To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with dif...To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with different cooling processes were prepared: casting A was prepared in a totally sand mold, and casting B was prepared in a sand mold with two chilling blocks placed on the left and right sides of the mold. Three positions in each casting with different solidification cooling rates were chosen. In-situ SEM tensile experiment was used to observe the dynamic tensile process. Fracture analysis was conducted to study the influence of vermicular and slightly irregular spheroidal graphite on the fracture behavior of heavy section ductile iron. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings all decrease with decreasing cooling rate. With the increase of solidification time, the fracture mechanism of conventional casting A changes from ductile fracture to brittle fracture, and that of casting B with forced cooling changes from ductile fracture to a mixture of ductile-brittle fracture.展开更多
To forecast the as-cast structure and ferrite-austenite phase ratio of 2205 duplex stainless steel(DSS), the effects of cooling rate and forced convection were observed in a high-vacuum resistance furnace in which the...To forecast the as-cast structure and ferrite-austenite phase ratio of 2205 duplex stainless steel(DSS), the effects of cooling rate and forced convection were observed in a high-vacuum resistance furnace in which the forced convection was created by the rotation of the crucible. The as-cast structure of all 2205 DSS samples is full equiaxed grains, and the microstructure consists of a great amount of desirable intra-granular austenite inside the continuous ferrite grain matrix, besides Widmanstatten austenite and grain boundary austenite. The ferrite grain size decreases gradually with the increase in the cooling rates(20 to 60 oC·min-1) or the forced convection, while the ferrite grains of the samples solidified with a strong convection are barely changed when the cooling rate is below 50 oC·min-1. Moreover, a small grain size is beneficial for the austenite formation but the influence is not very obvious under the cooling rates in the range of 5 to 50 oC·min-1. Compared with grain size, the cooling rate has a greater influence on the final ferrite content. A model based on the experimental results is established to predict the ferrite content, which could be approximated by δ(%) = 20.5·exp(c/80.0) + 0.34 d +34.1, where cis the cooling rate in oC·min-1 and d is the grain size in mm. By using this model, the dependence of the final ferrite content on cooling rate and grain size is well described.展开更多
Electron beam welding of QCr0. 8 chromium bronze was ineestigated to improve weld appearance and reduce the size of softened zone of the joints. Effect of forced cooling on weld appearanee and microhardness of the joi...Electron beam welding of QCr0. 8 chromium bronze was ineestigated to improve weld appearance and reduce the size of softened zone of the joints. Effect of forced cooling on weld appearanee and microhardness of the joints was studied by both experiment and numerical simulation. Both welding with and without forced cooling were conducted and analyzed comparatively. The results showed that a quasi steady state temperature.field and a large temperature gradient perpendicular to welding direction could achieved by forced cooling. A consistent weld width throughout the entire weld and smooth surface for both the top and bottom was achieved by forced cooling process. The width of softened zone of the joint was reduced from 2. 6 mm to I mm by forced cooling.展开更多
To identify the effect of solvents and anthracene on the purification of carbazole,the solvent crystallization of carbazole was investigated with xylene,chlorobenzene and tetrachloroethylene(TCE)as solvents under two ...To identify the effect of solvents and anthracene on the purification of carbazole,the solvent crystallization of carbazole was investigated with xylene,chlorobenzene and tetrachloroethylene(TCE)as solvents under two forced circulation cooling(FCC)modes.The co-crystalline experimental data were obtained from runs carried out at different anthracene levels between 1%(mass)and 10%(mass).The results showed that a uniform flake carbazole crystal obtained when using xylene and chlorobenzene under the FCC-1 mode with gradual cooling rate.Nevertheless,fine flake crystals grown under shock cooling of FCC-2 mode.It is beneficial to improving the purity of carbazole with chlorobenzene as solvent under cooling mode of FCC-1.Anthracene could promote the growth of carbazole in solution,and it has a significant influence on the purification of carbazole.展开更多
