针对页岩压裂过程中,压裂液返排效率普遍很低的现象,基于高分辨率页岩岩样SEM(scanning electron microscope)电子显微镜扫描图像,利用马尔科夫链蒙特卡罗(Markov Chain Monte Carlo)方法重构得到页岩的三维数字岩心,采用具有高密度比...针对页岩压裂过程中,压裂液返排效率普遍很低的现象,基于高分辨率页岩岩样SEM(scanning electron microscope)电子显微镜扫描图像,利用马尔科夫链蒙特卡罗(Markov Chain Monte Carlo)方法重构得到页岩的三维数字岩心,采用具有高密度比的格子Boltzmann模型,从孔隙尺度来模拟页岩中气水两相驱替过程.首先通过计算表面张力和相对渗透率来验证模型的准确性,然后模拟页岩数字岩心中的油水两相流动,页岩中首先饱和水(气)相,然后从一端注入气(水)相,模拟终止条件为驱替相在出口端发生突破,气水运动黏度比和密度比分别设置为10:1和1:1000.水驱气过程中发生突破时,水相的饱和度为70%,而气驱水过程中发生突破时,气相的饱和度只有4.5%,给出了三维数字岩心中驱替相分布,在气驱水的过程中发生突破时,大部分水被滞留在页岩孔隙中,从而解释了页岩水力压裂中,压裂液返排效率低于10%的现象.展开更多
Pore structure of porous media, including pore size and topology, is rather complex. In immiscible twophase displacement process, the capillary force affected by pore size dominates the two-phase flow in the porous me...Pore structure of porous media, including pore size and topology, is rather complex. In immiscible twophase displacement process, the capillary force affected by pore size dominates the two-phase flow in the porous media, affecting displacement results. Direct observation of the flow patterns in the porous media is difficult, and therefore knowledge about the two-phase displacement flow is insufficient. In this paper, a two-dimensional(2D) pore structure was extracted from a sandstone sample, and the flow process that CO_2 displaces resident brine in the extracted pore structure was simulated using the Navier eStokes equation combined with the conservative level set method. The simulation results reveal that the pore throat is a crucial factor for determining CO_2 displacement process in the porous media. The two-phase meniscuses in each pore throat were in a self-adjusting process. In the displacement process,CO_2 preferentially broke through the maximum pore throat. Before breaking through the maximum pore throat, the pressure of CO_2 continually increased, and the curvature and position of two-phase interfaces in the other pore throats adjusted accordingly. Once the maximum pore throat was broken through by the CO_2, the capillary force in the other pore throats released accordingly; subsequently, the interfaces withdrew under the effect of capillary fore, preparing for breaking through the next pore throat.Therefore, the two-phase displacement in CO_2 injection is accompanied by the breaking through and adjusting of the two-phase interfaces.展开更多
碳捕集、利用与封存技术(carbon capture,utilization and storage,CCUS)是指将CO_(2)从能源利用、工业生产或大气中分离出来,经过提纯运送到可利用或封存场地,以实现被捕集的CO_(2)与大气长期分离的技术。联合国政府间气候变化专门委员...碳捕集、利用与封存技术(carbon capture,utilization and storage,CCUS)是指将CO_(2)从能源利用、工业生产或大气中分离出来,经过提纯运送到可利用或封存场地,以实现被捕集的CO_(2)与大气长期分离的技术。联合国政府间气候变化专门委员会(IPCC)近期在报告中指出:CCUS技术是碳减排与碳中和的“foundation”技术。在我国碳达峰碳中和的“双碳”目标大背景下,CCUS技术被认为是我国实现碳中和目标不可或缺的关键性技术之一。该文对国际、国内主要研究团队和作者研究团队近年来在CO_(2)地质封存、增产致密油/页岩气/深层地热开采过程中的关键热质传递问题研究进行了综述,通过理论分析,利用分子动力学、格子Boltzmann、计算流体力学等模拟方法,和微观孔隙尺度可视化实验、岩心尺度核磁共振实验、超临界压力流体对流换热实验等实验手段,从不同尺度阐述了储层条件下超临界CO_(2)在微纳多孔结构中多相多组分流动与热质传递机理,分析了矿物反应、降压析出、流体变物性、尺度效应等对CO_(2)地质封存和驱油、驱气、采热过程中的影响规律,从而为CO_(2)地质封存和利用的应用提供理论和技术支撑。展开更多
Due to the intricate structure of porous media, the macroscopic petrophysical transport properties such as the permeability and the saturation used for the reservoir prediction also show a very complex nature and are ...Due to the intricate structure of porous media, the macroscopic petrophysical transport properties such as the permeability and the saturation used for the reservoir prediction also show a very complex nature and are difficult to obtain. Thus, a better understanding of the influence of the rock structure on the petrophysical transport properties is important. In this paper, we present a universal finite volume element modeling approach to reconstruct the three dimensional pore models from the micro-CT images based on the commercial software Mimics and ICEM, prior to the pore network model based on some basic assumptions. Moreover, tetra finite volume elements are piled up to realize the geometry reconstruction and the meshing process. Compared with the former methods, this process avoids the tremendously large storage requirement for the reconstructed porous geometry and the failures of meshing these complex polygon geometries, and at the same time improves the predictions of petrophysical transport behaviors. The model is tested on two Berea sandstones, four sandstone samples, two carbonate samples, and one Synthetic Silica. Single- and two phase flow simulations are conducted based on the Navier-Stokes equations in the Fluent software. Good agreements are obtained on both the network structures and predicted single- and two- phase transport properties against benchmark experimental data.展开更多
