共查询到19条相似文献,搜索用时 296 毫秒
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利用CFD软件数值研究了颗粒三维有序堆积多孔介质的对流换热问题. 采用颗粒直径分别为14 mm,9.4 mm和7 mm的球形颗粒有序排列构成多孔介质骨架,在多孔骨架的上方有一恒热流密度的铜板. 采用流固耦合的方法研究了槽通道内温度分布和局部对流换热系数的分布以及对流换热的影响因素. 研究结果表明:热渗透的厚度和温度边界层的厚度在流动方向上逐渐增大,并且随流量的增加而减小;当骨架的导热系数比较高时,对流换热随颗粒直径的减小而略有增大;对流换热系数随聚丙烯酰胺溶液浓度的增大而减小,黏性耗散减弱了对流换热.
关键词:
多孔介质
温度场
局部对流换热系数
数值模拟 相似文献
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流体在微多孔介质内对流换热实验研究 总被引:1,自引:0,他引:1
本文对空气流过烧结微多孔介质内部对流换热进行了实验研究,分析了不同颗粒直径下对流换热努谢尔特数随流量的变化.结果表明:当颗粒直径为200~40μm时,实验得到的对流换热努谢尔特数与已有研究结果符合很好;当颗粒直径为20μm和10 μm时,实验结果略小于已有研究结果,说明空气在微多孔介质中的对流换热需要考虑微尺度效应的影响.同时,根据实验结果给出了微多孔介质内对流换热努谢尔特数与雷诺数的经验关联式,并提出了考虑努森数的修正关联式. 相似文献
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多孔介质的强制对流换热主要涉及渗流、对流换热、热弥散和热辐射等方面的内容, 文中对这个几个方面的国内外研究进展和发展趋势进行了逐一综述. 同时对主要理论模型、实验研究和经验关联式进行了分类整理, 总结了它们的特点、适用范围和局限性, 并对主要研究成果进行了对比分析, 指出了将来进一步研究的方向和难点所在. 而且通过简化计算得到高温多孔介质冷却过程何时需要考虑辐射换热. 所有这些对多孔介质的理论研究和工程应用都具有指导性的意义.
关键词:
多孔介质
对流换热
渗流
热弥散 相似文献
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In this letter, water base nanofluid flow over wavy surface in a porous medium of spherical packing beds is investigated. The copper oxides particles are taken into account. These properties are rehabilitated when fluid interacts with porous walls. For porous medium, Dupuit–Forchheimer model; an extension of Darcy's law model is utilized. The natures of velocity and temperature profiles of nanofluid are discussed graphically whereas the values of convection heat transfer coefficient in the presence of different nanoparticles concentrations in porous medium is presented in tabular form. The obtained results illustrate that convection heat transfer is improved by nanoparticles concentration but reduces when fluid attract to pores structured medium. On the other hand, when particles are added in fluid, convection heat transfer rate is improved but flow velocity is declined. 相似文献
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A detailed numerical modeling is performed to investigate coupled heat transfer of natural convection, radiation and conduction in high-temperature multilayer thermal insulation (MTI), which consists of high-porous, non-gray semitransparent fibrous materials and reflective foils. Radiation within fibers, radiation between fibers and the reflective foils, conduction within fibers and convection from the fibers to the surrounding fluid are considered. Macroscopic (porous media) modeling is used to determine velocity, pressure and temperatures fields for fibrous insulation with a random packing geometry under natural convection, whereas the radiative transfer equation (RTE) is used to solve the radiative heat flux for non-gray materials. Key features of the macroscopic model include two-dimensional effects, non-gray radiative exchange, and the relaxation of the local thermodynamic non-equilibrium (LTNE). This model was validated by comparison with experimental data and it was used to investigate natural convection of coupled heat transfer in multilayer insulation, numerical results showed that natural convection is more likely to occur when the heated/cooled rate is low, while natural convection can be ignored in simulating steady-state coupled heat transfer in MTI. 相似文献
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This article presents the results of an experimental investigation of heat transfer augmentation by porous media in a natural gas-fired radiant tube burner. The results show that significant heat transfer augmentation is possible with the use of porous ceramic inserts in both premixed and nonpremixed gas-fired radiant tube burners. Furthermore, this work has shown that geometry variations in the porous insert configuration can appreciably alter both heat transfer rates and mixing and chemical reaction rates in these systems. In the case of nonpremixed flames, the effect of variation of insert geometry is more than simple heat transfer augmentation via gas enthalpy conversion to thermal radiation by the porous medium. There is also a significant alteration of the reactive gas mixing (and therefore chemical reaction and heat release) rates along the length of the tube. The basic mechanisms that control the mixing rate and heat release distribution in these systems are still unknown. Nevertheless, it appears reasonable to expect that optimal operating conditions (uniform, maximum heat flux and temperature; and even minimal NOx emissions) can be achieved, at least in the diffusion burner case, solely through porous insert geometric configuration variations. 相似文献
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We report a lattice Boltzmann model that can be used to simulate fluid-solid coupling heat transfer in fractal porous media. A numerical simulation is conducted to investigate the temperature evolution under different ratios of thermal conductivity of solid matrix of porous media to that of fluid. The accordance of our simulation results with the solutions from the conventional CFD method indicates the feasibility and the reliability for the developed lattice Boltzmann model to reveal the phenomena and rules of fluid-solid coupling heat transfer in complex porous structures. 相似文献