A novel single-well geothermal system for hot dry rock geothermal energy exploitation

Existing hot dry rock geothermal projects are commonly confronted with some technical issues, such as corrosion and scaling, and water loss. To resolve these issues, the present work proposes a novel system for mining hot dry rock geothermal energy, in which a reservoir is combined with a heat pipe system. The new system encompasses a heat pipe placed in a single-well to extract hot dry rock geothermal energy, while an artificial reservoir is built around the main endothermic region of the well, which is permeable and saturated with carbon dioxide (CO2). This wellbore structure design may stimulate a stronger natural convection in the reservoir, resulting in a higher thermal power production. To evaluate the proposed system, an extensive numerical investigation was conducted. The comparison of the proposed system with the conventional downhole heat exchanger (DHE) system in terms of heat extraction performance indicates clear superiority of the proposed system primarily due to the associated thermosyphon effect of CO2 fluid in the reservoir. To better understand how operating and design variables affect the heat extraction performance of the system, a detailed sensitivity analysis was conducted taking into consideration a wide range of possible configurations and working conditions. The eventually obtained knowledge will guide the design of the system in practice. (C) 2018 Elsevier Ltd. All rights reserved

Numerical study on variable thermophysical properties of heat transfer fluid affecting EGS heat extraction

Thermophysical properties of heat transfer fluid may experience significant changes during heat extraction process in enhanced geothermal system (EGS). The present work extends a previous EGS model by implementing pressure- and temperature-dependent thermophysical properties of real water and supercritical carbon dioxide (SCCO2), and employed the new model to simulate the long-term heat extraction processes of water-EGS and SCCO2-EGS. Comparison between the model results finds at a given fluid injection pressure, the lifetime of water-EGS is longer than that of SCCO2-EGS while the heat extraction rate of the latter is higher than the former, leading to approximately the same cumulative heat extraction amount at the end of EGS operation. Relative to water, larger density-temperature dependence of SCCO2 leads to stronger natural convection of fluid flow in EGS reservoir and makes the heat extraction process of SCCO2-EGS more prefers to perform in the reservoir bottom region. The natural convection flow in the reservoir of SCCO2-EGS is found to be relatively stronger if the reservoir permeability is smaller, the fluid injection pressure is lower, or the reservoir is of a larger volume. Simulations with respect to two groups of cases, one of which consists of water-based heat transfer fluids and the other SCCO2-based fluids, comprehensively reveal variable thermophysical property effects on EGS heat extraction. The production performance of SCCO2-EGS is generally more sensitive to the variation of fluid thermophysical properties; for both water- and SCCO2-EGS, the net electric power output is positively related with the density and specific heat capacity of fluid, and negatively related with the viscosity of fluid, whereas the thermal conductivity of fluid has little effect on the net electric power output. (C) 2015 Elsevier Ltd. All rights reserved

anovelflowresistornetworkmodelforcharacterizingenhancedgeothermalsystemheatreservoir

The fracture characteristics of a heat reservoir are of critical importance to enhanced geothermal systems, which can be investigated by theoretical modeling. This paper presents the development of a novel flow-resistor 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 different 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 performs 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 insight on the tortuosity of the flow path between different wells

Thermal behavior study of discharging/charging cylindrical lithium-ion battery module cooled by channeled liquid flow

With respect to channeled liquid cooling thermal management system of electric vehicle battery pack, a thermal model is established for a battery module consisting of 71 18650-type lithium-ion batteries. In this model, thermal-lumped treatment is implemented for each single battery in the module and heat generation of a single battery is determined based on experimental measurements. In particular, heat conduction between neighboring batteries and heat transfer from the battery to the fluid channel outer wall are carefully modeled. We study, by the developed model, the battery module's thermal behavior, and investigate the effects of discharge/charge C-rate, the liquid flow rate, the heat exchange area between neighboring batteries, and the interfacing area of the battery and the channel outer wall. The simulation results corroborate the effectiveness of the cooling system. It is found from simulation results that: (1) increasing the discharge/charge C-rate leads to higher temperature and worsens the temperature uniformity in the battery module; (2) increasing the liquid flow rate can significantly lower the temperature and improves the temperature uniformity in the battery module; (3) increasing the heat exchange area between neighboring batteries slightly improves the temperature uniformity in the battery module, but only has negligible effect on lowering the temperature of the module; (4) increasing the interfacing area of the battery and the channel outer wall can significantly lower the maximum temperature in the battery module but worsens the temperature uniformity in the module. (C) 2017 Elsevier Ltd. All rights reserved

A novel flow-resistor network model for characterizing enhanced geothermal system heat reservoir

The fracture characteristics of a heat reservoir are of critical importance to enhanced geothermal systems, which can be investigated by theoretical modeling. This paper presents the development of a novel flow-resistor 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 flow-resistor 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 different 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 performs 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 insight on the tortuosity of the flow path between different wells

A novel entropy-based fault diagnosis and inconsistency evaluation approach for lithium-ion battery energy storage systems

