The flow and heat transfer characteristics of n-decane in the sub-millimeter spiral tube(SMST) at supercritical pressure(p = 3 MPa) are studied by the RNG k-ε numerical model in this paper. The effects of various Rey...The flow and heat transfer characteristics of n-decane in the sub-millimeter spiral tube(SMST) at supercritical pressure(p = 3 MPa) are studied by the RNG k-ε numerical model in this paper. The effects of various Reynolds numbers(Re) and structural parameters pitch(s) and spiral diameter(D) are analyzed.Results indicate that the average Nusselt numberNu and friction factorNu increase with an increase in Re, and decrease with an increase in D/d(tube diameter). In terms of the structural parameter s/d, it is found that as s/d increases, the Nu first increase, and then decrease. and the critical structural parameter is s/d = 4. Compared with the straight tube, the SMST can improve Nu by 34.8% at best, while it can improve Nu by 102.1% at most. In addition, a comprehensive heat transfer coefficient is applied to analyze the thermodynamic properties of SMST. With the optimal structural parameters of D/d = 6 and s/d = 4, the comprehensive heat transfer factor of supercritical pressure hydrocarbon fuel in the SMST can reach 1.074. At last, correlations of the average Nusselt number and friction factor are developed to predict the flow and heat transfer of n-decane at supercritical pressure.展开更多
With the advent of the 5G era,the design of electronic equipment is developing towards thinness,intelligence and multi-function,which requires higher cooling performance of the equipment.Micro-channel heat sink is pro...With the advent of the 5G era,the design of electronic equipment is developing towards thinness,intelligence and multi-function,which requires higher cooling performance of the equipment.Micro-channel heat sink is promising for the heat dissipation of super-thin electronic equipment.In this study,thermal resistance theoretical model of the micro-channel heat sink was first established.Then,fabrication process of the micro-channel heat sink was introduced.Subsequently,heat transfer performance of the fabricated micro-channel heat sink was tested through the developed testing platform.Results show that the developed micro-channel heat sink has more superior heat dissipation performance over conventional metal solid heat sink and it is well suited for high power LEDs application.Moreover,the micro-channel structures in the heat sink were optimized by orthogonal test.Based on the orthogonal optimization,heat dissipation performance of the micro-channel radiator was further improved.展开更多
The divertor target components for the Chinese fusion engineering test reactor(CFETR)and the future experimental advanced superconducting tokamak(EAST)need to remove a heat flux of up to20 MW m-2.In view of such a hig...The divertor target components for the Chinese fusion engineering test reactor(CFETR)and the future experimental advanced superconducting tokamak(EAST)need to remove a heat flux of up to20 MW m-2.In view of such a high heat flux removal requirement,this study proposes a conceptual design for a flat-tile divertor target based on explosive welding and brazing technology.Rectangular water-cooled channels with a special thermal transfer structure(TTS)are designed in the heat sink to improve the flat-tile divertor target’s heat transfer performance(HTP).The parametric design and optimization methods are applied to study the influence of the TTS variation parameters,including height(H),width(W*),thickness(T),and spacing(L),on the HTP.The research results show that the flat-tile divertor target’s HTP is sensitive to the TTS parameter changes,and the sensitivity is T>L>W*>H.The HTP first increases and then decreases with the increase of T,L,and W*and gradually increases with the increase of H.The optimal design parameters are as follows:H=5.5 mm,W*=25.8 mm,T=2.2 mm,and L=9.7 mm.The HTP of the optimized flat-tile divertor target at different flow speeds and tungsten tile thicknesses is studied using the numerical simulation method.A flat-tile divertor mock-up is developed according to the optimized parameters.In addition,high heat flux(HHF)tests are performed on an electron beam facility to further investigate the mock-up HTP.The numerical simulation calculation results show that the optimized flat-tile divertor target has great potential for handling the steady-state heat load of 20 MW m-2under the tungsten tile thickness<5 mm and the flow speed7 m s^(-1).The heat transfer efficiency of the flat-tile divertor target with rectangular cooling channels improves by13%and30%compared to that of the flat-tile divertor target with circular cooling channels and the ITER-like monoblock,respectively.The HHF tests indicate that the flat-tile divertor mock-up can successfully withstand 1000 cycles of20 MW m-2of heat load without visible deformation,damage,and HTP degradation.The surface temperature of the flat-tile divertor mock-up at the 1000th cycle is only930℃.The flat-tile divertor target’s HTP is greatly improved by the parametric design and optimization method,and is better than the ITER-like monoblock and the flat-tile mock-up for the WEST divertor.This conceptual design is currently being applied to the engineering design of the CFETR and EAST flat-tile divertors.展开更多
