Geothermal energy is clean and renewable,derived from the heat stored within accessible depths of the Earth's crust.The adoption of a single-well system for medium-deep and deep geothermal energy extraction has at...Geothermal energy is clean and renewable,derived from the heat stored within accessible depths of the Earth's crust.The adoption of a single-well system for medium-deep and deep geothermal energy extraction has attracted significant interest from the scientific and industrial communities because it effectively circumvents issues such as downhole inter-well connections and induced seismicity.However,the low heat transfer capacity in geothermal formations limits the heat extraction performance of single-well systems and hinders their commercial deployment.This review covers various enhancement concepts for optimizing the heat transfer within single-well systems,emphasizing critical parameters such as heat transfer area,heat transfer coefficient,and temperature difference.Additionally,it presents the thermo-economic evaluation of different configurations of single-well borehole heat exchangers and super-long gravity heat pipes(SLGHPs).The SLHGP,utilizing phase-change heat transfer,is recognized as a highly effective and continuously productive technology,capable of extracting over 1 MW of heat.Its pumpless operation and ease of installation in abandoned wells make it cost-effective,offering a promising economic advantage over traditional geothermal systems.It also highlights the challenges and potential research opportunities that can help identify gaps in research to enhance the performance of single-well geothermal systems.展开更多
Underground non-Darcy fluid flow has been observed and investigated for decades in the petroleum industry. It is deduced by analogy that the fluid flow in enhanced geothermal system (EGS) heat reservoirs may also be i...Underground non-Darcy fluid flow has been observed and investigated for decades in the petroleum industry. It is deduced by analogy that the fluid flow in enhanced geothermal system (EGS) heat reservoirs may also be in the non-Darcy regime under some conditions. In this paper, a transient 3D model was presented, taking into consideration the non-Darcy fluid flow in EGS heat reservoirs, to simulate the EGS long-term heat extraction process. Then, the non-Darcy flow behavior in water- and supercritical CO2 (SCCO2)-based EGSs was simulated and discussed. It is found that non-Darcy effects decrease the mass flow rate of the fluid injected and reduce the heat extraction rate of EGS as a flow resistance in addition to the Darcy resistance which is imposed to the seepage flow in EGS heat reservoirs. Compared with the water-EGS, the SCCO2-EGS are more prone to experiencing much stronger non-Darcy flow due to the much larger mobility of the SCCO2. The non-Darcy flow in SCCO2- EGSs may thus greatly reduce their heat extraction performance. Further, a criterion was analyzed and proposed to judge the onset of the non-Darcy flow in EGS heat reservoirs. The fluid flow rate and the initial thermal state of the reservoir were taken and the characteristic Forchheimer number of an EGS was calculated. If the calculated Forchheimer number is larger than 0.2, the fluid flow in EGS heat reservoirs experiences non-negligible non-Darcy flow characteristic.展开更多
Water transport is of paramount importance to the cold start of proton exchange membrane fuel cells(PEMFCs).Analysis of water transport in cathode catalyst layer(CCL)during cold start reveals the distinct characterist...Water transport is of paramount importance to the cold start of proton exchange membrane fuel cells(PEMFCs).Analysis of water transport in cathode catalyst layer(CCL)during cold start reveals the distinct characteristics from the normal temperature operation.This work studies the effect of CCL mesoscopic pore-morphology on PEMFC cold start.The CCL mesoscale morphology is characterized by two tortuosity factors of the ionomer network and pore structure,respectively.The simulation results demonstrate that the mesoscale morphology of CCL has a significant influence on the performance of PEMFC cold start.It was found that cold-starting of a cell with a CCL of less tortuous mesoscale morphology can succeed,whereas starting up a cell with a CCL of more tortuous mesoscale morphology may fail.The CCL of less tortuous pore structure reduces the water back diffusion resistance from the CCL to proton exchange membrane(PEM),thus enhancing the water storage in PEM,while reducing the tortuosity in ionomer network of CCL is found to enhance the water transport in and the water removal from CCL.For the sake of better cold start performance,novel preparation methods,which can create catalyst layers of larger size primary pores and less tortuous pore structure and ionomer network,are desirable.展开更多
Due to the presence of graphite flake cascades, the real graphite anode of Li-ion battery shows non-iso- tropic characteristic. The present work developed an ellipsoid-based simulated annealing method and numeri- call...Due to the presence of graphite flake cascades, the real graphite anode of Li-ion battery shows non-iso- tropic characteristic. The present work developed an ellipsoid-based simulated annealing method and numeri- cally reconstructed the three-dimensional microstructure of a graphite anode. The reconstructed anode is a composite of three clearly distinguished phases： pore （or electrolyte）, graphite, and solid additives, well representing the non- isotropic heterogeneous characteristic of real graphite anode. Characterization analysis of the reconstructed electrode gives information such as the connectivity of individual phase, the specific interracial area between solid and pore phase, and the pore size distribution. The effects of the ellipsoid size on the structural characteristics of graphite anode were particularly studied. As the size of the ellipsoidal particle slightly increases, the average pore diameter increases and as a result the specific interfacial area between the solid and pore phase in the reconstructed area decreases; compared with the equatorial radius, the polar radius of ellipsoidal graphite particles has more sig- nificant influence on the characteristics of electrode microstructure.展开更多