Porous materials present significant advantages for absorbing radioactive isotopes in nuclear waste streams.To improve absorption efficiency in nuclear waste treatment,a thorough understanding of the diffusion-advecti...Porous materials present significant advantages for absorbing radioactive isotopes in nuclear waste streams.To improve absorption efficiency in nuclear waste treatment,a thorough understanding of the diffusion-advection process within porous structures is essential for material design.In this study,we present advancements in the volumetric lattice Boltzmann method(VLBM)for modeling and simulating pore-scale diffusion-advection of radioactive isotopes within geopolymer porous structures.These structures are created using the phase field method(PFM)to precisely control pore architectures.In our VLBM approach,we introduce a concentration field of an isotope seamlessly coupled with the velocity field and solve it by the time evolution of its particle population function.To address the computational intensity inherent in the coupled lattice Boltzmann equations for velocity and concentration fields,we implement graphics processing unit(GPU)parallelization.Validation of the developed model involves examining the flow and diffusion fields in porous structures.Remarkably,good agreement is observed for both the velocity field from VLBM and multiphysics object-oriented simulation environment(MOOSE),and the concentration field from VLBM and the finite difference method(FDM).Furthermore,we investigate the effects of background flow,species diffusivity,and porosity on the diffusion-advection behavior by varying the background flow velocity,diffusion coefficient,and pore volume fraction,respectively.Notably,all three parameters exert an influence on the diffusion-advection process.Increased background flow and diffusivity markedly accelerate the process due to increased advection intensity and enhanced diffusion capability,respectively.Conversely,increasing the porosity has a less significant effect,causing a slight slowdown of the diffusion-advection process due to the expanded pore volume.This comprehensive parametric study provides valuable insights into the kinetics of isotope uptake in porous structures,facilitating the de展开更多
Brazilian pre-salt reservoirs are renowned for their intricate pore networks and vuggy nature,posing significant challenges in modeling and simulating fluid flow within these carbonate reservoirs.Despite possessing ex...Brazilian pre-salt reservoirs are renowned for their intricate pore networks and vuggy nature,posing significant challenges in modeling and simulating fluid flow within these carbonate reservoirs.Despite possessing excellent petrophysical properties,such as high porosity and permeability,these reservoirs typically exhibit a notably low recovery factor,sometimes falling below 10%.Previous research has indicated that various enhanced oil recovery(EOR)methods,such as water alternating gas(WAG),can substantially augment the recovery factor in pre-salt reservoirs,resulting in improvements of up to 20%.Nevertheless,the fluid flow mechanism within Brazilian carbonate reservoirs,characterized by complex pore geometry,remains unclear.Our study examines the behavior of fluid flow in a similar heterogeneous porous material,utilizing a plug sample obtained from a vugular segment of a Brazilian stromatolite outcrop,known to share analogies with certain pre-salt reservoirs.We conducted single-phase and multi-phase core flooding