In this paper,we take the mid-temperature gravity heat pipe exchanger as the research object,simulate the fluid flow field,temperature field and the working state of heat pipe in the heat exchanger by Fluent software....In this paper,we take the mid-temperature gravity heat pipe exchanger as the research object,simulate the fluid flow field,temperature field and the working state of heat pipe in the heat exchanger by Fluent software.The effects of different operating parameters and fin parameters on the heat transfer performance of heat exchangers are studied.The results show that the heat transfer performance of the mid-temperature gravity heat pipe exchanger is the best when the fin spacing is between 5 mm and 6 mm,the height of the heat pipe is between 12 mm and 13 mm,and the inlet velocity of the fluid is between 2.5 m/s to 3 m/s.展开更多
Considering utilization of the original chromium-bronze material, two processing techniques including hydraulic expansion and high temperature vacuum welding were proposed for the optimization of heat-sink structure i...Considering utilization of the original chromium-bronze material, two processing techniques including hydraulic expansion and high temperature vacuum welding were proposed for the optimization of heat-sink structure in EAST. The heat transfer performance of heat-sink with or without cooling tube was calculated and different types of connection between tube and heat-sink were compared by conducting a special test. It is shown from numerical analysis that the diameter of heat-sink channel can be reduced from 12 mm to 10 mm. Compared with the original sample, the thermal contact resistance between tube and heat-sink for welding sample can reduce the heat transfer performance by 10%, while by 20% for the hydraulic expansion sample. However, the welding technique is more complicated and expensive than hydraulic expansion technique. Both the processing technique and the heat transfer performance of heat-sink prototype should be further considered for the optimization of heat-sink structure in EAST.展开更多
In order to improve the performance of vehicle radiators, a two-dimensional heat transfer steady-state model of the radiator was set up. The influence of the structural parameters (axial ratio) of the heat exchange tu...In order to improve the performance of vehicle radiators, a two-dimensional heat transfer steady-state model of the radiator was set up. The influence of the structural parameters (axial ratio) of the heat exchange tube on the windward side on the heat transfer performance of the radiator was studied. With the increase of the axial ratio of the heat exchange tube on the windward side, the heat exchange capacity of the heat exchange tube surface slightly decreases. The heat exchange area increases significantly, which increases the total heat exchange of the radiator and improves the heat transfer performance of the radiator. When the axial ratio increases from 1.0 to 2.0, the average surface heat transfer capacity decreases from 5664.16</span><span style="font-family:""> </span><span style="font-family:Verdana;">W/m<sup>2</sup> to 5623.57</span><span style="font-family:""> </span><span style="font-family:Verdana;">W/m<sup>2</sup>.展开更多
Compared with a conventional single section two-phase closed thermosyphon (TPCT) wellbore, a two-section TPCT wellbore has better heat transfer performance, which may improve the temperature distribution of fluid in...Compared with a conventional single section two-phase closed thermosyphon (TPCT) wellbore, a two-section TPCT wellbore has better heat transfer performance, which may improve the temperature distribution of fluid in wellbores, increase the temperature of fluid in wellheads and even more effectively reduce the failure rate of conventional TPCT wellbores. Heat transfer performance of two-section TPCT wellbores is affected by working medium, combination mode and oil flow rate. Different working media are introduced into the upper and lower TPCTs, which may achieve a better match between the working medium and the temperature field in the wellbores. Interdependence exists between the combination mode and the flow rate of the oil, which affects the heat transfer performance of a two-section TPCT wellbore. The experimental results show that a two-section TPCT wellbore, with equal upper and lower TPCTs respectively filled with Freon and methanol, has the best heat transfer performance when the oil flow rate is 200 L/h.展开更多