Forced-air convection cooling of high-power electronic devices is widely used, but it has a problem that a rise in temperature of the air used to cool the upstream devices decreases the cooling capa-bility for the dow...Forced-air convection cooling of high-power electronic devices is widely used, but it has a problem that a rise in temperature of the air used to cool the upstream devices decreases the cooling capa-bility for the downstream devices. In this study we made an experimental apparatus including a memory card array and measured the effect of the rise in temperature of the air on the heat transfer coefficient of the memory cards that were downstream in the air flow. Using these mea-surements, we devised a simple calculation model, called the thermal diffusion layer model, to calculate the heat transfer coefficient of multiple rows of memory cards. The rise in temperature of downstream memory cards due to higher temperature air can be evaluated with a parameter representing the delay of thermal mixing for air. The heat transfer coefficient calculated with the thermal diffusion layer model agreed with our experimental results.展开更多
Thermomechanical Controlled Processing (TMCP) including accelerated cooling after the final hot rolling pass is a well-established technology,widely applied in HSLA steel plate production.However,there are still certa...Thermomechanical Controlled Processing (TMCP) including accelerated cooling after the final hot rolling pass is a well-established technology,widely applied in HSLA steel plate production.However,there are still certain limitations,especially for thicker plate.The rolling schedule includes a long holding period (HP) after the roughing stage to allow the temperature to fall sufficiently for optimised TMCP during finishing.Intermediate Forced Cooling (IFC) applied during the HP can increase productivity by decreasing the required hold time,can restrict austenite grain growth,and can also improve the subsequent strain penetration in thick plate with further metallurgical benefits.Multi-pass plane strain compression (PSC) tests have been performed on the thermomechanical compression (TMC) machine at Sheffield University including different severities of IFC.Clearly it is impossible to simulate all aspects of the temperature and strain gradients present in thick plates in laboratory specimens,and most of the tests were conducted at temperatures and strains calculated by Finite Element modelling as relevant to specific positions through the plate thickness.However,some aspects of the gradients were addressed with tests using cold platens.The results have indeed shown that IFC can shorten the HP and reduce austenite grain growth and its variation across thick plate.展开更多
A static model of the forced cooling of inductors used for induction heating is proposed in order to achieve better coil design to prolong its lifetime and prevent failures.The main aim is to define for the most commo...A static model of the forced cooling of inductors used for induction heating is proposed in order to achieve better coil design to prolong its lifetime and prevent failures.The main aim is to define for the most common copper tubes and inductor geometries an equivalent convection heat transmission coefficient depending upon temperature and pressure of the cooling fluid,in order to model the very complex physics of forced cooling with a strongly simplified method.The model,called 'Line Region Model',considers only the coil's copper tube and its internal surface(interface copper-water)as boundary where the heat exchange conditions are imposed.展开更多
The 300 MW steam turbine installed in Waigaoqiao Power Plant with combined HPIP cylinders of double casing structure is a product of the Shanghai Turbine Works utilizing licensed technology. It has a large heat storag...The 300 MW steam turbine installed in Waigaoqiao Power Plant with combined HPIP cylinders of double casing structure is a product of the Shanghai Turbine Works utilizing licensed technology. It has a large heat storage capacity and good thermal insulation, so the metal temperature of first stage of HP cylinder (FSMTI) may reach 400-450℃ after shut down and it takes 7-8 days to cool to 150℃ by natural cooling, Now with a forced cooling system the cooling time may be reduced to 40 hours, so that the turbine may be opened for repair work in about 5-6 days. The cooling system for #2 unit and test procedure are briefly described below.展开更多
An analysis of atmospheric SW-radiative forcing and local heating/cooling rate is made using a one year temporal and vertical profiles of aerosol and cloud over Yaoundé (11.51°E, 3.83°N). It appears tha...An analysis of atmospheric SW-radiative forcing and local heating/cooling rate is made using a one year temporal and vertical profiles of aerosol and cloud over Yaoundé (11.51°E, 3.83°N). It appears that the direct influence of aerosols on the surface compared to the TOA can be 3 times larger. Annual mean value obtained at 559 mb altitude is +27.74 W/m2 with range from 0 to +43 W/m2. At 904 mb, we obtained an annual mean of ﹣46.22 W/m2 with range from ﹣65 to ﹣9 W/m2. Frequency distribution indicates that more than 95% of ARF are between +10 and +70 W/m2 at 559 mb (upper limit of UL), and more than 85% of ARF are between ﹣70 and ﹣10 W/m2 at 904 mb (upper limit of PBL). This sign change is explained by the fact that the backscattering peaks at the upper limit of the aerosol PBL layer. The maximum CRF is noted at TOA where it reaches ﹣600 W/m2 based on the time interval and the structure of clouds. The highest values occur between 11.50 and 13.50 LST. Clouds lead to a general heating of the entire atmospheric column with a much greater effect near the surface. Aerosols effect on the heating rate profile show strong cooling during the day for the lower atmosphere, with slight heating at the upper atmosphere. This cooling contribution generally increases from the surface and peacks at the upper boundary of aerosol layer where reflectivity is the most important. Depending on the moment of the day, average heating effect of clouds peacks at surface or within the middle troposphere due to the absorption by clouds particles. Vertical profiles deeply evolve exhibiting differences that exceed ﹣3 K/day according to altitude from one hour to another during a given mean solar day.展开更多