Detection and diagnosis of faults at the early stage, as well as inconsistency monitoring and control are of extreme importance for operating Li-ion batteries (LIBs) safely and reliably, handling performance degradation and cell unbalancing, and avoiding accidents like thermal runaway (TR). In this work, a general procedure based on multi-level Shannon entropy algorithms is put forward to perform fault diagnosis as well as inconsistency evaluation for LIB-based energy storage systems (ESSs). More specifically, the cell-level Shannon entropy algorithm is used to detect faults by comparing Shannon entropies of different LIB cells in each module while the module-level and cluster-level Shannon entropy algorithms are used to evaluate the overall inconsistency among LIB cells in each module and in each cluster respectively. The proposed approach is then applied in a large-scale LIB-based ESS (1 MW/2 MWh). Through simulated data, the availability of the cell-level Shannon entropy algorithm to detect small changes in gradual faults is testified while the module-level and the cluster-level Shannon entropy algorithms are demonstrated to be effective for assessing inconsistences of LIBs in every module and in every cluster respectively, by comparing results of the normal case with those from two cases each with a different faulty LIB cell at the early stage of internal short circuit (ISC)

A numerical study of non-Darcy flow in EGS heat reservoirs during heat extraction

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

Analysis of lithium-ion battery thermal models inaccuracy caused by physical properties uncertainty

Thermal management is of upmost importance for the safe and efficient operation of lithium-ion batteries in electric vehicles. To this purpose it is required to develop reliable thermal models to assess the behavior of the battery under different operating and ambient conditions. In this work, it is proposed a three-dimensional thermal model of the 40Ah LiFePO4/graphite prismatic battery, which is a particular type of the lithium-ion battery (LIB), and it is analyzed the uncertainty related to the base data needed to run the model. The base data comprises, among others, the battery material physical properties and their dependence on the temperature, and the special "double-coated electrodes" structure. The charge and discharge processes of the 40Ah LiFePO4/ graphite prismatic battery are tested experimentally to verify the reliability of the thermal model. The deviation of the thermal model predictions caused by the uncertainty of the physical parameters of the battery is fully investigated numerically. The influence of physical parameters on the predictions is verified for the battery surface temperature and temperature difference between the battery interior and the surface. For the range of the properties tested the highest deviations of the predicted surface temperature and the inside and surface temperature difference are 0.14 degrees C and 0.93 degrees C during discharge at room temperature, respectively. Based on this investigation, it is proposed a simplified one-dimensional thermal model, which has the potential of being an expedite way of calculating the temperature distribution inside most commercial prismatic batteries. The comparison of the temperature distribution predictions using the three-dimensional thermal model and the simplified model indicates that the temperature gradient predictions obtained with the two models are in close agreement; the maximum relative difference of the two models is only 0.5%. The simplified thermal model, in what concerns the uncertainty of the physical properties, may provide an easy-to-use preliminary tool to evaluate the temperature distribution related to prismatic batteries

Experimental investigation of the laminar flow and heat transfer performance of a harmonica tube with or without mini-fins

Thermal and flow performance was evaluated experimentally for different geometric shapes of a harmonica tube with or without mini-fins heat sink. Four different arrangements for the harmonica tube with smooth channels and channels with mini-fins were investigated under laminar forced convection with water as the cooling fluid. The pressure drop, friction factor and volumetric heat transfer coefficient were determined for Reynolds number ranging from 250 to 2300, and the four harmonica tube arrangements were compared. The results show that the transition from the laminar to turbulent flow regimes shifts to a smaller Reynolds number due to the presence of the mini-fins as compared to the smooth channels. An increase of the inlet fluid temperature leads to a reduction of the heat transfer performance and also flow resistance. Due mainly to the augmented heat transfer surface, the performance evaluation criterion value of the harmonica tube with mini-fins is always higher than 1 in the researched Reynolds number range and it can be as high as about 1.7 when the fluid flow is in the laminar to turbulent transition regime. Moreover, it is found that lowering the height of mini-channels, or for a given mini-channel geometry, increasing the number of mini-channels can improve the overall heat transfer performance of the harmonica tube with mini-fins

LHP heat transfer performance: A comparison study about sintered copper powder wick and copper mesh wick

Heat transfer performance of loop heat pipe (LHP) is tightly related with the wick positioned between its evaporator and compensation chamber. Experiments were carried out to investigate the effects of wick on LHP heat transfer performance. Two wicks, a sintered copper powder wick and a copper mesh wick, were considered for comparison. The former has larger porosity; its pore size spans within a wide range, but smaller than that of the latter. The measured temperature data indicate that the sintered wick LHP starts up faster and operates more stably. The overall thermal resistance of the sintered wick LHP is also slightly lower than that of the mesh wick LHP. Moreover, the sintered wick LHP is found to be able to start up with heat load as low as 5 Watts. (C) 2015 Elsevier Ltd. All rights reserved