International Journal of Hydrogen Energy》2018,43(37):17880-17888
An analytical model is presented for the transverse permeability of gas diffusion layer (GDL) based on an ordered array of parallel charged circular cylinders at the steady state. The formula of calculating the permeability of the transverse direction is given by solving the fluid momentum equation in a unit cell. In the present approach, the proposed model is explicitly related to the porosity and fiber radius of fibrous porous media, the zeta potential, and the physical properties of the electrolyte solution. Besides, the effects of these parameters (the porosity, unit cell aspect ratio, fiber radius, and molar concentration) on the transverse permeability are discussed detailedly. The model predictions are compared with the previous studies in the available literature, and good agreement is found. 相似文献
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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. 相似文献