In the present work,a numerical investigation on the coaxial shallow borehole heat exchanger based on Com-putational Fluid Dynamics(CFD)technique in Hefei city of China has been performed.The effects of design paramet...In the present work,a numerical investigation on the coaxial shallow borehole heat exchanger based on Com-putational Fluid Dynamics(CFD)technique in Hefei city of China has been performed.The effects of design parameters,including inlet flow rate,inlet fluid temperature,inner pipe material and outer pipe diameter,on the heat transfer performance were systematically studied.Besides,the thermal behavior along the pipe has been carefully examined with focus on the thermal short-circuiting phenomena.When the fluid inlet velocity is less than the critical value,the turbulence intensity increases and the Nusselt number increases with the inlet flow rate increasing.However,there is sufficient time for heat transfer between the fluid in inner pipe and outer pipe because of low flow rates,leading to large heat loss,i.e.,thermal short-circuiting phenomenon.It is found that with the inlet flow rate increasing,the heat transfer increases first and then decreases,and the rate of reduction slows down gradually.When the inlet flow rate increases,the pumping power undergoes exponential growth.As the inlet temperature increasing,the heat transfer decreases almost linearly.Moreover,when the soil temperature at the top of the casing is lower than that of the fluid in the casing,heat is transferred from the fluid in the casing to the soil,and the heat loss increases with the increase of the inlet fluid temperature.The material of inner pipe with high heat conductivity would result in large heat loss under the influence of thermal short-circuiting.The heat load increases while the pumping power required decreases with the increasing of outer pipe diameter.This study is very beneficial for the coaxial shallow borehole exchanger designs and energy conservation of buildings.展开更多
The winds will greatly weaken the cooling performance of indirect dry cooling system with twin towers.The exterior windbreakers are recommended to restrain the wind adverse effects in this paper.The macro heat exchang...The winds will greatly weaken the cooling performance of indirect dry cooling system with twin towers.The exterior windbreakers are recommended to restrain the wind adverse effects in this paper.The macro heat exchanger model was adopted to simulate the heat exchange between circulating water and ambient air.The performances of natural draft dry cooling system(NDDCS)with and without exterior windbreakers were numerically studied.The pressure,velocity and temperature distribution of cooling air in wind angles of 0°,45°and 90°was obtained and presented.The results show that in all wind directions,the performances for lateral sector of towers with windbreakers are significantly improved,but the low-pressure zone appears unexpectedly for the rear sectors,which reduces the air flow rate.The cooling performances of the twin towers with or without windbreakers decrease at first but then recover with the wind velocity increasing.Besides,the optimal flow and heat transfer performances appear in the wind angle of 0°.The cooling performances can be significantly improved in all three wind directions due to windbreaker configuration.展开更多
This paper presents three-dimensional numerical simulations with the established realizable k-εmodel to clarify the underlying and interacting mechanisms between the film cooling and the internal cooling.On the one h...This paper presents three-dimensional numerical simulations with the established realizable k-εmodel to clarify the underlying and interacting mechanisms between the film cooling and the internal cooling.On the one hand,the effects of three different internal cooling channels,i.e.,smooth channel,continuous ribbed channel,and truncated ribbed channel,on the film cooling effectiveness and the discharge coefficients are investigated.On the other hand,the influences of three different film cooling holes,i.e.,cylindrical hole,two elliptical holes and two circular-to-elliptical holes,on the heat transfer performances and pressure loss of the internal cooling channel are revealed.Especially,the suction effects of the film cooling holes are analyzed through setting up baselines with only internal cooling channels.Results show that the placement of ribs in the internal channel has different influences on the film cooling effectiveness with respect to different hole shapes depending on the blowing ratio.The discharge coefficient of the film hole can be improved by introducing ribs to the internal channel.Suction of film hole is helpful for enhancing the heat transfer performance and reducing the pressure loss of the internal channel.Besides,ribs instead of the suction effect of film hole play a major role to enhance the heat transfer performance in the internal cooling channel.展开更多
