A kind of direct numerical simulation method suitable for supercritical carbon dioxide jet flow has been discussed in this paper. The form of dimensionless nonconservative compressible Navier-Stokes equations in a two...A kind of direct numerical simulation method suitable for supercritical carbon dioxide jet flow has been discussed in this paper. The form of dimensionless nonconservative compressible Navier-Stokes equations in a two-dimensional cartesian coordinate system is derived in detail. High accurate finite difference compact schemes based on non-uniform grid system are introduced to solve the equations. The simulation results of the three vortex pairing phenomenon of plane mixing layer and a compressible axisymmetric jet flow field show that the discussed numerical simulation method is feasible to calculate the supercritical carbon dioxide jet fluid. And it is found that the difficulties of splitting the convective terms in conservation Navier-Stokes equations, which are brought by the supercritical carbon dioxide fluid pressure state equation, can be avoided by solving the nonconservative compressible Navier-Stokes equations.展开更多
This paper aims at using of an approach integrating the fuzzy logic strategy for hypoxemic hypoxia tissue blood carbon dioxide human optimal control problem. To test the efficiency of this strategy, the authors propos...This paper aims at using of an approach integrating the fuzzy logic strategy for hypoxemic hypoxia tissue blood carbon dioxide human optimal control problem. To test the efficiency of this strategy, the authors propose a numerical comparison with the direct method by taking the values of determinant parameters of cardiovascular-respiratory system for a 30 years old woman in jogging as her regular physical activity. The results are in good agreement with experimental data.展开更多
The supercritical carbon dioxide （SC-CO2） jet can break rocks at higher penetration rates and lower threshold pressures than the water jet. The abrasive SC-CO2 jet, formed by adding solid particles into the SC-CO2 j...The supercritical carbon dioxide （SC-CO2） jet can break rocks at higher penetration rates and lower threshold pressures than the water jet. The abrasive SC-CO2 jet, formed by adding solid particles into the SC-CO2 jet, is expected to achieve higher operation efficiency in eroding hard rocks and cutting metals. With the computational fluid dynamics numerical simulation method, the characteristics of the flow field of the abrasive SC-CO2 jet are analyzed, as well as the main influencing factors. Results show that the two-phase axial velocities of the abrasive SC-CO2 jet is much higher than those of the abrasive water jet, when the pressure difference across the jet nozzle is held constant at 20 MPa, the optimal standoff distance for the largest particle impact velocity is approximately 5 times of the jet nozzle diameter; the fluid temperature and the volume concentration of the abrasive particles have modest influences on the two-phase velocities, the ambient pressure has a negligible influence when the pressure difference is held constant. Therefore the abrasive SC-CO2 jet is expected to assure more effective erosion and cutting performance. This work can provide guidance for subsequent lab experiments and promote practical applications.展开更多
The pure supercritical carbon dioxide（SC-CO2） fracturing prevents the clay from swelling and avoids the water lock as compared with the slick-water fracturing. The CO2 molecule could replace the CH4 adsorbed in orga...The pure supercritical carbon dioxide（SC-CO2） fracturing prevents the clay from swelling and avoids the water lock as compared with the slick-water fracturing. The CO2 molecule could replace the CH4 adsorbed in organic matter and tiny particles on the clay mineral surface in the formation. This leads to an increased cumulative gas production rate. The SC-CO2 fracturing is an alternative waterless fracturing technique for an effective future development of shale gas reservoirs. Due to its low density and viscosity as compared with the slick-water, it attracts attentions for the proppant transport. In this paper, the two phase flow of the SC-CO2 and the proppant in fractures during the SC-CO2 fracturing is analyzed with the computational fluid dynamics method. The characteristics of the proppant transport by the SC-CO2 fracturing and the slick-water fracturing are compared. Moreover, a sensitivity analysis is also performed to see the influence of various parameters on the proppant transport ability of the SC-CO2 fracturing. It is shown that the proppants in the SC-CO2 and the slick-water have similar distribution characteristics. Reducing the proppant density, the proppant diameter, and the solid volume fraction as well as increasing the injection rate can all have similar filling effects on the fractures. The feasibility of the proppant transport by the SC-CO2 fracturing in fractures is revealed and a guidance is provided for the SC-CO2 fracturing design.展开更多