Using the algebraic dynamical method, this paper investigates the laser cooling of a moving two-level atom coupled to a cavity field. Analytical solutions of optical forces and the cooling temperatures are obtained. C...Using the algebraic dynamical method, this paper investigates the laser cooling of a moving two-level atom coupled to a cavity field. Analytical solutions of optical forces and the cooling temperatures are obtained. Considering Rb atoms as an example, it finds that the numerical results are relevant to the recent experimental laser cooling investigations.展开更多
The effects of cryogenic cooling on cutting forces in the milling process of AISI 304 stainless steel were investigated experimentally.Cryogenic cooling was achieved by spraying liquid nitrogen to tool,chips and mater...The effects of cryogenic cooling on cutting forces in the milling process of AISI 304 stainless steel were investigated experimentally.Cryogenic cooling was achieved by spraying liquid nitrogen to tool,chips and material interfaces using a pipe with an internal diameter of 1 mm;the flow rate of liquid nitrogen was 5.2 L/min;two cutting directions（climbing and conventional milling）,two machining conditions（dry and cryogenic cooling） and four cutting speeds（80,120,160 and 200 m/min） were used in the milling process.Cryogenic cooling and cutting speed are found to be effective on cutting forces.Cutting forces and torque in cryogenic milling are higher than those in dry milling.Cutting force is increased as the cutting speed is increased.Tool fritter around insert nose radius is the main problem of climb milling method in cryogenic cooling at low cutting speeds.展开更多
To evaluate the effect of actual cooling rate of liquid steel in the ladle on the metallurgical performances of a tundish, a transient and coupled computational model was developed to reveal the flow fields, temperatu...To evaluate the effect of actual cooling rate of liquid steel in the ladle on the metallurgical performances of a tundish, a transient and coupled computational model was developed to reveal the flow fields, temperature fields, residence time distribution of the molten steel and the inclusion removal efficiency in a typical single-strand tundish with given geometry and process parameters. The results showed that, with the decrease of the ladle stream cooling rate, the temperature difference of bulk flow at the outlet of tundish over a normal casting period decreased from 11.3 to 2.6 K, and the dead volume fraction of the tundish decreased from 17.58% to 14. 35%, while the inclusion removal efficiency was increased especially for the inclusions with the diameter less than 50 μm, whose removal ratio could be increased by 20.62%. When the cooling rate was less than 0.3 K · min-1 , however, the variation rates of the three evaluation criterions above declined significantly, which suggested that a critical value existed for the effect of the cooling rate of ladle stream on the tundish performances. The establishment of the critical ladle stream cooling rate should be very important to achieve persistent metallurgical properties of tundish over the whole casting stage, together with the reasonable ladle insulation design.展开更多
The satisfactory performance of electrical equipments depends on their operating temperature. In order to maintain these devices within the safe temperature limits, an effective cooling is needed. High heat transfer r...The satisfactory performance of electrical equipments depends on their operating temperature. In order to maintain these devices within the safe temperature limits, an effective cooling is needed. High heat transfer rate of compact in size and reliable operation are the challenges of a thermal design engineer of electronic equipment. Then, it has been simulated the transient a three-dimensional model to study the heating phenomenon with two assumption values of heat generation. To control for the working of this equipment, cooling process was modeled by choosing one from different cooling technique. Constant low speed fan at one direction of air flow was used for cooling to predict the reducing of heating temperature through working of this equipment. Numerical Solution of finite difference time domain method （FDTD） has been utilized to simulate the temporal and spatial temperature profiles through two processes, which would minimize the solution errors.展开更多