Spray cooling has proved its superior heat transfer performance in removing high heat flux for ground applications. However, the dissipation of vapor liquid mixture from the heat sur- face and the closed-loop circulat...Spray cooling has proved its superior heat transfer performance in removing high heat flux for ground applications. However, the dissipation of vapor liquid mixture from the heat sur- face and the closed-loop circulation of the coolant are two challenges in reduced or zero gravity space enviromnents. In this paper, an ejected spray cooling system for space closed-loop application was proposed and the negative pressure in the ejected condenser chamber was applied to sucking the two-phase mixture from the spray chamber. Its ground experimental setup was built and exper- imental investigations on the smooth circle heat surface with a diameter of 5 mm were conducted with distilled water as the coolant spraying from a nozzle of 0.51 mm orifice diameter at the inlet temperatures of 69.2 ℃ and 78.2 ℃ under the conditions of heat flux ranging from 69.76 W/cm2 to 311.45 W/cm2, volume flow through the spray nozzle varying from 11,22 L:h to 15.76 L·h. Work performance of the spray nozzle and heat transfer performance of the spray cooling system were analyzed; results show that this ejected spray cooling system has a good heat transfer performance and provides valid foundation for space closed-loop application in the near future.展开更多
In recent years,the problem of heat dissipation in airborne directed energy weapons has attracted considerable research interest.Spray cooling can be applied to cool airborne directed energy weapons,owing to its sever...In recent years,the problem of heat dissipation in airborne directed energy weapons has attracted considerable research interest.Spray cooling can be applied to cool airborne directed energy weapons,owing to its several advantages such as a large heat transfer coefficient,absence of boiling hysteresis and uniform surface temperature.To examine the potential of an airborne spray cooling system,the typical high heat flux dissipation methods were compared,and the state of the art research on spray cooling was reviewed.This review was focused on studies related to the spray cooling hydrodynamic mechanism,experimental studies of closed loop spray cooling,numerical simulation studies about spray cooling and the identification of the factors influencing spray cooling systems,and investigations related to the multiple nozzle spray cooling technology and heat transfer correlation predictions.Overall,there is a need for further research to investigate the failure phenomenon after the critical state,matching operation of the total system and microscopic characteristics of airborne specific parameters.展开更多
High power electronics units generate high-density heat flux,which poses a significant threat to the reliability of these devices.The vapor chamber(VC)has a very high heat transfer rate and has a wide range of applica...High power electronics units generate high-density heat flux,which poses a significant threat to the reliability of these devices.The vapor chamber(VC)has a very high heat transfer rate and has a wide range of applications in the heat dissipation of electronic products.VCs with sintered copper powder wicks sized as irregular shape copper powder 50μm(I-50μm),I-75μm,I-110μm,I-150μm were studied in this paper.The effect of liquid filling ratio was discussed.The results indicated that the thermal resistance of all VCs decreased with the increase of heating power.The capillary performance of wick was the dominant factor for the heat transfer performance of VCs with different kinds of wick.A capillary performance factor was proposed to evaluate the capillary performance of VCs.The capillary performance factor of VC with the wick of I-75μm was much higher than that of the other types of VC in this study.The heat source surface temperature of VCs could be affected by filling ratio and wick structure.But,it should be insensitive to the filling ratio when a better capillary performance factor was obtained.With the same heating area and similar structure,the maximum heat flux density of the VC would decrease as the height of vapor cavity decreased.展开更多
The intermediate fluid vaporizer(IFV)is a typical vaporizer of liquefied natural gas(LNG),which in general consists of three shell-and-tube heat exchangers(an evaporator,a condenser,and a thermolator).LNG is heated by...The intermediate fluid vaporizer(IFV)is a typical vaporizer of liquefied natural gas(LNG),which in general consists of three shell-and-tube heat exchangers(an evaporator,a condenser,and a thermolator).LNG is heated by seawater and the intermediate fluid in these heat exchangers.A one-dimensional heat transfer model for IFV is established in this paper in order to investigate the influences of structure and operation parameters on the heat transfer performance.In the rated condition,it is suggested to reduce tube diameters appropriately to get a large total heat transfer coefficient and increase the tube number to ensure the sufficient heat transfer area.According to simulation results,although the IFV capacity is much larger than the simplified-IFV(SIFV)capacity,the mode of SIFV could be recommended in some low-load cases as well.In some cases at high loads exceeding the capacity of a single IFV,it is better to add an AAV or an SCV operating to the IFV than just to increase the mass flow rate of seawater in the IFV in LNG receiving terminals.展开更多
基金support by the Scientific Research Start-up Funds for introducing Talent in the Sichuan University (20822041C4014)National Science and Technology Major Project of China (2017-I-0004-0004)。
