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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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《Physica A》2006,362(1):111-117
Although diesel engines have an advantage of low fuel consumption in comparison with gasoline engines, several problems must be solved. One of the major concerns is that diesel exhaust gas has more particle matters (PM) including soot, which are suspected to be linked to human carcinogen. As one of the key technologies, a diesel particulate filter (DPF) has been developed to reduce PM in the after-treatment of exhaust gas. In this study, we conduct lattice Boltzmann (LB) simulation on combustion in porous media. Results show that the combustion reaction is well simulated to observe the decrease of soot attached to the porous wall. This information is indispensable for the better design of DPF, and LB method can be a good tool for combustion simulation in porous media. 相似文献
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The conjugate problem on heat transfer in a system of subsurface channel one-duct heat pipeline-environment is solved by the
finite element method. Thermal regimes of the heat pipeline are analyzed, depending on the temperature at the internal boundary
of the system. Values of the main characteristics of the system are found and adequacy of the proposed model is validated. 相似文献
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The paper summarizes the results of experimental studies of the structuring of the infiltration combustion front in a burning titanium powder layer. The unsteady processes of formation and propagation of cellular and nonuniform combustion waves in heterogeneous media in straight-through and semi-closed channels in conditions of restricted gas exchange and presence of inert gaseous impurities are analyzed. The structural characteristics of cellular combustion waves in a metal powder layer under conditions of natural gas infiltration are reported. 相似文献
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Two-dimensional unsteady gas flows in porous media with heterogeneous-combustion centers are investigated under forced filtration and free convection. With the use of numerical methods, it is shown that complex gas flows including vortex ones can arise under the combustion of solid porous media. In the case of forced filtration, the gas tends to flow around the heated portion of an object preferring to flow along cold regions. Under natural convection, the vortex gas flows, which can exist for a reasonably long time and strongly affect the oxidizer inflow into the reaction zone, arise at the initial moment of the process in the combustion zone and in its vicinities. 相似文献
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Nickolay A. Lutsenko 《Proceedings of the Combustion Institute》2013,34(2):2289-2294
A mathematical model and a numerical method, based on the combination of explicit and implicit finite difference schemes, have been developed for investigating the unsteady gas flows in porous objects with zones of heterogeneous combustion when gas pressure at object boundaries is known. Used approach enables to solve problems of filtration combustion for both forced filtration and free convection, so it can be efficiently applied for modeling the combustion zones in porous media, which may arise from natural or man-caused disasters. One-dimensional unsteady processes of heterogeneous combustion in porous object under free convection have been investigated using numerical experiment. Two regimes of combustion wave propagation have been revealed – wave movement up and down in the object – and it is shown that these regimes are significantly different in degree of burn of solid combustible material, the temperature in the combustion zone and propagation velocity of combustion wave. 相似文献
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This study aims to investigate the time-dependent squeezing of nanofluid flow, comprising carbon nanotubes of dual nature, e.g. single-walled carbon nanotubes, and multi-walled carbon nanotubes,between two parallel disks. Numerical simulations of the proposed novel model are conducted,accompanied by Cattaneo-Christov heat flux in a Darcy-Forchheimer permeable media. Additional impacts of homogeneous–heterogeneous reactions are also noted, including melting heat. A relevant transformation procedure is implemented for the transition of partial differential equations to the ordinary variety. A computer software-based MATLAB function, bvp4c, is implemented to handle the envisioned mathematical model. Sketches portraying impacts on radial velocity, temperature, and concentration of the included parameters are given, and deliberated upon. Skin friction coefficient and local Nusselt number are evaluated via graphical illustrations. It is observed that the local inertia coefficient has an opposite impact on radial velocity and temperature field. It is further perceived that melting and radiation parameters demonstrate a retarding effect on temperature profile. 相似文献
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This paper analyzes well-posedness and stability of a conjugate heat transfer problem in one space dimension. We study a model problem for heat transfer between a fluid and a solid. The energy method is used to derive boundary and interface conditions that make the continuous problem well-posed and the semi-discrete problem stable. The numerical scheme is implemented using 2nd-, 3rd- and 4th-order finite difference operators on Summation-By-Parts (SBP) form. The boundary and interface conditions are implemented weakly. We investigate the spectrum of the spatial discretization to determine which type of coupling that gives attractive convergence properties. The rate of convergence is verified using the method of manufactured solutions. 相似文献