Molten salt and supercritical carbon dioxide(S-CO_(2))are important high temperature heat transfer media,but molten salt/S-CO_(2) heat exchanger has been seldom reported.In present paper,heat transfer in printed circu...Molten salt and supercritical carbon dioxide(S-CO_(2))are important high temperature heat transfer media,but molten salt/S-CO_(2) heat exchanger has been seldom reported.In present paper,heat transfer in printed circuit heat exchanger(PCHE)with molten salt and S-CO_(2) is simulated and analyzed.Since S-CO_(2) can be drove along passage wall by strong buoyancy force with large density difference,its heat transfer is enhanced by natural convection.In inlet region,natural convection weakens along flow direction with decreasing Richardson number,and the thermal boundary layer becomes thicker,so local heat transfer coefficient of S-CO_(2) significantly decreases.In outlet region,turbulent kinetic energy gradually increases,and then heat transfer coefficient increases for turbulent heat transfer enhancement.Compared with transcritical CO_(2) with lower inlet temperature,local heat transfer coefficient of S-CO_(2) near inlet is lower for smaller Richardson number,while it will be higher for larger turbulent kinetic energy near outlet.Performance of PCHE is mainly determined by the pressure drop in molten salt passage and the heat transfer resistance in S-CO_(2) passage.When molten salt passage width increases,molten salt pressure drop significantly decreases,and overall heat transfer coefficient slightly changes,so the comprehensive performance of PCHE is improved.As a result,PCHE unit with three semicircular passages and one semi-elliptic passage has better performance.展开更多
The low power consumption of the near-critical compressor is the key factor for the high efficiency of supercritical CO_(2)Brayton cycle.In the numerical simulation of the compressor,the rapid changes in the thermophy...The low power consumption of the near-critical compressor is the key factor for the high efficiency of supercritical CO_(2)Brayton cycle.In the numerical simulation of the compressor,the rapid changes in the thermophysical properties of the CO_(2)near the critical point make it difficult to capture the condensation phenomenon.This paper investigates the influence of fluid physical properties on the condensation phenomenon.Firstly,the differences in the physical properties of CO_(2)in the SRK EOS(equation of state),PR EOS,and SW EOS are compared.Then,the simulation of nozzles and compressors were carried out and discussed.Results show that the condensation positions predicted by the three EOSs are basically the same.Compared with SW EOS,the disparities between the maximum condensation mass fraction predicted by the PR and SRK EOSs is5.7%and 11.5%,and that of total pressure ratio is 0.3%and 3.8%,respectively.The results show that PR EOS can be considered for numerical simulation in engineering practice.Since its physical property calculation results are closer to the actual physical properties while the physical properties change more gently,it has considerable accuracy and numerical stability.展开更多
根据超临界二氧化碳(supercritical carbon dioxide,SCO_(2))的物性特点,调用美国国家标准技术研究所(national institute of standards and technology,NIST)发布的二氧化碳物性参数,开发了SCO_(2)离心压缩机一维设计及性能预测的程序...根据超临界二氧化碳(supercritical carbon dioxide,SCO_(2))的物性特点,调用美国国家标准技术研究所(national institute of standards and technology,NIST)发布的二氧化碳物性参数,开发了SCO_(2)离心压缩机一维设计及性能预测的程序。利用该程序完成了-10 MW SCO_(2)布雷顿循环发电系统中的分流压缩机气动设计以及不同转速下的性能预测,并结合数值计算与流场分析,结果表明:在设计转速下,一维预测结果与三维数值模拟所得的压气机性能结果在小流量区域变化趋势与数值大小吻合较好,但是在堵塞工况点附近两者存在一定的偏差。在其他转速下,一维预测结果与三维数值模拟所得的压气机性能结果吻合较好,表明该一维性能预测能较好预测SCO_(2)离心压缩机的变工况运行特性。展开更多
文摘A kind of direct numerical simulation method suitable for supercritical carbon dioxide jet flow has been discussed in this paper. The form of dimensionless nonconservative compressible Navier-Stokes equations in a two-dimensional cartesian coordinate system is derived in detail. High accurate finite difference compact schemes based on non-uniform grid system are introduced to solve the equations. The simulation results of the three vortex pairing phenomenon of plane mixing layer and a compressible axisymmetric jet flow field show that the discussed numerical simulation method is feasible to calculate the supercritical carbon dioxide jet fluid. And it is found that the difficulties of splitting the convective terms in conservation Navier-Stokes equations, which are brought by the supercritical carbon dioxide fluid pressure state equation, can be avoided by solving the nonconservative compressible Navier-Stokes equations.
文摘This paper aims at using of an approach integrating the fuzzy logic strategy for hypoxemic hypoxia tissue blood carbon dioxide human optimal control problem. To test the efficiency of this strategy, the authors propose a numerical comparison with the direct method by taking the values of determinant parameters of cardiovascular-respiratory system for a 30 years old woman in jogging as her regular physical activity. The results are in good agreement with experimental data.
基金supported by the National Natural Science Foundation of China(Grant No.51304226)the National Key Basic Research Development Program of China(973 Program,Grant No.2014CB239203)
文摘The supercritical carbon dioxide （SC-CO2） jet can break rocks at higher penetration rates and lower threshold pressures than the water jet. The abrasive SC-CO2 jet, formed by adding solid particles into the SC-CO2 jet, is expected to achieve higher operation efficiency in eroding hard rocks and cutting metals. With the computational fluid dynamics numerical simulation method, the characteristics of the flow field of the abrasive SC-CO2 jet are analyzed, as well as the main influencing factors. Results show that the two-phase axial velocities of the abrasive SC-CO2 jet is much higher than those of the abrasive water jet, when the pressure difference across the jet nozzle is held constant at 20 MPa, the optimal standoff distance for the largest particle impact velocity is approximately 5 times of the jet nozzle diameter; the fluid temperature and the volume concentration of the abrasive particles have modest influences on the two-phase velocities, the ambient pressure has a negligible influence when the pressure difference is held constant. Therefore the abrasive SC-CO2 jet is expected to assure more effective erosion and cutting performance. This work can provide guidance for subsequent lab experiments and promote practical applications.