experiments,complemented by medical-CT scanning,to generate flow streamlines and evaluate the efficiency of water flooding.Subsequently,micro-CT scanning of the core sample was performed,and two cross-sections from horizontal and vertical plates were constructed.These cross-sections were then employed as geometries in a numerical simulator,enabling us to investigate the impact of pore geometry on fluid flow.Analysis of the pore-scale modeling and experimental data unveiled that the presence of dead-end pores and vugs results in a significant portion of the fluid remaining stagnant within these regions.Consequently,the injected fluid exhibits channeling-like behavior,leading to rapid breakthrough and low areal swept efficiency.Additionally,the numerical simulation results demonstrated that,irrespective of the size of the dead-end regions,the pressure variation within the dead-end vugs and pores is negligible.Despite the stromatolite's favorable petrophysical properties,including relatively high porosity 展开更多
Effective thermal conductivity and thermal tortuosity are crucial parameters for evaluating the effectiveness of heat conduction within porous media.The direct pore-scale numerical simulation method is applied to inve...Effective thermal conductivity and thermal tortuosity are crucial parameters for evaluating the effectiveness of heat conduction within porous media.The direct pore-scale numerical simulation method is applied to investigate the heat conduction processes inside porous structures with different morphologies.The thermal conduction performances of idealized porous structures are directly compared with real foams across a wide range of porosity.Real foam structures are reconstructed using X-ray computed tomography and image processing techniques,while Kelvin and Weaire-Phelan structures are generated through periodic unit cell reconstruction.The detailed temperature fields inside the porous structures are determined by solving the heat conduction equation at the pore scale.The results present that the equivalent thermal conductivity of Kelvin and Weaire-Phelan structures is similar to and greater than that of the real foam structure with the same strut porosity.The thermal tortuosity of real foam structure is relatively larger and the heat conduction path becomes straighter by adopting the anisotropic design.The thermal tortuosity of the fluid channels for Kelvin,Weaire-Phelan,and real foam structures is close to one.The thermal conductivity of porous structures with heat transfer fluid increases as the thermal conductivity ratio of fluid to solid becomes larger.A small porosity of porous media leads to a larger equivalent thermal conductivity due to the dominant contribution of porous skeleton in the heat conduction process.Correlations derived from parallel and series models,as well as the Maxwell-Eucken models,provide decent predictions of effective thermal conductivity,with an average error of less than 8%in the entire range of thermal conductivity ratio.展开更多
Porous volumetric solar receivers are one type of solar receivers that can volumetrically absorb solar radiation and achieve efficient solar-to-thermal energy conversion.Porous volumetric solar receivers have been dev...Porous volumetric solar receivers are one type of solar receivers that can volumetrically absorb solar radiation and achieve efficient solar-to-thermal energy conversion.Porous volumetric solar receivers have been developed since 1980s.In this review,we focus on the development progress of the atmospheric and pressurized porous volumetric solar receivers,in which the structural designs,the material selections,the experimental research methods,the comparison of thermal performance,and the transient response characteristic of the receivers were reviewed.On the other hand,the theoretical research methods including the direct pore-scale and volume averaging simulations were introduced.The pore-scale reconstruction method and the procedure to investigate the fluid flow and heat transfer processes at the pore-scale were presented.For