The present work is devoted to investigating heat transfer and fluid flow in a two dimensional square open cavity containing a heated circular cylinder at the centre. A constant heat flux is set at the left sidewall;h...The present work is devoted to investigating heat transfer and fluid flow in a two dimensional square open cavity containing a heated circular cylinder at the centre. A constant heat flux is set at the left sidewall;high and low temperatures are fixed at the bottom and top walls of the cavity respectively. The right side of the cavity is open. Galerkin Weighted Residual Finite Element Analysis is used to visualize the heat transfer and fluid flow solving two-dimensional governing mass, momentum and energy equations for steady state, heat transfer and fluid flow in presence of magnetic field in side an open square cavity. A uniformly heated circular cylinder is placed at the centre of the cavity as a heat source. To find the effects of Rayleigh number (Ra) on the thermal fields and fluid flow in presence of magnetic field and a heated circular cylinder as heat source by visualization and line graphs is the objective of this study. Numerical results are presented in graphical and tabular form. The study is conducted for different values of Rayleigh number, some fixed Hartmann numbers (Ha) and heat flux (q). In the conclusion it has been observed that the temperature field and fluid flow pattern are functions of the parameters Rayleigh number and Hartmann number.展开更多
We study the detection of accelerator neutrinos produced at the China Spallation Neutron Source （CSNS）. Using the code FLUKA, we have simulated the production of neutrinos in a proton beam on a tungsten target and o...We study the detection of accelerator neutrinos produced at the China Spallation Neutron Source （CSNS）. Using the code FLUKA, we have simulated the production of neutrinos in a proton beam on a tungsten target and obtained the yield efficiency, numerical flux, and average energy of different flavors of neutrinos. Furthermore, detection of these accelerator neutrinos is investigated in two reaction channels： neutrino-electron reactions and neutrino-carbon reactions. The expected numbers of different flavors of neutrinos have also been calculated.展开更多
In order to uncover a possible influence on the Earth's climate, we need a much longer time series, i.e., the total solar irradiance (TSI) which is also an interesting issue in its own right in solar physics. By c...In order to uncover a possible influence on the Earth's climate, we need a much longer time series, i.e., the total solar irradiance (TSI) which is also an interesting issue in its own right in solar physics. By comparing different solar indices associated with TSI during the period 1979 to 2009, several empirical models in the TSI are presented. We verify that the reconstruction model based on the three variables: sunspot number, sunspot area, and solar 10.7 cm radio flux, is the best one. As demonstrated by model calculations, the history of TSI was reconstructed back to 1947 based on 3-indices and to 1874 based on 2-indices, respectively. The reason that the reduced irradiance on the trough during 2006 to 2009 lasts long may be due to the about 85-year cycle of solar activity, which modulates the intensity of the 11-year cycle (Schwabe cycles), possesses a considerable potential to produce an effective reducing, and holds on a steadily lower level of irradiance.展开更多
Gas flows and particle mass flux were measured and clutriation experimentswere conducted in two cold test models of vortexing fluidized bed(VFB).The experimen-tal results show that the secondary air injected tangentia...Gas flows and particle mass flux were measured and clutriation experimentswere conducted in two cold test models of vortexing fluidized bed(VFB).The experimen-tal results show that the secondary air injected tangentially creates strong vortexes,estab-lishes particle suspension layers and internal circulation,and suppresses the elutriation offine particles greatly.The vortexing fluidized bed combustion has bright prospect bccauseof its much higher combustion efficiency and desulphidation efficiency than bubblingfluidized bed combustion due to long particle residence time and high slip velocity betweengas and solid,and its simpler configuration and lower cost than circulating fluidized bedcombustion.展开更多
Fifty years ago, Hans A. Panofsky published a paper entitled Determination of stress from wind and temperature measurements. In his famous paper, he presented a new profile function for the mean horizontal wind speed ...Fifty years ago, Hans A. Panofsky published a paper entitled Determination of stress from wind and temperature measurements. In his famous paper, he presented a new profile function for the mean horizontal wind speed under the condition of diabatic stratification that includes his integral similarity function. With his integral similarity function, he opened the door for Monin-Obukhov scaling in a wide range of micrometeorological and microclimatological applications. In a historic survey ranging from the sixties of the past century down to the present days, we present integral similarity functions for momentum, sensible heat, and water vapor for both unstable and stable stratification, where on the one hand free convection condition and on the other hand strongly stable stratification are addressed.展开更多
There are more and more researches on heat transfer characteristics and prediction of supercritical CO_(2).The method of adding adiabatic section before and after heating section is usually adopted in these researches...There are more and more researches on heat transfer characteristics and prediction of supercritical CO_(2).The method of adding adiabatic section before and after heating section is usually adopted in these researches to ensure that the fluid entering the heating section is no longer affected by boundary layer,but the appropriate length range of adiabatic section and the influence of entrance effect are not discussed.However,some studies show that the entrance effect would affect the heat transfer in mini tubes.This paper uses the commercial CFD code FLUENT 19.0 to numerically study the heat transfer of supercritical CO_(2) in a mini tube under different working conditions(such as Re_(in),P_(in),q_(w) and flow direction)and the lengths of the adiabatic section(l_(as)/d).The entrance effects on heat transfer is more pronounced when Re_(in) is within the transition state and wall heat flux is relatively high,the resulting heat transfer deterioration causes T_(w,x) and h_(w,x) to rise sharply.As the adiabatic section increases,the location at which the heat exchange deteriorates moves to the entrance of the heating section and eventually leaves.The buoyancy effect and flow acceleration effect caused by the sharp change of physical properties are analyzed,and the dimensionless velocity distribution at the inlet of the heating section in different adiabatic sections is compared.It is proved that the entrance effect has an influence on the convection heat transfer of supercritical CO_(2) in mini tubes.The interaction reflected by wall shear stress between boundary layer development and drastic changes in physical properties is the cause of heat transfer deterioration.展开更多
文摘The present work is devoted to investigating heat transfer and fluid flow in a two dimensional square open cavity containing a heated circular cylinder at the centre. A constant heat flux is set at the left sidewall;high and low temperatures are fixed at the bottom and top walls of the cavity respectively. The right side of the cavity is open. Galerkin Weighted Residual Finite Element Analysis is used to visualize the heat transfer and fluid flow solving two-dimensional governing mass, momentum and energy equations for steady state, heat transfer and fluid flow in presence of magnetic field in side an open square cavity. A uniformly heated circular cylinder is placed at the centre of the cavity as a heat source. To find the effects of Rayleigh number (Ra) on the thermal fields and fluid flow in presence of magnetic field and a heated circular cylinder as heat source by visualization and line graphs is the objective of this study. Numerical results are presented in graphical and tabular form. The study is conducted for different values of Rayleigh number, some fixed Hartmann numbers (Ha) and heat flux (q). In the conclusion it has been observed that the temperature field and fluid flow pattern are functions of the parameters Rayleigh number and Hartmann number.