A mesoscopic pore-scale model of multi-disciplinary processes coupled with electrochemical reactions in lithium-ion batteries is established via a relatively novel numerical method—smoothed particle hydrodynamics(SPH...A mesoscopic pore-scale model of multi-disciplinary processes coupled with electrochemical reactions in lithium-ion batteries is established via a relatively novel numerical method—smoothed particle hydrodynamics(SPH)method.This model is based on mesoscopic treatment to the electrode(including separator)micro-pore structures and solves a group of inter-coupled SPH equations,including charge(ion in electrolyte phase and electron in solid phase),species(Li?in electrolyte phase and lithium in solid active materials),and energy conservation equations.Model parameters,e.g.the physicochemical properties are location-dependent,directly associated with the local component of the medium.The electrochemical reactions are prescribed to occur exactly at the interface of solid active materials and electrolyte.Simulations to isothermal discharge processes of a battery of 2-dimensional idealized micro-pore structure in electrodes and separator preliminarily corroborate the reasonability and capability of the developed SPH model.展开更多
The fracture characteristics of a heat reservoir are of critical importance to enhanced geothennal systems,which can be investigated by theoretical modeling.This paper presents the development of a novel flow.Fesistor...The fracture characteristics of a heat reservoir are of critical importance to enhanced geothennal systems,which can be investigated by theoretical modeling.This paper presents the development of a novel flow.Fesistor network model to describe the hydraulic processes in heat reservoirs.The fractures in the reservoir are simplified by using flow resistors and the typically complicated fracture network of the heat reservoir is converted into a flowresistor network with a reasonably simple pattern.For heat reservoirs with various fracture configurations,the corresponding flow-resistor networks are identical in terms of framework though the networks may have difftrent section numbers and the flow resistors may have different values.In this paper,numerous cases of different section numbers and resistor values are calculated and the results indicate that the total number of flow resistances between the injection and production wells is primarily determined by the number of fractures in the reservoir.It is also observed that a linear dependence of the total flow resistance on the number of fractures and the relation is obtained by the best fit of the calculation results.Besides,it perfbmis a case study dealing with the Soultz enhanced geothermal system(EGS).In addition,the fracture numbers underneath specific well systems are derived.The results provide in sight on the tortuosity of the flow path betwee n different wells.展开更多
基金supported by the National Key Research andDevelopmentProgramofChina(GrantNos.2021YFB1507300 and 2021YFB1507302)the National Natural Science Foundation of China(Grant Nos.52206126 and 52206287)+1 种基金the Jiangyin Science and Technology Innovation Special Fund,China(Grant No.JY0604A021015210001PB)the Jiangsu Provincial Carbon Peak Carbon Neutralization Technology Innovation Special Fund,China(Grant No.BE2022012).
文摘Geothermal energy is clean and renewable,derived from the heat stored within accessible depths of the Earth's crust.The adoption of a single-well system for medium-deep and deep geothermal energy extraction has attracted significant interest from the scientific and industrial communities because it effectively circumvents issues such as downhole inter-well connections and induced seismicity.However,the low heat transfer capacity in geothermal formations limits the heat extraction performance of single-well systems and hinders their commercial deployment.This review covers various enhancement concepts for optimizing the heat transfer within single-well systems,emphasizing critical parameters such as heat transfer area,heat transfer coefficient,and temperature difference.Additionally,it presents the thermo-economic evaluation of different configurations of single-well borehole heat exchangers and super-long gravity heat pipes(SLGHPs).The SLHGP,utilizing phase-change heat transfer,is recognized as a highly effective and continuously productive technology,capable of extracting over 1 MW of heat.Its pumpless operation and ease of installation in abandoned wells make it cost-effective,offering a promising economic advantage over traditional geothermal systems.It also highlights the challenges and potential research opportunities that can help identify gaps in research to enhance the performance of single-well geothermal systems.
基金This work was supported by the National Key R&D Program of China (2018YFB1501804)the Strategic Priority Research Program of Chinese Academy of Sciences (XDA21060700)+1 种基金the National Natural Science Foundation of China (Grant No. 41702256)the Natural Science Foundation of Guangdong Province (2017A030310328).
文摘Underground non-Darcy fluid flow has been observed and investigated for decades in the petroleum industry. It is deduced by analogy that the fluid flow in enhanced geothermal system (EGS) heat reservoirs may also be in the non-Darcy regime under some conditions. In this paper, a transient 3D model was presented, taking into consideration the non-Darcy fluid flow in EGS heat reservoirs, to simulate the EGS long-term heat extraction process. Then, the non-Darcy flow behavior in water- and supercritical CO2 (SCCO2)-based EGSs was simulated and discussed. It is found that non-Darcy effects decrease the mass flow rate of the fluid injected and reduce the heat extraction rate of EGS as a flow resistance in addition to the Darcy resistance which is imposed to the seepage flow in EGS heat reservoirs. Compared with the water-EGS, the SCCO2-EGS are more prone to experiencing much stronger non-Darcy flow due to the much larger mobility of the SCCO2. The non-Darcy flow in SCCO2- EGSs may thus greatly reduce their heat extraction performance. Further, a criterion was analyzed and proposed to judge the onset of the non-Darcy flow in EGS heat reservoirs. The fluid flow rate and the initial thermal state of the reservoir were taken and the characteristic Forchheimer number of an EGS was calculated. If the calculated Forchheimer number is larger than 0.2, the fluid flow in EGS heat reservoirs experiences non-negligible non-Darcy flow characteristic.
