Combining the mean field Pozhar-Gubbins(PG)theory and the weighted density approximation,a novel method for local thermal conductivity of inhomogeneous fluids is proposed.The correlation effect that is beyond the mean...Combining the mean field Pozhar-Gubbins(PG)theory and the weighted density approximation,a novel method for local thermal conductivity of inhomogeneous fluids is proposed.The correlation effect that is beyond the mean field treatment is taken into account by the simulation-based empirical correlations.The application of this method to confined argon in slit pore shows that its prediction agrees well with the simulation results,and that it performs better than the original PG theory as well as the local averaged density model(LADM).In its further application to the nano-fluidic films,the influences of fluid parameters and pore parameters on the thermal conductivity are calculated and investigated.It is found that both the local thermal conductivity and the overall thermal conductivity can be significantly modulated by these parameters.Specifically,in the supercritical states,the thermal conductivity of the confined fluid shows positive correlation to the bulk density as well as the temperature.However,when the bulk density is small,the thermal conductivity exhibits a decrease-increase transition as the temperature is increased.This is also the case in which the temperature is low.In fact,the decrease-increase transition in both the small-bulk-density and low-temperature cases arises from the capillary condensation in the pore.Furthermore,smaller pore width and/or stronger adsorption potential can raise the critical temperature for condensation,and then are beneficial to the enhancement of the thermal conductivity.These modulation behaviors of the local thermal conductivity lead immediately to the significant difference of the overall thermal conductivity in different phase regions.展开更多
In this study,?a 2-D MHD free convection incompressible electrically induced boundary layer analysis on a water/nano-fluidic mixture. The ODE solution is numerically analyzed with a Runge-Kutta model as the thermophys...In this study,?a 2-D MHD free convection incompressible electrically induced boundary layer analysis on a water/nano-fluidic mixture. The ODE solution is numerically analyzed with a Runge-Kutta model as the thermophysical properties on a magnetic variation as well as temperature ranges of buoyancy effects on the T and V profiles and the wall force friction on the flow is also studied. The temperature and velocity gradients have a significant differential change is been observed in this study.展开更多
Considering the issues of energy saving and environment protection,the performance of refrigeration systems requires to be improved.In recent years,nano-fluids have attracted greatly attention from the researchers due...Considering the issues of energy saving and environment protection,the performance of refrigeration systems requires to be improved.In recent years,nano-fluids have attracted greatly attention from the researchers due to their outstanding thermal characteristics.In this work,the published investigations on the preparation and characterization of nano-fluids have been discussed at first.Furthermore,the key thermo-physical properties of nano-fluids,such as thermal conductivity,viscosity,specific heat and density have been summarized.Finally,the performance enhancements in different types of refrigeration systems by using nano-fluids have been reviewed.It is concluded that nano-fluids as refrigerant,lubricant or secondary fluid have wide potential application in refrigeration systems.展开更多
The present study discusses the thermal performance of the receiver tube,which contains a wall with various fin shapes in the parabolic trough collector.Inserted fins and bulge surfaces of the inner wall of the receiv...The present study discusses the thermal performance of the receiver tube,which contains a wall with various fin shapes in the parabolic trough collector.Inserted fins and bulge surfaces of the inner wall of the receiver tube increase the turbulent fluid flow.In pursuance of uniform distribution of heat transfer,various fin shapes such as square-shape,circle-shape,triangle-shape,and combined square-circle shapes were inserted,examined,and compared.A study of the temperature differences and fluid flow is meaningful for this project therefore finite volume method was used to investigate heat transfer.Also,hybrid Nano-Fluid AL_(2)O_(3-)CuO,TiO_(2-)Cu,and AgMgO were applied to increase thermal diffusivity.When the combined square-circle-shaped fin was inserted,the thermal peak of fluid flow in the receiver tube was lower than the other studied fin shapes by almost 1%.Besides,the hybrid nano-fluid Ag-MgO Syltherm-oil-800 has lower thermal waste in comparison to others by more than 3%.展开更多
基金Project supported by the Fundamental Research Fund for the Central Universities of Chinathe Research Project for Independently Cultivate Talents of Hebei Agricultural University (Grant No.ZY2023007)。
文摘Combining the mean field Pozhar-Gubbins(PG)theory and the weighted density approximation,a novel method for local thermal conductivity of inhomogeneous fluids is proposed.The correlation effect that is beyond the mean field treatment is taken into account by the simulation-based empirical correlations.The application of this method to confined argon in slit pore shows that its prediction agrees well with the simulation results,and that it performs better than the original PG theory as well as the local averaged density model(LADM).In its further application to the nano-fluidic films,the influences of fluid parameters and pore parameters on the thermal conductivity are calculated and investigated.It is found that both the local thermal conductivity and the overall thermal conductivity can be significantly modulated by these parameters.Specifically,in the supercritical states,the thermal conductivity of the confined fluid shows positive correlation to the bulk density as well as the temperature.However,when the bulk density is small,the thermal conductivity exhibits a decrease-increase transition as the temperature is increased.This is also the case in which the temperature is low.In fact,the decrease-increase transition in both the small-bulk-density and low-temperature cases arises from the capillary condensation in the pore.Furthermore,smaller pore width and/or stronger adsorption potential can raise the critical temperature for condensation,and then are beneficial to the enhancement of the thermal conductivity.These modulation behaviors of the local thermal conductivity lead immediately to the significant difference of the overall thermal conductivity in different phase regions.
文摘In this study,?a 2-D MHD free convection incompressible electrically induced boundary layer analysis on a water/nano-fluidic mixture. The ODE solution is numerically analyzed with a Runge-Kutta model as the thermophysical properties on a magnetic variation as well as temperature ranges of buoyancy effects on the T and V profiles and the wall force friction on the flow is also studied. The temperature and velocity gradients have a significant differential change is been observed in this study.
基金National Natural Science Foundation of China(No.51906013)The Pyramid Talent Training Project of Beijing University of Civil Engineering and Architecture,China(JDYC20200316)。
文摘Considering the issues of energy saving and environment protection,the performance of refrigeration systems requires to be improved.In recent years,nano-fluids have attracted greatly attention from the researchers due to their outstanding thermal characteristics.In this work,the published investigations on the preparation and characterization of nano-fluids have been discussed at first.Furthermore,the key thermo-physical properties of nano-fluids,such as thermal conductivity,viscosity,specific heat and density have been summarized.Finally,the performance enhancements in different types of refrigeration systems by using nano-fluids have been reviewed.It is concluded that nano-fluids as refrigerant,lubricant or secondary fluid have wide potential application in refrigeration systems.
文摘The present study discusses the thermal performance of the receiver tube,which contains a wall with various fin shapes in the parabolic trough collector.Inserted fins and bulge surfaces of the inner wall of the receiver tube increase the turbulent fluid flow.In pursuance of uniform distribution of heat transfer,various fin shapes such as square-shape,circle-shape,triangle-shape,and combined square-circle shapes were inserted,examined,and compared.A study of the temperature differences and fluid flow is meaningful for this project therefore finite volume method was used to investigate heat transfer.Also,hybrid Nano-Fluid AL_(2)O_(3-)CuO,TiO_(2-)Cu,and AgMgO were applied to increase thermal diffusivity.When the combined square-circle-shaped fin was inserted,the thermal peak of fluid flow in the receiver tube was lower than the other studied fin shapes by almost 1%.Besides,the hybrid nano-fluid Ag-MgO Syltherm-oil-800 has lower thermal waste in comparison to others by more than 3%.