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The thermophysical properties of the nanofluid saturated porous media are used in this work to optimize the thermal design of a spherical electronic device. Quantification of free convective heat transfer has been numerically determined by means of the finite volume method using the SIMPLE algorithm. The Rayleigh number based on the component diameter and water characteristics varies between 6.5x106 and 1.32x109, given the power generated during operation of this active component. The latter is disposed in the center of another sphere maintained isothermal. Its cooling is achieved by means of a porous medium saturated with a water based - Copper nanofluid whose volume fraction varies between 0 (pure water) and 10%. The thermal conductivity of the porous material's matrix ranges from 0 to 40 times that of the base fluid (water). Results of this work show that convective heat transfer systematically increases with this ratio according to a function depending on the Rayleigh number in the whole range of the considered volume fraction. The average Nusselt number also increases with the Rayleigh number according to a conventional power type law while influence of the fraction volume is moderate in the 2-10% range. The results are in agreement with those of previous works for particular thermal conditions. In order to optimize the thermal design of this electronic device, a correlation is proposed, allowing determination of the Nusselt number for any combination of the three influencing parameters for applications in various engineering fields, includind electronics. 相似文献
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Characteristic regimes of premixed gas combustion in high-porosity micro-fibrous porous media 总被引:1,自引:0,他引:1
R. Fursenko S. Minaev K. Maruta H. Nakamura H. Yang 《Combustion Theory and Modelling》2013,17(4):571-581
Dynamical behaviour of the premixed flame propagating in the inert high-porosity micro-fibrous porous media has been studied numerically. Effects of mixture filtration velocity, equivalence ratio and burner transverse size on the flame structure have been investigated and the regions of existence of different combustion regimes have been determined. It was found that the influence of the hydrodynamic instability on the flame dynamics is significant in the case of the moderate and high filtration velocities and this effect is negligible at the low velocities. At the moderate filtration velocities the effect of hydrodynamic instability manifests in the flame front deformation and in particular in the flame inclination. It was found that the flame can be stabilized within the whole interval of the filtration gas velocity, whereas in the ordinary porous media the standing wave is settled only at fixed value of gas filtration velocity. This finding is in line with recent experimental results on combustion in micro-fibrous porous media (Yang et al., Combust. Sci. Tech. 181 (2009), 1–16). Possible physical interpretation of the flame anchoring effect may be given on the base of present numerical analysis. At the high filtration velocities the hydrodynamic instability manifests itself in periodical appearance of the moving wrinkles on the flame front surface which forms non stationary high temperature trailing spots behind the leading part of the flame front. Such dynamics may be associated with splitting wave structures which were revealed in previous experiments (Yang et al., Combust. Sci. Tech. 181 (2009), 1–16). 相似文献
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A. I. Vakser 《Russian Physics Journal》1988,31(9):768-772
Heat transfer processes in one-component (having one type of charged thermal carriers) media with nonlinear surface heat transfer are investigated. It is shown that three-valued (with respect to an externally imposed temperature difference) temperature distributions associated with hysteresis of the thermo-emf are established in the medium for certain conditions on the characteristics of the sample and the surface heat-transfer parameters. The predicted hysteresis effect is analyzed within the framework of the linear model of a thermoelectric medium. Techniques are discussed for the experimental implementation of the given effect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 91–95, September, 1988.The author is indebted to F. G. Bass and Yu. G. Gurevich for a discussion of the results. 相似文献
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Comparison of NMR simulations of porous media derived from analytical and voxelized representations 总被引:3,自引:0,他引:3
Guodong Jin Carlos Torres-Verdín Emmanuel Toumelin 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(2):313-320