基金Project supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.51221003)the National Natural Science Foundation of China(Grant No.U1562212)
文摘The pure supercritical carbon dioxide（SC-CO2） fracturing prevents the clay from swelling and avoids the water lock as compared with the slick-water fracturing. The CO2 molecule could replace the CH4 adsorbed in organic matter and tiny particles on the clay mineral surface in the formation. This leads to an increased cumulative gas production rate. The SC-CO2 fracturing is an alternative waterless fracturing technique for an effective future development of shale gas reservoirs. Due to its low density and viscosity as compared with the slick-water, it attracts attentions for the proppant transport. In this paper, the two phase flow of the SC-CO2 and the proppant in fractures during the SC-CO2 fracturing is analyzed with the computational fluid dynamics method. The characteristics of the proppant transport by the SC-CO2 fracturing and the slick-water fracturing are compared. Moreover, a sensitivity analysis is also performed to see the influence of various parameters on the proppant transport ability of the SC-CO2 fracturing. It is shown that the proppants in the SC-CO2 and the slick-water have similar distribution characteristics. Reducing the proppant density, the proppant diameter, and the solid volume fraction as well as increasing the injection rate can all have similar filling effects on the fractures. The feasibility of the proppant transport by the SC-CO2 fracturing in fractures is revealed and a guidance is provided for the SC-CO2 fracturing design.
基金supported by National Key Research and Development Project(2018YFB1501003)Natural Science Foundation of Guangdong Province(2017B030308004)。
文摘Molten salt and supercritical carbon dioxide(S-CO_(2))are important high temperature heat transfer media,but molten salt/S-CO_(2) heat exchanger has been seldom reported.In present paper,heat transfer in printed circuit heat exchanger(PCHE)with molten salt and S-CO_(2) is simulated and analyzed.Since S-CO_(2) can be drove along passage wall by strong buoyancy force with large density difference,its heat transfer is enhanced by natural convection.In inlet region,natural convection weakens along flow direction with decreasing Richardson number,and the thermal boundary layer becomes thicker,so local heat transfer coefficient of S-CO_(2) significantly decreases.In outlet region,turbulent kinetic energy gradually increases,and then heat transfer coefficient increases for turbulent heat transfer enhancement.Compared with transcritical CO_(2) with lower inlet temperature,local heat transfer coefficient of S-CO_(2) near inlet is lower for smaller Richardson number,while it will be higher for larger turbulent kinetic energy near outlet.Performance of PCHE is mainly determined by the pressure drop in molten salt passage and the heat transfer resistance in S-CO_(2) passage.When molten salt passage width increases,molten salt pressure drop significantly decreases,and overall heat transfer coefficient slightly changes,so the comprehensive performance of PCHE is improved.As a result,PCHE unit with three semicircular passages and one semi-elliptic passage has better performance.
基金supports of National Natural Science Foundation of China(Grant No.52076079,52206010)Natural Science Foundation of Hebei Province,China(Grant No.E2020502013)Fundamental Research Funds for the Central Universities,China(Grant No.2021MS079)。
文摘The low power consumption of the near-critical compressor is the key factor for the high efficiency of supercritical CO_(2)Brayton cycle.In the numerical simulation of the compressor,the rapid changes in the thermophysical properties of the CO_(2)near the critical point make it difficult to capture the condensation phenomenon.This paper investigates the influence of fluid physical properties on the condensation phenomenon.Firstly,the differences in the physical properties of CO_(2)in the SRK EOS(equation of state),PR EOS,and SW EOS are compared.Then,the simulation of nozzles and compressors were carried out and discussed.Results show that the condensation positions predicted by the three EOSs are basically the same.Compared with SW EOS,the disparities between the maximum condensation mass fraction predicted by the PR and SRK EOSs is5.7%and 11.5%,and that of total pressure ratio is 0.3%and 3.8%,respectively.The results show that PR EOS can be considered for numerical simulation in engineering practice.Since its physical property calculation results are closer to the actual physical properties while the physical properties change more gently,it has considerable accuracy and numerical stability.
文摘根据超临界二氧化碳(supercritical carbon dioxide,SCO_(2))的物性特点,调用美国国家标准技术研究所(national institute of standards and technology,NIST)发布的二氧化碳物性参数,开发了SCO_(2)离心压缩机一维设计及性能预测的程序。利用该程序完成了-10 MW SCO_(2)布雷顿循环发电系统中的分流压缩机气动设计以及不同转速下的性能预测,并结合数值计算与流场分析,结果表明:在设计转速下,一维预测结果与三维数值模拟所得的压气机性能结果在小流量区域变化趋势与数值大小吻合较好,但是在堵塞工况点附近两者存在一定的偏差。在其他转速下,一维预测结果与三维数值模拟所得的压气机性能结果吻合较好,表明该一维性能预测能较好预测SCO_(2)离心压缩机的变工况运行特性。