the volume averaging method,detailed descriptions for the selection of empirical parameters in the governing equations to be solved were summarized.Typical research results based on these methods were presented and research limitations were also pointed out.Furthermore,the methods for the enhancement of volumetric absorption and the improvement of thermal efficiency of the receivers have been comprehensively reviewed.Two methods including geometrical parameters optimization and spectrally selective absorption were presented in detail.This review will provide a better understanding of the development and research methods for porous volumetric solar receivers,and inspire future studies for the performance improvement of the receivers.展开更多
Direct pore-scale and volume-averaging numerical simulations are two methods for investigating the performance of porous volumetric solar receivers.To clarify the difference in the prediction of heat transfer processe...Direct pore-scale and volume-averaging numerical simulations are two methods for investigating the performance of porous volumetric solar receivers.To clarify the difference in the prediction of heat transfer processes,a direct comparison between these two methods was conducted at both steady state and transient state.The numerical models were established based on X-ray computed tomography scans and a local thermal non-equilibrium model,respectively.The empirical parameters,which are indispensable to the volume-averaging simulation,were determined by Monte Carlo ray tracing and direct pore-scale numerical simulations.The predicted outlet air temperature of the receiver by the volume-averaging simulation method corresponded satisfactorily to that in the direct pore-scale simulation.The largest discrepancies were observed when the receiver's working temperature was elevated,with differences of 5.5%and 3.68%for the steady state and transient state simulations,respectively.However,the volume-averaging method is incapable of capturing the local temperature information of the air and porous skeleton.It underestimates the inlet temperature of the receiver,leading to an overestimation of the receiver's thermal efficiency,with the largest difference being 6.51%.The comparison results show that the volume-averaging model is a good approximation to the pore-scale model when the empirical parameters are carefully selected.展开更多
The lattice Boltzmann method(LBM)is implemented in the Particle Flow Code(PFC)as a pore-scale CFD module and coupled with the particulate discrete element assemblage in PFC using an immersed boundary scheme.The implem...The lattice Boltzmann method(LBM)is implemented in the Particle Flow Code(PFC)as a pore-scale CFD module and coupled with the particulate discrete element assemblage in PFC using an immersed boundary scheme.The implementation of LBM and LBM-PFC coupling is validated with the analytical solutions in a couple of hydrodynamics and fluid-particle interaction problems,i.e.,the accuracy of LBM as a CFD solver is verified by solving channel flow driven by a pressure gradient for which the closed-form solution is also derived;the accuracy of LBM-PFC coupling is validated by solving flow across a cylinder,Taylor-Couette flow,Karman vortex street,and fluid flow through a cylinder array.To demonstrate potential applications of this coupling code,a perforation cavity subjected to axial fluid flush is then tested,showing that the collapse and reconstruction of sand arch in the perforation cavity can be reproduced in this coupling system.The developed system is ready for exploring more complicated physical issues involved in sand production.展开更多
文摘针对页岩压裂过程中,压裂液返排效率普遍很低的现象,基于高分辨率页岩岩样SEM(scanning electron microscope)电子显微镜扫描图像,利用马尔科夫链蒙特卡罗(Markov Chain Monte Carlo)方法重构得到页岩的三维数字岩心,采用具有高密度比的格子Boltzmann模型,从孔隙尺度来模拟页岩中气水两相驱替过程.首先通过计算表面张力和相对渗透率来验证模型的准确性,然后模拟页岩数字岩心中的油水两相流动,页岩中首先饱和水(气)相,然后从一端注入气(水)相,模拟终止条件为驱替相在出口端发生突破,气水运动黏度比和密度比分别设置为10:1和1:1000.水驱气过程中发生突破时,水相的饱和度为70%,而气驱水过程中发生突破时,气相的饱和度只有4.5%,给出了三维数字岩心中驱替相分布,在气驱水的过程中发生突破时,大部分水被滞留在页岩孔隙中,从而解释了页岩水力压裂中,压裂液返排效率低于10%的现象.