基金Supported by National Natural Science Foundation of China(11205185,11175020)
文摘We study the detection of accelerator neutrinos produced at the China Spallation Neutron Source （CSNS）. Using the code FLUKA, we have simulated the production of neutrinos in a proton beam on a tungsten target and obtained the yield efficiency, numerical flux, and average energy of different flavors of neutrinos. Furthermore, detection of these accelerator neutrinos is investigated in two reaction channels： neutrino-electron reactions and neutrino-carbon reactions. The expected numbers of different flavors of neutrinos have also been calculated.
基金supported by the National Natural Science Foundation of China (Grant No. 10978007)the Excellent Scientists Training Program of Beijing
文摘In order to uncover a possible influence on the Earth's climate, we need a much longer time series, i.e., the total solar irradiance (TSI) which is also an interesting issue in its own right in solar physics. By comparing different solar indices associated with TSI during the period 1979 to 2009, several empirical models in the TSI are presented. We verify that the reconstruction model based on the three variables: sunspot number, sunspot area, and solar 10.7 cm radio flux, is the best one. As demonstrated by model calculations, the history of TSI was reconstructed back to 1947 based on 3-indices and to 1874 based on 2-indices, respectively. The reason that the reduced irradiance on the trough during 2006 to 2009 lasts long may be due to the about 85-year cycle of solar activity, which modulates the intensity of the 11-year cycle (Schwabe cycles), possesses a considerable potential to produce an effective reducing, and holds on a steadily lower level of irradiance.
文摘Gas flows and particle mass flux were measured and clutriation experimentswere conducted in two cold test models of vortexing fluidized bed(VFB).The experimen-tal results show that the secondary air injected tangentially creates strong vortexes,estab-lishes particle suspension layers and internal circulation,and suppresses the elutriation offine particles greatly.The vortexing fluidized bed combustion has bright prospect bccauseof its much higher combustion efficiency and desulphidation efficiency than bubblingfluidized bed combustion due to long particle residence time and high slip velocity betweengas and solid,and its simpler configuration and lower cost than circulating fluidized bedcombustion.
基金the National Science Foundation for funding Dillon Amaya’s project work in summer 2012 through the Research Experience for Undergraduates(REU)Program,grant AGS1005265
文摘Fifty years ago, Hans A. Panofsky published a paper entitled Determination of stress from wind and temperature measurements. In his famous paper, he presented a new profile function for the mean horizontal wind speed under the condition of diabatic stratification that includes his integral similarity function. With his integral similarity function, he opened the door for Monin-Obukhov scaling in a wide range of micrometeorological and microclimatological applications. In a historic survey ranging from the sixties of the past century down to the present days, we present integral similarity functions for momentum, sensible heat, and water vapor for both unstable and stable stratification, where on the one hand free convection condition and on the other hand strongly stable stratification are addressed.
文摘There are more and more researches on heat transfer characteristics and prediction of supercritical CO_(2).The method of adding adiabatic section before and after heating section is usually adopted in these researches to ensure that the fluid entering the heating section is no longer affected by boundary layer,but the appropriate length range of adiabatic section and the influence of entrance effect are not discussed.However,some studies show that the entrance effect would affect the heat transfer in mini tubes.This paper uses the commercial CFD code FLUENT 19.0 to numerically study the heat transfer of supercritical CO_(2) in a mini tube under different working conditions(such as Re_(in),P_(in),q_(w) and flow direction)and the lengths of the adiabatic section(l_(as)/d).The entrance effects on heat transfer is more pronounced when Re_(in) is within the transition state and wall heat flux is relatively high,the resulting heat transfer deterioration causes T_(w,x) and h_(w,x) to rise sharply.As the adiabatic section increases,the location at which the heat exchange deteriorates moves to the entrance of the heating section and eventually leaves.The buoyancy effect and flow acceleration effect caused by the sharp change of physical properties are analyzed,and the dimensionless velocity distribution at the inlet of the heating section in different adiabatic sections is compared.It is proved that the entrance effect has an influence on the convection heat transfer of supercritical CO_(2) in mini tubes.The interaction reflected by wall shear stress between boundary layer development and drastic changes in physical properties is the cause of heat transfer deterioration.