The effects of oceanic forcing on the atmospheric low-frequency wave (LFW for short) in the tropics are analyzed, where ocean and atmosphere are taken as an independent system, respectively. Here oceanic effects are p...The effects of oceanic forcing on the atmospheric low-frequency wave (LFW for short) in the tropics are analyzed, where ocean and atmosphere are taken as an independent system, respectively. Here oceanic effects are parameterized as evaporation-wind feedback (EWF for short) and forcing of SST. Under the modulation of EWF, forcing of SST plays a different role from that without EWF, So LFWs are diabatic waves, forced by the interactions of multiple factors, in the tropics. Key words Atmospheric LFW - Oceanic forcing - EWF - Radiative cooling - SST This paper was supported by “ First Institute of Oceanic Sciences, State Oceanic Administration, State Key Laboratory of Geophysical Fluid Dynamics and Numerical Modeling”.展开更多
The general expressions of the average dissipative and dipole forces acting on a A-configuration three-level atom in an arbitrary light field are derived by means of the optical Bloch equations based on the atomic den...The general expressions of the average dissipative and dipole forces acting on a A-configuration three-level atom in an arbitrary light field are derived by means of the optical Bloch equations based on the atomic density matrix elements, and the general properties of the average dissipative and dipole forces on a three-level atom in the linearly-polarized high-order Bessel beams （HBBs） are analysed. We find a resonant property （with two resonant peaks） of the dissipative force and a non-resonant property （with two pairs of non-resonant peaks） of the dipole force on the three-level atom, which are completely different from those on the two-level atom. Meanwhile we find a saturation effect of the average dissipative force in the HBB, which comes from the saturation of the upper-level population. Our study shows that the general expressions of the average dissipative and dipole forces on the three-level atom will be simplified to those of the two-level atom under the approximation of large detuning. Finally, we study the axial and azimuthal Doppler cooling of atoms in ID optical molasses composed of two counter-propagating HBBs and discuss the azimuthal influence of the HBB on the Doppler cooling limit. We also find that the Doppler limit of atoms in the molasses HBB is slightly below the conventional Doppler limit of hГ/（2kB） due to the orbital angular momentum lh of the HBB.展开更多
In this research, the temperatures of three- dimensional （3D） protruding heaters mounted on a conductive substrate in a horizontal rectangular channel with laminar airflow are related to the independent power dissip...In this research, the temperatures of three- dimensional （3D） protruding heaters mounted on a conductive substrate in a horizontal rectangular channel with laminar airflow are related to the independent power dissipation in each heater by using a matrix G＋ with invariant coefficients, which are dimensionless. These coefficients are defined in this study as the conjugate influence coefficients （g＋） caused by the forced convec- tion-conduction nature of the heaters＇ cooling process. The temperature increase of each heater in the channel is quantified to clearly identify the contributions attributed to the self-heating and power dissipation in the other heaters （both upstream and downstream）. The conjugate coefficients are invariant with the heat generation rate in the array of heaters when assuming a defined geometry, invariable fluid and flow rate, and constant substrate and heater conductivities. The results are numerically obtained by considering three 3D protruding heaters on a twodimensional （2D） array by ANSYS/FluentTM 15.0 software. The conservation equations are solved by a coupled procedure within a single calculation domain comprising of solid and fluid regions and by considering a steady state laminar airflow with constant properties. Some examples are shown, indicating the effects of substrate thermal conductivity and Reynolds number on conjugate influence coefficients.展开更多
Doppler cooling of^(88)Sr atoms is studied in the presence of off-resonant red-detuned fluctuating laser fields.Using a semi-classical approach,we show that the relevant physical quantities in the cooling process,such...Doppler cooling of^(88)Sr atoms is studied in the presence of off-resonant red-detuned fluctuating laser fields.Using a semi-classical approach,we show that the relevant physical quantities in the cooling process,such as optical forces,the damping coefficient,Doppler temperature,and atom number in the trap,are strongly affected by the laser amplitude and phase fluctuations.We find that the Doppler cooling limit is higher than the predicted Doppler theory for non-fluctuating lasers.This implies an additional heating mechanism exists due to the laser fluctuations.Furthermore,our numerical analysis shows that the effect of laser power stability on reducing the number of trapped atoms in a magneto-optical trap is more substantial than the effect of laser linewidth.展开更多
