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A Multiple-Relaxation-Time Lattice Boltzmann Model for Natural Convection in a Hydrodynamically and thermally Anisotropic Porous Medium under local thermal non-equilibrium Conditions

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Journal of thermal Science 2020年第3期29卷 609-622页

作者： YANG Bo WU Wei LI Maodong ZHAI Wei Guangzhou Special Pressure Equipment Inspection and Research Institute Guangzhou 510663China School of Chemistry and Chemical Engineering South China University of TechnologyGuangzhou 510640China

To investigate the natural convective process in a hydrodynamically and thermally anisotropic porous medium at the representative elementary volume(REV)scale,the present work presented a multiplerelaxation-time lattice Boltzmann method(MRT-LBM)based on the assumption of local thermal non-equilibrium conditions(LTNE).Three sets of distribution function were used to solve the coupled momentum and heat transfer *** set was used to compute the flow field based on the generalized non-Darcy model;the other two sets were used to solve the temperature fields of fluid and solid under the *** describe the anisotropy of flow field of the porous media,a permeability tensor and a Forchheimer coefficient tensor were introduced into the ***,a heat conductivity tensor and a special relaxation matrix with some off-diagonal elements were selected for the thermal ***,by selecting an appropriate equilibrium moments and discrete source terms accounting for the local thermal non-equilibrium effect,as well as choosing an off-diagonal relaxation matrix with some specific elements,the presented model can recover the exact governing equations for natural convection under LTNE with anisotropic permeability and thermal conductivity with no deviation terms through the Chapman-Enskog ***,the proposed model was adopted to simulate several benchmark *** agreements with results in the available literatures can be achieved,which indicate the wide practicability and the good accuracy of the present model.

关键词： lattice Boltzmann method natural convection in anisotropic porous medium local thermal non-equilibrium

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Experimental and numerical analysis of the hydraulic and thermal performances of the gradually-varied porous volumetric solar receiver

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Science China(Technological Sciences) 2020年第7期63卷 1224-1234页

作者： DU Shen LI ZengYao HE YaLing LI Dong XIE XiangQian GAO Yang Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education School of Energy and Power EngineeringXi'an Jiaotong UniversityXi'an 710049China Science and Technology on Space Physics Laboratory China Academy of Launch Vehicle TechnologyBeijing 100076China

A gradually-varied porous structure is designed to increase the thermal performance of the porous volumetric solar *** on the replica method and multilayer recoating technique, the silicon carbide porous ceramic with linear-changed geometrical parameters is fabricated. The performances of the uniform and gradually-varied porous volumetric solar receivers are studied by both experiment and numerical simulation. An optimization method combining genetic algorithm and computational fluid dynamics analysis is applied to determine the optimum porosity distribution. The results present that porous volumetric solar receiver with linear-changed geometrical parameters exhibits better thermal performance than the uniform porous volumetric solar receivers, especially when the thickness of the receiver is small. Larger porosity in the front is beneficial for increasing the solar radiation penetration depth, which limits the reflectance and thermal radiative losses. Smaller porosity in the rear traps more solar radiation and increases the convective heat transfer. When the receiver’s thickness is larger, the performance of the gradually-varied volumetric solar receiver is nearly identical to that of the uniform receiver with largest porosity. The double-layer configuration is found to be the optimized structure of the gradually-varied porous volumetric solar receiver. The thermal efficiency could be further improved using genetic algorithm with an 11 K increase of the outlet temperature.

关键词： gradually-varied porous volumetric solar receiver replica method local thermal non-equilibrium heat transfer analysis optimization design

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Effect of asymmetrical wall heat flux and wall temperature ratio on mixed convection in a vertical micro-porous-channel with internal heat generation

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Propulsion and Power Research 2020年第4期9卷 394-407页

作者： V.Leela K.N.Seetharamu Nagabhushanam Kotloni R.Gangadhara Reddy PES University Bengaluru.Karnataka560085India RV Institute of Technology and Management.Bengaluru.Karnataka 560076India AMC Engineering College BengaluruKarnataka560083India

Mixed convective heat transfer in a vertical parallel plate micro-porous channel with internal heat generation and viscous dissipation,varying wall heat flux ratio and wall temperature ratio at the boundaries is investigated using the Darcy-Brinkman model under local thermal non-equilibrium *** solution for both fluid and solid temperature distributions are obtained by applying the finite element *** effect of pertinent parameters such as Brinkman number,Rayleigh number,Darcy number,inter-phase heat transfer coefficient,porosity scaled thermal conductivity ratio and solid internal heat generation are *** results indicate that the Nusselt number increases with the increase in the solid internal heat generation as well as Rayleigh number in both wall heat flux ratio and wall temperature ratio boundary *** is observed that with the quantitative increase in viscous dissipation parameter Br,Nusselt number Nu increases in the presence of internal heat generation and it decreases in the absence of internal heat generation,for a specific range of values of wall heat flux ratio and wall temperature *** this range Nu increases with the increase in Dr regardless of internal heat *** the cases,constant wall temperature and wall heat flux ratios,good correlation is observed in the results obtained with that of available in the literature.

关键词： Wallheat flux ratio Wallt emperatureratio Internal heat generation Mixed convection Viscous dissipation local thermal non-equilibrium

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Analyzing Heat Extraction and Sustainability of EGS with a Novel Model

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Journal of Earth Science and Engineering 2013年第10期3卷 690-700页

作者： Jiliang Chen Liang Luo Fangming Jiang Laboratory of Advanced Energy Systems CAS Key Laboratory of Renewable Energy Guangzhou Institute of Energy ConversionCAS (Chinese Academy of Sciences) Guangzhou 510640 China

We investigate the subsurface heat exchange process in EGS （enhanced geothermal systems） with a previously developed novel model. This model treats the porous heat reservoir as an equivalent porous medium of a single porosity. However, it considers local thermal non-equilibrium between solid rock matrix and fluid flowing in the factures and employs two energy conservation equations to describe heat transfer in the rock matrix and in the fractures, respectively, enabling the modeling and analyses of convective heat exchange in the heat reservoir. Another salient feature of this model is its capability of simulating the complete subsurface heat exchange process in EGS. The EGS subsurface geometry of interest physically consists of multiple domains： open channels for injection and production wells, the artificial heat reservoir, and the rocks enclosing the heat reservoir, while computationally we treat it as a single-domain of multiple sub-regions associated with different sets of characteristic properties （porosity and permeability, etc.）. This circumvents typical difficulties about matching boundary conditions between sub-domains in traditional multi-domain approaches and facilitates numerical implementation and simulation of the complete subsurface heat exchange process. This model is used to perform a comprehensive parametric study with respect to an imaginary doublet EGS. Effects of several parameters, including the permeability of heat reservoir, heat exchange coefficient in the heat reservoir, the specific area of fractures in the heat reservoir, and thermal compensation from surrounding rocks, on the heat extraction efficiency and EGS lifetime are analyzed.

关键词： Hot dry rock technology enhanced or engineered geothermal system local thermal non-equilibrium numerical model porous heat reservoir.

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