文摘The flow and heat transfer characteristics of n-decane in the sub-millimeter spiral tube(SMST) at supercritical pressure(p = 3 MPa) are studied by the RNG k-ε numerical model in this paper. The effects of various Reynolds numbers(Re) and structural parameters pitch(s) and spiral diameter(D) are analyzed.Results indicate that the average Nusselt numberNu and friction factorNu increase with an increase in Re, and decrease with an increase in D/d(tube diameter). In terms of the structural parameter s/d, it is found that as s/d increases, the Nu first increase, and then decrease. and the critical structural parameter is s/d = 4. Compared with the straight tube, the SMST can improve Nu by 34.8% at best, while it can improve Nu by 102.1% at most. In addition, a comprehensive heat transfer coefficient is applied to analyze the thermodynamic properties of SMST. With the optimal structural parameters of D/d = 6 and s/d = 4, the comprehensive heat transfer factor of supercritical pressure hydrocarbon fuel in the SMST can reach 1.074. At last, correlations of the average Nusselt number and friction factor are developed to predict the flow and heat transfer of n-decane at supercritical pressure.
基金Supported by the National Natural Science Foundation of China(Grant Nos.51975135 and 52005422)Guangzhou Science and Technology Project(Grant No.201707010429)Special Innovation Projects of Universities in Guangdong Province(Grant No.2018GKTSCX085).
文摘With the advent of the 5G era,the design of electronic equipment is developing towards thinness,intelligence and multi-function,which requires higher cooling performance of the equipment.Micro-channel heat sink is promising for the heat dissipation of super-thin electronic equipment.In this study,thermal resistance theoretical model of the micro-channel heat sink was first established.Then,fabrication process of the micro-channel heat sink was introduced.Subsequently,heat transfer performance of the fabricated micro-channel heat sink was tested through the developed testing platform.Results show that the developed micro-channel heat sink has more superior heat dissipation performance over conventional metal solid heat sink and it is well suited for high power LEDs application.Moreover,the micro-channel structures in the heat sink were optimized by orthogonal test.Based on the orthogonal optimization,heat dissipation performance of the micro-channel radiator was further improved.
基金supported by the National MCF Energy R&D Program(No.2018YFE0312300)the National Key Research and Development Program of China(No.2017YFA0402500)the Science Foundation of the Institute of Plasma Physics,Chinese Academy of Sciences(No.Y45ETY2302)。
文摘The divertor target components for the Chinese fusion engineering test reactor(CFETR)and the future experimental advanced superconducting tokamak(EAST)need to remove a heat flux of up to20 MW m-2.In view of such a high heat flux removal requirement,this study proposes a conceptual design for a flat-tile divertor target based on explosive welding and brazing technology.Rectangular water-cooled channels with a special thermal transfer structure(TTS)are designed in the heat sink to improve the flat-tile divertor target’s heat transfer performance(HTP).The parametric design and optimization methods are applied to study the influence of the TTS variation parameters,including height(H),width(W*),thickness(T),and spacing(L),on the HTP.The research results show that the flat-tile divertor target’s HTP is sensitive to the TTS parameter changes,and the sensitivity is T>L>W*>H.The HTP first increases and then decreases with the increase of T,L,and W*and gradually increases with the increase of H.The optimal design parameters are as follows:H=5.5 mm,W*=25.8 mm,T=2.2 mm,and L=9.7 mm.The HTP of the optimized flat-tile divertor target at different flow speeds and tungsten tile thicknesses is studied using the numerical simulation method.A flat-tile divertor mock-up is developed according to the optimized parameters.In addition,high heat flux(HHF)tests are performed on an electron beam facility to further investigate the mock-up HTP.The numerical simulation calculation results show that the optimized flat-tile divertor target has great potential for handling the steady-state heat load of 20 MW m-2under the tungsten tile thickness<5 mm and the flow speed7 m s^(-1).The heat transfer efficiency of the flat-tile divertor target with rectangular cooling channels improves by13%and30%compared to that of the flat-tile divertor target with circular cooling channels and the ITER-like monoblock,respectively.The HHF tests indicate that the flat-tile divertor mock-up can successfully withstand 1000 cycles of20 MW m-2of heat load without visible deformation,damage,and HTP degradation.The surface temperature of the flat-tile divertor mock-up at the 1000th cycle is only930℃.The flat-tile divertor target’s HTP is greatly improved by the parametric design and optimization method,and is better than the ITER-like monoblock and the flat-tile mock-up for the WEST divertor.This conceptual design is currently being applied to the engineering design of the CFETR and EAST flat-tile divertors.