This paper aims to model a subcooled flow boiling in a vertical stainless-steel micro-channel with an upward flow in 1 mm diameter, 40 mm length and 0.325 mm thickness tube. Water has been considered as a working flui...This paper aims to model a subcooled flow boiling in a vertical stainless-steel micro-channel with an upward flow in 1 mm diameter, 40 mm length and 0.325 mm thickness tube. Water has been considered as a working fluid. The heat flux varies from 600 - 750 kW·m-2, input velocity from 1 - 2 m·s-1, and the subcooled temperature varies from 59.6 - 79.6 K. The working pressure and saturation temperature are 1 atm and 372.75 K, respectively. The results show that, the flow boiling keeps the temperature of the channel wall lower and more uniform than a single-phase flow, as long as the flow boiling does not reach the dry-out point. The onset point of dry-out depends on three factors, heat flux, inlet velocity, and subcooled temperature. In addition, the dry-out occurs at a point near the channel inlet with increased heat flux and subcooled temperature. Decreasing the inlet velocity would also cause the dry-out point to shift closer to the inlet of the channel.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51174068 and No.51374086)
文摘To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with different cooling processes were prepared: casting A was prepared in a totally sand mold, and casting B was prepared in a sand mold with two chilling blocks placed on the left and right sides of the mold. Three positions in each casting with different solidification cooling rates were chosen. In-situ SEM tensile experiment was used to observe the dynamic tensile process. Fracture analysis was conducted to study the influence of vermicular and slightly irregular spheroidal graphite on the fracture behavior of heavy section ductile iron. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings all decrease with decreasing cooling rate. With the increase of solidification time, the fracture mechanism of conventional casting A changes from ductile fracture to brittle fracture, and that of casting B with forced cooling changes from ductile fracture to a mixture of ductile-brittle fracture.
基金financially supported by the National Natural Science Foundation of China(No.51227803)the National Key Technology R&D Program of China(No.2012BAE04B02)
文摘To forecast the as-cast structure and ferrite-austenite phase ratio of 2205 duplex stainless steel(DSS), the effects of cooling rate and forced convection were observed in a high-vacuum resistance furnace in which the forced convection was created by the rotation of the crucible. The as-cast structure of all 2205 DSS samples is full equiaxed grains, and the microstructure consists of a great amount of desirable intra-granular austenite inside the continuous ferrite grain matrix, besides Widmanstatten austenite and grain boundary austenite. The ferrite grain size decreases gradually with the increase in the cooling rates(20 to 60 oC·min-1) or the forced convection, while the ferrite grains of the samples solidified with a strong convection are barely changed when the cooling rate is below 50 oC·min-1. Moreover, a small grain size is beneficial for the austenite formation but the influence is not very obvious under the cooling rates in the range of 5 to 50 oC·min-1. Compared with grain size, the cooling rate has a greater influence on the final ferrite content. A model based on the experimental results is established to predict the ferrite content, which could be approximated by δ(%) = 20.5·exp(c/80.0) + 0.34 d +34.1, where cis the cooling rate in oC·min-1 and d is the grain size in mm. By using this model, the dependence of the final ferrite content on cooling rate and grain size is well described.
文摘Electron beam welding of QCr0. 8 chromium bronze was ineestigated to improve weld appearance and reduce the size of softened zone of the joints. Effect of forced cooling on weld appearanee and microhardness of the joints was studied by both experiment and numerical simulation. Both welding with and without forced cooling were conducted and analyzed comparatively. The results showed that a quasi steady state temperature.field and a large temperature gradient perpendicular to welding direction could achieved by forced cooling. A consistent weld width throughout the entire weld and smooth surface for both the top and bottom was achieved by forced cooling process. The width of softened zone of the joint was reduced from 2. 6 mm to I mm by forced cooling.
基金supported by the National Natural Science Foundation of China(21776192,22038008)。
文摘To identify the effect of solvents and anthracene on the purification of carbazole,the solvent crystallization of carbazole was investigated with xylene,chlorobenzene and tetrachloroethylene(TCE)as solvents under two forced circulation cooling(FCC)modes.The co-crystalline experimental data were obtained from runs carried out at different anthracene levels between 1%(mass)and 10%(mass).The results showed that a uniform flake carbazole crystal obtained when using xylene and chlorobenzene under the FCC-1 mode with gradual cooling rate.Nevertheless,fine flake crystals grown under shock cooling of FCC-2 mode.It is beneficial to improving the purity of carbazole with chlorobenzene as solvent under cooling mode of FCC-1.Anthracene could promote the growth of carbazole in solution,and it has a significant influence on the purification of carbazole.