基金funded by Key Laboratory of Coal-based CO_2 Capture and Geological Storage,Jiangsu Province,ChinaUS Advanced Coal Technology Consortium(No.2013 DFB60140-08)
文摘Pore structure of porous media, including pore size and topology, is rather complex. In immiscible twophase displacement process, the capillary force affected by pore size dominates the two-phase flow in the porous media, affecting displacement results. Direct observation of the flow patterns in the porous media is difficult, and therefore knowledge about the two-phase displacement flow is insufficient. In this paper, a two-dimensional(2D) pore structure was extracted from a sandstone sample, and the flow process that CO_2 displaces resident brine in the extracted pore structure was simulated using the Navier eStokes equation combined with the conservative level set method. The simulation results reveal that the pore throat is a crucial factor for determining CO_2 displacement process in the porous media. The two-phase meniscuses in each pore throat were in a self-adjusting process. In the displacement process,CO_2 preferentially broke through the maximum pore throat. Before breaking through the maximum pore throat, the pressure of CO_2 continually increased, and the curvature and position of two-phase interfaces in the other pore throats adjusted accordingly. Once the maximum pore throat was broken through by the CO_2, the capillary force in the other pore throats released accordingly; subsequently, the interfaces withdrew under the effect of capillary fore, preparing for breaking through the next pore throat.Therefore, the two-phase displacement in CO_2 injection is accompanied by the breaking through and adjusting of the two-phase interfaces.
文摘碳捕集、利用与封存技术(carbon capture,utilization and storage,CCUS)是指将CO_(2)从能源利用、工业生产或大气中分离出来,经过提纯运送到可利用或封存场地,以实现被捕集的CO_(2)与大气长期分离的技术。联合国政府间气候变化专门委员会(IPCC)近期在报告中指出:CCUS技术是碳减排与碳中和的“foundation”技术。在我国碳达峰碳中和的“双碳”目标大背景下,CCUS技术被认为是我国实现碳中和目标不可或缺的关键性技术之一。该文对国际、国内主要研究团队和作者研究团队近年来在CO_(2)地质封存、增产致密油/页岩气/深层地热开采过程中的关键热质传递问题研究进行了综述,通过理论分析,利用分子动力学、格子Boltzmann、计算流体力学等模拟方法,和微观孔隙尺度可视化实验、岩心尺度核磁共振实验、超临界压力流体对流换热实验等实验手段,从不同尺度阐述了储层条件下超临界CO_(2)在微纳多孔结构中多相多组分流动与热质传递机理,分析了矿物反应、降压析出、流体变物性、尺度效应等对CO_(2)地质封存和驱油、驱气、采热过程中的影响规律,从而为CO_(2)地质封存和利用的应用提供理论和技术支撑。
基金Project supported by the Natural National Science Foundation of China(Grant No.51174170)the National Science and Technology Major Project of China(Grant No.2011ZX05013-006)
文摘Due to the intricate structure of porous media, the macroscopic petrophysical transport properties such as the permeability and the saturation used for the reservoir prediction also show a very complex nature and are difficult to obtain. Thus, a better understanding of the influence of the rock structure on the petrophysical transport properties is important. In this paper, we present a universal finite volume element modeling approach to reconstruct the three dimensional pore models from the micro-CT images based on the commercial software Mimics and ICEM, prior to the pore network model based on some basic assumptions. Moreover, tetra finite volume elements are piled up to realize the geometry reconstruction and the meshing process. Compared with the former methods, this process avoids the tremendously large storage requirement for the reconstructed porous geometry and the failures of meshing these complex polygon geometries, and at the same time improves the predictions of petrophysical transport behaviors. The model is tested on two Berea sandstones, four sandstone samples, two carbonate samples, and one Synthetic Silica. Single- and two phase flow simulations are conducted based on the Navier-Stokes equations in the Fluent software. Good agreements are obtained on both the network structures and predicted single- and two- phase transport properties against benchmark experimental data.
基金supported as part of the Center for Hierarchical Waste Form Materials,an Energy Frontier Research Center funded by the U.S.Department of Energy,Office of Science,Basic Energy Sciences under Award No.DE-SC0016574.