文摘In this paper,we take the mid-temperature gravity heat pipe exchanger as the research object,simulate the fluid flow field,temperature field and the working state of heat pipe in the heat exchanger by Fluent software.The effects of different operating parameters and fin parameters on the heat transfer performance of heat exchangers are studied.The results show that the heat transfer performance of the mid-temperature gravity heat pipe exchanger is the best when the fin spacing is between 5 mm and 6 mm,the height of the heat pipe is between 12 mm and 13 mm,and the inlet velocity of the fluid is between 2.5 m/s to 3 m/s.
文摘Considering utilization of the original chromium-bronze material, two processing techniques including hydraulic expansion and high temperature vacuum welding were proposed for the optimization of heat-sink structure in EAST. The heat transfer performance of heat-sink with or without cooling tube was calculated and different types of connection between tube and heat-sink were compared by conducting a special test. It is shown from numerical analysis that the diameter of heat-sink channel can be reduced from 12 mm to 10 mm. Compared with the original sample, the thermal contact resistance between tube and heat-sink for welding sample can reduce the heat transfer performance by 10%, while by 20% for the hydraulic expansion sample. However, the welding technique is more complicated and expensive than hydraulic expansion technique. Both the processing technique and the heat transfer performance of heat-sink prototype should be further considered for the optimization of heat-sink structure in EAST.
文摘In order to improve the performance of vehicle radiators, a two-dimensional heat transfer steady-state model of the radiator was set up. The influence of the structural parameters (axial ratio) of the heat exchange tube on the windward side on the heat transfer performance of the radiator was studied. With the increase of the axial ratio of the heat exchange tube on the windward side, the heat exchange capacity of the heat exchange tube surface slightly decreases. The heat exchange area increases significantly, which increases the total heat exchange of the radiator and improves the heat transfer performance of the radiator. When the axial ratio increases from 1.0 to 2.0, the average surface heat transfer capacity decreases from 5664.16</span><span style="font-family:""> </span><span style="font-family:Verdana;">W/m<sup>2</sup> to 5623.57</span><span style="font-family:""> </span><span style="font-family:Verdana;">W/m<sup>2</sup>.
基金the financial support from the National Natural Science Foundation of China (No. 50674096)PetroChina Scientific & Technological Risk Innovation Project (No. 060511-2-1)
文摘Compared with a conventional single section two-phase closed thermosyphon (TPCT) wellbore, a two-section TPCT wellbore has better heat transfer performance, which may improve the temperature distribution of fluid in wellbores, increase the temperature of fluid in wellheads and even more effectively reduce the failure rate of conventional TPCT wellbores. Heat transfer performance of two-section TPCT wellbores is affected by working medium, combination mode and oil flow rate. Different working media are introduced into the upper and lower TPCTs, which may achieve a better match between the working medium and the temperature field in the wellbores. Interdependence exists between the combination mode and the flow rate of the oil, which affects the heat transfer performance of a two-section TPCT wellbore. The experimental results show that a two-section TPCT wellbore, with equal upper and lower TPCTs respectively filled with Freon and methanol, has the best heat transfer performance when the oil flow rate is 200 L/h.
基金This work was supported by the Natural Science Foundation of China,Grant#11947012Anhui Provincial Natural Science Foundation,Grant#1908085MA08+1 种基金Open fund from State Key Laboratory of Aero-dynamics,Grant#PA2018GKSK0046Fundamental Research Funds for the Central Universities,Grant#JZ2019HGTA0035.