文摘Forced-air convection cooling of high-power electronic devices is widely used, but it has a problem that a rise in temperature of the air used to cool the upstream devices decreases the cooling capa-bility for the downstream devices. In this study we made an experimental apparatus including a memory card array and measured the effect of the rise in temperature of the air on the heat transfer coefficient of the memory cards that were downstream in the air flow. Using these mea-surements, we devised a simple calculation model, called the thermal diffusion layer model, to calculate the heat transfer coefficient of multiple rows of memory cards. The rise in temperature of downstream memory cards due to higher temperature air can be evaluated with a parameter representing the delay of thermal mixing for air. The heat transfer coefficient calculated with the thermal diffusion layer model agreed with our experimental results.
基金Tata Steel Europe Research Development & Technology for their financial and technical support
文摘Thermomechanical Controlled Processing (TMCP) including accelerated cooling after the final hot rolling pass is a well-established technology,widely applied in HSLA steel plate production.However,there are still certain limitations,especially for thicker plate.The rolling schedule includes a long holding period (HP) after the roughing stage to allow the temperature to fall sufficiently for optimised TMCP during finishing.Intermediate Forced Cooling (IFC) applied during the HP can increase productivity by decreasing the required hold time,can restrict austenite grain growth,and can also improve the subsequent strain penetration in thick plate with further metallurgical benefits.Multi-pass plane strain compression (PSC) tests have been performed on the thermomechanical compression (TMC) machine at Sheffield University including different severities of IFC.Clearly it is impossible to simulate all aspects of the temperature and strain gradients present in thick plates in laboratory specimens,and most of the tests were conducted at temperatures and strains calculated by Finite Element modelling as relevant to specific positions through the plate thickness.However,some aspects of the gradients were addressed with tests using cold platens.The results have indeed shown that IFC can shorten the HP and reduce austenite grain growth and its variation across thick plate.
文摘A static model of the forced cooling of inductors used for induction heating is proposed in order to achieve better coil design to prolong its lifetime and prevent failures.The main aim is to define for the most common copper tubes and inductor geometries an equivalent convection heat transmission coefficient depending upon temperature and pressure of the cooling fluid,in order to model the very complex physics of forced cooling with a strongly simplified method.The model,called 'Line Region Model',considers only the coil's copper tube and its internal surface(interface copper-water)as boundary where the heat exchange conditions are imposed.
文摘The 300 MW steam turbine installed in Waigaoqiao Power Plant with combined HPIP cylinders of double casing structure is a product of the Shanghai Turbine Works utilizing licensed technology. It has a large heat storage capacity and good thermal insulation, so the metal temperature of first stage of HP cylinder (FSMTI) may reach 400-450℃ after shut down and it takes 7-8 days to cool to 150℃ by natural cooling, Now with a forced cooling system the cooling time may be reduced to 40 hours, so that the turbine may be opened for repair work in about 5-6 days. The cooling system for #2 unit and test procedure are briefly described below.
文摘An analysis of atmospheric SW-radiative forcing and local heating/cooling rate is made using a one year temporal and vertical profiles of aerosol and cloud over Yaoundé (11.51°E, 3.83°N). It appears that the direct influence of aerosols on the surface compared to the TOA can be 3 times larger. Annual mean value obtained at 559 mb altitude is +27.74 W/m2 with range from 0 to +43 W/m2. At 904 mb, we obtained an annual mean of ﹣46.22 W/m2 with range from ﹣65 to ﹣9 W/m2. Frequency distribution indicates that more than 95% of ARF are between +10 and +70 W/m2 at 559 mb (upper limit of UL), and more than 85% of ARF are between ﹣70 and ﹣10 W/m2 at 904 mb (upper limit of PBL). This sign change is explained by the fact that the backscattering peaks at the upper limit of the aerosol PBL layer. The maximum CRF is noted at TOA where it reaches ﹣600 W/m2 based on the time interval and the structure of clouds. The highest values occur between 11.50 and 13.50 LST. Clouds lead to a general heating of the entire atmospheric column with a much greater effect near the surface. Aerosols effect on the heating rate profile show strong cooling during the day for the lower atmosphere, with slight heating at the upper atmosphere. This cooling contribution generally increases from the surface and peacks at the upper boundary of aerosol layer where reflectivity is the most important. Depending on the moment of the day, average heating effect of clouds peacks at surface or within the middle troposphere due to the absorption by clouds particles. Vertical profiles deeply evolve exhibiting differences that exceed ﹣3 K/day according to altitude from one hour to another during a given mean solar day.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10704031)the National Science Foundation for Fostering Talents in Basic Research of the National Natural Science Foundation of China (Grant No. J0630313)+1 种基金the fundamental Research Fund for Physical and Mathematical of Lanzhou University (Grant No. Lzu05001)the Natural Science Foundation of Gansu,China (Grant No. 3ZS061-A25-035)
文摘Using the algebraic dynamical method, this paper investigates the laser cooling of a moving two-level atom coupled to a cavity field. Analytical solutions of optical forces and the cooling temperatures are obtained. Considering Rb atoms as an example, it finds that the numerical results are relevant to the recent experimental laser cooling investigations.