文摘Porous materials present significant advantages for absorbing radioactive isotopes in nuclear waste streams.To improve absorption efficiency in nuclear waste treatment,a thorough understanding of the diffusion-advection process within porous structures is essential for material design.In this study,we present advancements in the volumetric lattice Boltzmann method(VLBM)for modeling and simulating pore-scale diffusion-advection of radioactive isotopes within geopolymer porous structures.These structures are created using the phase field method(PFM)to precisely control pore architectures.In our VLBM approach,we introduce a concentration field of an isotope seamlessly coupled with the velocity field and solve it by the time evolution of its particle population function.To address the computational intensity inherent in the coupled lattice Boltzmann equations for velocity and concentration fields,we implement graphics processing unit(GPU)parallelization.Validation of the developed model involves examining the flow and diffusion fields in porous structures.Remarkably,good agreement is observed for both the velocity field from VLBM and multiphysics object-oriented simulation environment(MOOSE),and the concentration field from VLBM and the finite difference method(FDM).Furthermore,we investigate the effects of background flow,species diffusivity,and porosity on the diffusion-advection behavior by varying the background flow velocity,diffusion coefficient,and pore volume fraction,respectively.Notably,all three parameters exert an influence on the diffusion-advection process.Increased background flow and diffusivity markedly accelerate the process due to increased advection intensity and enhanced diffusion capability,respectively.Conversely,increasing the porosity has a less significant effect,causing a slight slowdown of the diffusion-advection process due to the expanded pore volume.This comprehensive parametric study provides valuable insights into the kinetics of isotope uptake in porous structures,facilitating the de
基金the support of EPIC-Energy Production Innovation Center,hosted by the University of Campinas(UNICAMP)sponsored by FAPESP-Sao Paulo Research Foundation(2017/15736e3 process).
文摘Brazilian pre-salt reservoirs are renowned for their intricate pore networks and vuggy nature,posing significant challenges in modeling and simulating fluid flow within these carbonate reservoirs.Despite possessing excellent petrophysical properties,such as high porosity and permeability,these reservoirs typically exhibit a notably low recovery factor,sometimes falling below 10%.Previous research has indicated that various enhanced oil recovery(EOR)methods,such as water alternating gas(WAG),can substantially augment the recovery factor in pre-salt reservoirs,resulting in improvements of up to 20%.Nevertheless,the fluid flow mechanism within Brazilian carbonate reservoirs,characterized by complex pore geometry,remains unclear.Our study examines the behavior of fluid flow in a similar heterogeneous porous material,utilizing a plug sample obtained from a vugular segment of a Brazilian stromatolite outcrop,known to share analogies with certain pre-salt reservoirs.We conducted single-phase and multi-phase core flooding experiments,complemented by medical-CT scanning,to generate flow streamlines and evaluate the efficiency of water flooding.Subsequently,micro-CT scanning of the core sample was performed,and two cross-sections from horizontal and vertical plates were constructed.These cross-sections were then employed as geometries in a numerical simulator,enabling us to investigate the impact of pore geometry on fluid flow.Analysis of the pore-scale modeling and experimental data unveiled that the presence of dead-end pores and vugs results in a significant portion of the fluid remaining stagnant within these regions.Consequently,the injected fluid exhibits channeling-like behavior,leading to rapid breakthrough and low areal swept efficiency.Additionally,the numerical simulation results demonstrated that,irrespective of the size of the dead-end regions,the pressure variation within the dead-end vugs and pores is negligible.Despite the stromatolite's favorable petrophysical properties,including relatively high porosity
基金supported by the National Natural Science Foundation of China(Grant Nos.52306272 and 52341601)。
文摘Effective thermal conductivity and thermal tortuosity are crucial parameters for evaluating the effectiveness of heat conduction within porous media.The direct pore-scale numerical simulation method is applied to investigate the heat conduction processes inside porous structures with different morphologies.The thermal conduction performances of idealized porous structures are directly compared with real foams across a wide range of porosity.Real foam structures are reconstructed using X-ray computed tomography and image processing techniques,while Kelvin and Weaire-Phelan structures are generated through periodic unit cell reconstruction.The detailed temperature fields inside the porous structures are determined by solving the heat conduction equation at the pore scale.The results present that the equivalent thermal conductivity of Kelvin and Weaire-Phelan structures is similar to and greater than that of the real foam structure with the same strut porosity.The thermal tortuosity of real foam structure is relatively larger and the heat conduction path becomes straighter by adopting the anisotropic design.The thermal tortuosity of the fluid channels for Kelvin,Weaire-Phelan,and real foam structures is close to one.The thermal conductivity of porous structures with heat transfer fluid increases as the thermal conductivity ratio of fluid to solid becomes larger.A small porosity of porous media leads to a larger equivalent thermal conductivity due to the dominant contribution of porous skeleton in the heat conduction process.Correlations derived from parallel and series models,as well as the Maxwell-Eucken models,provide decent predictions of effective thermal conductivity,with an average error of less than 8%in the entire range of thermal conductivity ratio.