文摘In the present work,a numerical investigation on the coaxial shallow borehole heat exchanger based on Com-putational Fluid Dynamics(CFD)technique in Hefei city of China has been performed.The effects of design parameters,including inlet flow rate,inlet fluid temperature,inner pipe material and outer pipe diameter,on the heat transfer performance were systematically studied.Besides,the thermal behavior along the pipe has been carefully examined with focus on the thermal short-circuiting phenomena.When the fluid inlet velocity is less than the critical value,the turbulence intensity increases and the Nusselt number increases with the inlet flow rate increasing.However,there is sufficient time for heat transfer between the fluid in inner pipe and outer pipe because of low flow rates,leading to large heat loss,i.e.,thermal short-circuiting phenomenon.It is found that with the inlet flow rate increasing,the heat transfer increases first and then decreases,and the rate of reduction slows down gradually.When the inlet flow rate increases,the pumping power undergoes exponential growth.As the inlet temperature increasing,the heat transfer decreases almost linearly.Moreover,when the soil temperature at the top of the casing is lower than that of the fluid in the casing,heat is transferred from the fluid in the casing to the soil,and the heat loss increases with the increase of the inlet fluid temperature.The material of inner pipe with high heat conductivity would result in large heat loss under the influence of thermal short-circuiting.The heat load increases while the pumping power required decreases with the increasing of outer pipe diameter.This study is very beneficial for the coaxial shallow borehole exchanger designs and energy conservation of buildings.
基金The financial supports for this research,from the National Basic Research Program of China(Grant No.2015CB251503)Central University Fundation of China(Grant No.JB2018130)。
文摘The winds will greatly weaken the cooling performance of indirect dry cooling system with twin towers.The exterior windbreakers are recommended to restrain the wind adverse effects in this paper.The macro heat exchanger model was adopted to simulate the heat exchange between circulating water and ambient air.The performances of natural draft dry cooling system(NDDCS)with and without exterior windbreakers were numerically studied.The pressure,velocity and temperature distribution of cooling air in wind angles of 0°,45°and 90°was obtained and presented.The results show that in all wind directions,the performances for lateral sector of towers with windbreakers are significantly improved,but the low-pressure zone appears unexpectedly for the rear sectors,which reduces the air flow rate.The cooling performances of the twin towers with or without windbreakers decrease at first but then recover with the wind velocity increasing.Besides,the optimal flow and heat transfer performances appear in the wind angle of 0°.The cooling performances can be significantly improved in all three wind directions due to windbreaker configuration.
基金supported by the National Natural Science Foundation of China (51676163)the Fundamental Research Fund of Shenzhen City of China(JCYJ20170306155153048)+3 种基金the National 111 Project under Grant No. B18041the China Scholarship Council (CSC)provided by the Swedish National Infrastructure for Computing (SNIC) at LUNARCpartially funded by the Swedish Research Council
文摘This paper presents three-dimensional numerical simulations with the established realizable k-εmodel to clarify the underlying and interacting mechanisms between the film cooling and the internal cooling.On the one hand,the effects of three different internal cooling channels,i.e.,smooth channel,continuous ribbed channel,and truncated ribbed channel,on the film cooling effectiveness and the discharge coefficients are investigated.On the other hand,the influences of three different film cooling holes,i.e.,cylindrical hole,two elliptical holes and two circular-to-elliptical holes,on the heat transfer performances and pressure loss of the internal cooling channel are revealed.Especially,the suction effects of the film cooling holes are analyzed through setting up baselines with only internal cooling channels.Results show that the placement of ribs in the internal channel has different influences on the film cooling effectiveness with respect to different hole shapes depending on the blowing ratio.The discharge coefficient of the film hole can be improved by introducing ribs to the internal channel.Suction of film hole is helpful for enhancing the heat transfer performance and reducing the pressure loss of the internal channel.Besides,ribs instead of the suction effect of film hole play a major role to enhance the heat transfer performance in the internal cooling channel.