基金the Scientific and Technological Research Council of Turkey(TUBITAK)for providing the financial support of the cryogenic machining project(Project No.106M473)
文摘The effects of cryogenic cooling on cutting forces in the milling process of AISI 304 stainless steel were investigated experimentally.Cryogenic cooling was achieved by spraying liquid nitrogen to tool,chips and material interfaces using a pipe with an internal diameter of 1 mm;the flow rate of liquid nitrogen was 5.2 L/min;two cutting directions（climbing and conventional milling）,two machining conditions（dry and cryogenic cooling） and four cutting speeds（80,120,160 and 200 m/min） were used in the milling process.Cryogenic cooling and cutting speed are found to be effective on cutting forces.Cutting forces and torque in cryogenic milling are higher than those in dry milling.Cutting force is increased as the cutting speed is increased.Tool fritter around insert nose radius is the main problem of climb milling method in cryogenic cooling at low cutting speeds.
文摘To evaluate the effect of actual cooling rate of liquid steel in the ladle on the metallurgical performances of a tundish, a transient and coupled computational model was developed to reveal the flow fields, temperature fields, residence time distribution of the molten steel and the inclusion removal efficiency in a typical single-strand tundish with given geometry and process parameters. The results showed that, with the decrease of the ladle stream cooling rate, the temperature difference of bulk flow at the outlet of tundish over a normal casting period decreased from 11.3 to 2.6 K, and the dead volume fraction of the tundish decreased from 17.58% to 14. 35%, while the inclusion removal efficiency was increased especially for the inclusions with the diameter less than 50 μm, whose removal ratio could be increased by 20.62%. When the cooling rate was less than 0.3 K · min-1 , however, the variation rates of the three evaluation criterions above declined significantly, which suggested that a critical value existed for the effect of the cooling rate of ladle stream on the tundish performances. The establishment of the critical ladle stream cooling rate should be very important to achieve persistent metallurgical properties of tundish over the whole casting stage, together with the reasonable ladle insulation design.
文摘The satisfactory performance of electrical equipments depends on their operating temperature. In order to maintain these devices within the safe temperature limits, an effective cooling is needed. High heat transfer rate of compact in size and reliable operation are the challenges of a thermal design engineer of electronic equipment. Then, it has been simulated the transient a three-dimensional model to study the heating phenomenon with two assumption values of heat generation. To control for the working of this equipment, cooling process was modeled by choosing one from different cooling technique. Constant low speed fan at one direction of air flow was used for cooling to predict the reducing of heating temperature through working of this equipment. Numerical Solution of finite difference time domain method （FDTD） has been utilized to simulate the temporal and spatial temperature profiles through two processes, which would minimize the solution errors.
基金This paper was supported by" First Institute of Oceanic Sciences, State Oceanic Administration, StateKey Laboratory of Geophys
文摘The effects of oceanic forcing on the atmospheric low-frequency wave (LFW for short) in the tropics are analyzed, where ocean and atmosphere are taken as an independent system, respectively. Here oceanic effects are parameterized as evaporation-wind feedback (EWF for short) and forcing of SST. Under the modulation of EWF, forcing of SST plays a different role from that without EWF, So LFWs are diabatic waves, forced by the interactions of multiple factors, in the tropics. Key words Atmospheric LFW - Oceanic forcing - EWF - Radiative cooling - SST This paper was supported by “ First Institute of Oceanic Sciences, State Oceanic Administration, State Key Laboratory of Geophysical Fluid Dynamics and Numerical Modeling”.