We develop and compare two formulations of the random-walk method, grain-based and voxel-based, to simulate the nuclear-magnetic-resonance (NMR) response of fluids contained in various models of porous media. The grain-based approach uses a spherical grain pack as input, where the solid surface is analytically defined without an approximation. In the voxel-based approach, the input is a computer-tomography or computer-generated image of reconstructed porous media. Implementation of the two approaches is largely the same, except for the representation of porous media. For comparison, both approaches are applied to various analytical and digitized models of porous media: isolated spherical pore, simple cubic packing of spheres, and random packings of monodisperse and polydisperse spheres. We find that spin magnetization decays much faster in the digitized models than in their analytical counterparts. The difference in decay rate relates to the overestimation of surface area due to the discretization of the sample; it cannot be eliminated even if the voxel size decreases. However, once considering the effect of surface-area increase in the simulation of surface relaxation, good quantitative agreement is found between the two approaches. Different grain or pore shapes entail different rates of increase of surface area, whereupon we emphasize that the value of the “surface-area-corrected” coefficient may not be universal. Using an example of X-ray-CT image of Fontainebleau rock sample, we show that voxel size has a significant effect on the calculated surface area and, therefore, on the numerically simulated magnetization response. 相似文献
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Koulova Dantchi Traoré Philippe Romat Hubert Wu Jian Louste Christophe 《Journal of Electrostatics》2013,71(3):341-344
In this article the electro-thermo-convective phenomena in a dielectric liquid enclosed in a 2D cavity and subjected to the simultaneous action of an electric field and a thermal gradient is studied. We solved directly the full set of coupled equations of Electro-Hydro-Dynamic (EHD) and energy equation using a finite volume method. In order to characterize the influence of the electric field on heat transfer the liquid is first heated (from a lateral wall) till the thermal steady state is obtained and then the electric potential and injection of electric charge is applied. Two cases of injection are considered: from the lower electrode and from a lateral wall (left or right). The flow pattern and Nusselt number strongly depend on the non-dimensional characteristic parameters: electrical parameter, Rayleigh number, Prandtl number and mobility parameter M. The convective motion passing from a purely thermal convection to a purely electrical convection and the number of electro-thermo-convective rolls patterns are investigated.As a consequence of the analysis of the combined effect of electric and thermal fields on the flow structure and on Nusselt number, we have also evaluated the heat transfer enhancement due to electroconvection. It is shown that the injection of electric charge increases the heat transfer and Nusselt number is independent of Rayleigh number for high enough values of T. 相似文献
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I. V. Mezentsev N. V. Vernikovskaya Yu. I. Aristov V. A. Mukhin 《Thermophysics and Aeromechanics》2006,13(3):403-410
Experimental results on reversing non-stationary heat transfer are presented for filtration of an air flow through an immobile
heat accumulating medium consisting of lead (D = 2.0, 3.5, and 4.5 mm) and glass (D = 3.2 mm) balls. The studied device imitated the cyclic modes of heat regeneration in the ventilation system for domestic
and office rooms. Dependency between the time of flow switching and Re number was measured. The mathematical model describing
heat transfer between a gas flow and an immobile layer of balls was developed. Good correspondence between the experimental
data and calculation results is observed for high Reynolds numbers. For low Re numbers the effect of heat losses is considerable,
and experimental time of flow switching is shorter than the calculation one.
The work was financially supported by the President of the Russian Federation (Grant No. NSh 6526.2006.3), Russian Foundation
for Basic Research (Grant No. 06-08-00982), Foundation “Global energy” and Program “Energy saving of SB RAS”. 相似文献
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D.G. Doornink R.G. Hering 《Journal of Quantitative Spectroscopy & Radiative Transfer》1973,13(4):323-332
Steady-state energy transfer through non-gray radiating and conducting media enclosed by black walls of unequal temperature is studied. A rectangular Milne-Eddington type relation is used to describe the frequency dependence of the absorption coefficient. Temperature distributions and total heat transfer results are presented for materials which absorb radiation (a) of low frequency, (b) of high frequency, (c) within a finite band width, and (d) of all frequencies (gray). The influence of optical thickness (τ0) and conduction to a radiation interaction parameter (N) are examined and the results for non-gray materials are compared with those for a gray analysis. Exact results are compared with those determined by using the optically-thin and the optically-thick approximations, as well as with those evaluated for purely conductive and purely radiative transfer. 相似文献
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Natural convection in an internally heated porous bed of height and diameter of 450 mm and 500 mm, respectively, and superposed with the fluid layer has been experimentally investigated. The onset of natural convection in the bed is indicated by change in the rate of temperature rise within the bed. An empirical model based on local Nusselt number and local Rayleigh number has been developed. A comparison of the present model with the models in literature is made to draw out the differences between the local heat transfer of large multidimensional beds and the average heat transfer of small beds. 相似文献