文摘Water transport is of paramount importance to the cold start of proton exchange membrane fuel cells(PEMFCs).Analysis of water transport in cathode catalyst layer(CCL)during cold start reveals the distinct characteristics from the normal temperature operation.This work studies the effect of CCL mesoscopic pore-morphology on PEMFC cold start.The CCL mesoscale morphology is characterized by two tortuosity factors of the ionomer network and pore structure,respectively.The simulation results demonstrate that the mesoscale morphology of CCL has a significant influence on the performance of PEMFC cold start.It was found that cold-starting of a cell with a CCL of less tortuous mesoscale morphology can succeed,whereas starting up a cell with a CCL of more tortuous mesoscale morphology may fail.The CCL of less tortuous pore structure reduces the water back diffusion resistance from the CCL to proton exchange membrane(PEM),thus enhancing the water storage in PEM,while reducing the tortuosity in ionomer network of CCL is found to enhance the water transport in and the water removal from CCL.For the sake of better cold start performance,novel preparation methods,which can create catalyst layers of larger size primary pores and less tortuous pore structure and ionomer network,are desirable.
基金supported by the Key Scientific Development Project of Guangdong Province(2015A030308019)the Guangzhou Scientific and Technological Development Plan(2014J4100217)the Hundred Talents Program of Chinese Academy of Sciences
文摘Due to the presence of graphite flake cascades, the real graphite anode of Li-ion battery shows non-iso- tropic characteristic. The present work developed an ellipsoid-based simulated annealing method and numeri- cally reconstructed the three-dimensional microstructure of a graphite anode. The reconstructed anode is a composite of three clearly distinguished phases： pore （or electrolyte）, graphite, and solid additives, well representing the non- isotropic heterogeneous characteristic of real graphite anode. Characterization analysis of the reconstructed electrode gives information such as the connectivity of individual phase, the specific interracial area between solid and pore phase, and the pore size distribution. The effects of the ellipsoid size on the structural characteristics of graphite anode were particularly studied. As the size of the ellipsoidal particle slightly increases, the average pore diameter increases and as a result the specific interfacial area between the solid and pore phase in the reconstructed area decreases; compared with the equatorial radius, the polar radius of ellipsoidal graphite particles has more sig- nificant influence on the characteristics of electrode microstructure.
基金supported by the National Natural Science Foundation of China (51206171)the Director Innovation Foundation of Guangzhou Institute of Energy Conversion (y207r31001)+1 种基金the Amperex Technology Limited (ATL-Dongguan)the CAS ‘‘100 talents’’ Plan (FJ)
文摘A mesoscopic pore-scale model of multi-disciplinary processes coupled with electrochemical reactions in lithium-ion batteries is established via a relatively novel numerical method—smoothed particle hydrodynamics(SPH)method.This model is based on mesoscopic treatment to the electrode(including separator)micro-pore structures and solves a group of inter-coupled SPH equations,including charge(ion in electrolyte phase and electron in solid phase),species(Li?in electrolyte phase and lithium in solid active materials),and energy conservation equations.Model parameters,e.g.the physicochemical properties are location-dependent,directly associated with the local component of the medium.The electrochemical reactions are prescribed to occur exactly at the interface of solid active materials and electrolyte.Simulations to isothermal discharge processes of a battery of 2-dimensional idealized micro-pore structure in electrodes and separator preliminarily corroborate the reasonability and capability of the developed SPH model.
文摘The fracture characteristics of a heat reservoir are of critical importance to enhanced geothennal systems,which can be investigated by theoretical modeling.This paper presents the development of a novel flow.Fesistor network model to describe the hydraulic processes in heat reservoirs.The fractures in the reservoir are simplified by using flow resistors and the typically complicated fracture network of the heat reservoir is converted into a flowresistor network with a reasonably simple pattern.For heat reservoirs with various fracture configurations,the corresponding flow-resistor networks are identical in terms of framework though the networks may have difftrent section numbers and the flow resistors may have different values.In this paper,numerous cases of different section numbers and resistor values are calculated and the results indicate that the total number of flow resistances between the injection and production wells is primarily determined by the number of fractures in the reservoir.It is also observed that a linear dependence of the total flow resistance on the number of fractures and the relation is obtained by the best fit of the calculation results.Besides,it perfbmis a case study dealing with the Soultz enhanced geothermal system(EGS).In addition,the fracture numbers underneath specific well systems are derived.The results provide in sight on the tortuosity of the flow path betwee n different wells.