基金supported by the National Natural Science Foundation of China (Grant Nos 10434060 and 10674047)the Natural Science Foundation of the Jiangsu Higher Institutions of China (Grant No 06KJB510020)the Natural Science Foundation of Jiangsu University of China (Grant No 07JDG027)
文摘The general expressions of the average dissipative and dipole forces acting on a A-configuration three-level atom in an arbitrary light field are derived by means of the optical Bloch equations based on the atomic density matrix elements, and the general properties of the average dissipative and dipole forces on a three-level atom in the linearly-polarized high-order Bessel beams （HBBs） are analysed. We find a resonant property （with two resonant peaks） of the dissipative force and a non-resonant property （with two pairs of non-resonant peaks） of the dipole force on the three-level atom, which are completely different from those on the two-level atom. Meanwhile we find a saturation effect of the average dissipative force in the HBB, which comes from the saturation of the upper-level population. Our study shows that the general expressions of the average dissipative and dipole forces on the three-level atom will be simplified to those of the two-level atom under the approximation of large detuning. Finally, we study the axial and azimuthal Doppler cooling of atoms in ID optical molasses composed of two counter-propagating HBBs and discuss the azimuthal influence of the HBB on the Doppler cooling limit. We also find that the Doppler limit of atoms in the molasses HBB is slightly below the conventional Doppler limit of hГ/（2kB） due to the orbital angular momentum lh of the HBB.
文摘In this research, the temperatures of three- dimensional （3D） protruding heaters mounted on a conductive substrate in a horizontal rectangular channel with laminar airflow are related to the independent power dissipation in each heater by using a matrix G＋ with invariant coefficients, which are dimensionless. These coefficients are defined in this study as the conjugate influence coefficients （g＋） caused by the forced convec- tion-conduction nature of the heaters＇ cooling process. The temperature increase of each heater in the channel is quantified to clearly identify the contributions attributed to the self-heating and power dissipation in the other heaters （both upstream and downstream）. The conjugate coefficients are invariant with the heat generation rate in the array of heaters when assuming a defined geometry, invariable fluid and flow rate, and constant substrate and heater conductivities. The results are numerically obtained by considering three 3D protruding heaters on a twodimensional （2D） array by ANSYS/FluentTM 15.0 software. The conservation equations are solved by a coupled procedure within a single calculation domain comprising of solid and fluid regions and by considering a steady state laminar airflow with constant properties. Some examples are shown, indicating the effects of substrate thermal conductivity and Reynolds number on conjugate influence coefficients.
文摘Doppler cooling of^(88)Sr atoms is studied in the presence of off-resonant red-detuned fluctuating laser fields.Using a semi-classical approach,we show that the relevant physical quantities in the cooling process,such as optical forces,the damping coefficient,Doppler temperature,and atom number in the trap,are strongly affected by the laser amplitude and phase fluctuations.We find that the Doppler cooling limit is higher than the predicted Doppler theory for non-fluctuating lasers.This implies an additional heating mechanism exists due to the laser fluctuations.Furthermore,our numerical analysis shows that the effect of laser power stability on reducing the number of trapped atoms in a magneto-optical trap is more substantial than the effect of laser linewidth.
文摘This paper aims to model a subcooled flow boiling in a vertical stainless-steel micro-channel with an upward flow in 1 mm diameter, 40 mm length and 0.325 mm thickness tube. Water has been considered as a working fluid. The heat flux varies from 600 - 750 kW·m-2, input velocity from 1 - 2 m·s-1, and the subcooled temperature varies from 59.6 - 79.6 K. The working pressure and saturation temperature are 1 atm and 372.75 K, respectively. The results show that, the flow boiling keeps the temperature of the channel wall lower and more uniform than a single-phase flow, as long as the flow boiling does not reach the dry-out point. The onset point of dry-out depends on three factors, heat flux, inlet velocity, and subcooled temperature. In addition, the dry-out occurs at a point near the channel inlet with increased heat flux and subcooled temperature. Decreasing the inlet velocity would also cause the dry-out point to shift closer to the inlet of the channel.