基金supported by the National Key Research and Development Program of China(2022YFB3304001)the Key R&D Program of Shaanxi province of China(No.2022GXLH-01-04).
文摘Porous volumetric solar receivers are one type of solar receivers that can volumetrically absorb solar radiation and achieve efficient solar-to-thermal energy conversion.Porous volumetric solar receivers have been developed since 1980s.In this review,we focus on the development progress of the atmospheric and pressurized porous volumetric solar receivers,in which the structural designs,the material selections,the experimental research methods,the comparison of thermal performance,and the transient response characteristic of the receivers were reviewed.On the other hand,the theoretical research methods including the direct pore-scale and volume averaging simulations were introduced.The pore-scale reconstruction method and the procedure to investigate the fluid flow and heat transfer processes at the pore-scale were presented.For the volume averaging method,detailed descriptions for the selection of empirical parameters in the governing equations to be solved were summarized.Typical research results based on these methods were presented and research limitations were also pointed out.Furthermore,the methods for the enhancement of volumetric absorption and the improvement of thermal efficiency of the receivers have been comprehensively reviewed.Two methods including geometrical parameters optimization and spectrally selective absorption were presented in detail.This review will provide a better understanding of the development and research methods for porous volumetric solar receivers,and inspire future studies for the performance improvement of the receivers.
基金supported by the National Natural Science Foundation of China(No.52306272 and No.52293413)the Postdoctoral Research Project Funding in Shaanxi Province(No.2023BSHYDZZ40)。
文摘Direct pore-scale and volume-averaging numerical simulations are two methods for investigating the performance of porous volumetric solar receivers.To clarify the difference in the prediction of heat transfer processes,a direct comparison between these two methods was conducted at both steady state and transient state.The numerical models were established based on X-ray computed tomography scans and a local thermal non-equilibrium model,respectively.The empirical parameters,which are indispensable to the volume-averaging simulation,were determined by Monte Carlo ray tracing and direct pore-scale numerical simulations.The predicted outlet air temperature of the receiver by the volume-averaging simulation method corresponded satisfactorily to that in the direct pore-scale simulation.The largest discrepancies were observed when the receiver's working temperature was elevated,with differences of 5.5%and 3.68%for the steady state and transient state simulations,respectively.However,the volume-averaging method is incapable of capturing the local temperature information of the air and porous skeleton.It underestimates the inlet temperature of the receiver,leading to an overestimation of the receiver's thermal efficiency,with the largest difference being 6.51%.The comparison results show that the volume-averaging model is a good approximation to the pore-scale model when the empirical parameters are carefully selected.
基金The lattice Boltzmann method was implemented in Particle Flow Code when YH was working for Itasca Consulting Group,Inc.
文摘The lattice Boltzmann method(LBM)is implemented in the Particle Flow Code(PFC)as a pore-scale CFD module and coupled with the particulate discrete element assemblage in PFC using an immersed boundary scheme.The implementation of LBM and LBM-PFC coupling is validated with the analytical solutions in a couple of hydrodynamics and fluid-particle interaction problems,i.e.,the accuracy of LBM as a CFD solver is verified by solving channel flow driven by a pressure gradient for which the closed-form solution is also derived;the accuracy of LBM-PFC coupling is validated by solving flow across a cylinder,Taylor-Couette flow,Karman vortex street,and fluid flow through a cylinder array.To demonstrate potential applications of this coupling code,a perforation cavity subjected to axial fluid flush is then tested,showing that the collapse and reconstruction of sand arch in the perforation cavity can be reproduced in this coupling system.The developed system is ready for exploring more complicated physical issues involved in sand production.