基金supported by the National Natural Science Foundation of China(No.50506003)
文摘Spray cooling has proved its superior heat transfer performance in removing high heat flux for ground applications. However, the dissipation of vapor liquid mixture from the heat sur- face and the closed-loop circulation of the coolant are two challenges in reduced or zero gravity space enviromnents. In this paper, an ejected spray cooling system for space closed-loop application was proposed and the negative pressure in the ejected condenser chamber was applied to sucking the two-phase mixture from the spray chamber. Its ground experimental setup was built and exper- imental investigations on the smooth circle heat surface with a diameter of 5 mm were conducted with distilled water as the coolant spraying from a nozzle of 0.51 mm orifice diameter at the inlet temperatures of 69.2 ℃ and 78.2 ℃ under the conditions of heat flux ranging from 69.76 W/cm2 to 311.45 W/cm2, volume flow through the spray nozzle varying from 11,22 L:h to 15.76 L·h. Work performance of the spray nozzle and heat transfer performance of the spray cooling system were analyzed; results show that this ejected spray cooling system has a good heat transfer performance and provides valid foundation for space closed-loop application in the near future.
基金supported by the National Natural Science Foundation of China(Grant No.51806096)China Postdoctoral Science Foundation(No.2019M661812)+1 种基金Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.18KJB560007)the Research Fund of Key Laboratory of Aircraft Environment Control and Life Support,MIIT,Nanjing University of Aeronautics and Astronautics(Grant No.KLAECLS-E-201902)。
文摘In recent years,the problem of heat dissipation in airborne directed energy weapons has attracted considerable research interest.Spray cooling can be applied to cool airborne directed energy weapons,owing to its several advantages such as a large heat transfer coefficient,absence of boiling hysteresis and uniform surface temperature.To examine the potential of an airborne spray cooling system,the typical high heat flux dissipation methods were compared,and the state of the art research on spray cooling was reviewed.This review was focused on studies related to the spray cooling hydrodynamic mechanism,experimental studies of closed loop spray cooling,numerical simulation studies about spray cooling and the identification of the factors influencing spray cooling systems,and investigations related to the multiple nozzle spray cooling technology and heat transfer correlation predictions.Overall,there is a need for further research to investigate the failure phenomenon after the critical state,matching operation of the total system and microscopic characteristics of airborne specific parameters.
基金supported by Fundamental Research Funds for the Central Universities(2018JBZ108)National Natural Science Foundation of China(No.51776015).
文摘High power electronics units generate high-density heat flux,which poses a significant threat to the reliability of these devices.The vapor chamber(VC)has a very high heat transfer rate and has a wide range of applications in the heat dissipation of electronic products.VCs with sintered copper powder wicks sized as irregular shape copper powder 50μm(I-50μm),I-75μm,I-110μm,I-150μm were studied in this paper.The effect of liquid filling ratio was discussed.The results indicated that the thermal resistance of all VCs decreased with the increase of heating power.The capillary performance of wick was the dominant factor for the heat transfer performance of VCs with different kinds of wick.A capillary performance factor was proposed to evaluate the capillary performance of VCs.The capillary performance factor of VC with the wick of I-75μm was much higher than that of the other types of VC in this study.The heat source surface temperature of VCs could be affected by filling ratio and wick structure.But,it should be insensitive to the filling ratio when a better capillary performance factor was obtained.With the same heating area and similar structure,the maximum heat flux density of the VC would decrease as the height of vapor cavity decreased.
文摘The intermediate fluid vaporizer(IFV)is a typical vaporizer of liquefied natural gas(LNG),which in general consists of three shell-and-tube heat exchangers(an evaporator,a condenser,and a thermolator).LNG is heated by seawater and the intermediate fluid in these heat exchangers.A one-dimensional heat transfer model for IFV is established in this paper in order to investigate the influences of structure and operation parameters on the heat transfer performance.In the rated condition,it is suggested to reduce tube diameters appropriately to get a large total heat transfer coefficient and increase the tube number to ensure the sufficient heat transfer area.According to simulation results,although the IFV capacity is much larger than the simplified-IFV(SIFV)capacity,the mode of SIFV could be recommended in some low-load cases as well.In some cases at high loads exceeding the capacity of a single IFV,it is better to add an AAV or an SCV operating to the IFV than just to increase the mass flow rate of seawater in the IFV in LNG receiving terminals.