An investigation of the decoupled thermal–hydraulic analysis of a separated heat pipe spent fuel pool passive cooling system(SFS)is essential for practical engineering applications.Based on the principles of thermal ...An investigation of the decoupled thermal–hydraulic analysis of a separated heat pipe spent fuel pool passive cooling system(SFS)is essential for practical engineering applications.Based on the principles of thermal and mass balance,this study decoupled the heat transfer processes in the SFS.In accordance with the decoupling conditions,we modeled the spent fuel pool of the CAP1400 pressurized water reactor in Weihai and used computational fluid dynamics to explore the heat dissipation capacity of the SFS under different air temperatures and wind speeds.The results show that the air-cooled separated heat pipe radiator achieved optimal performance at an air temperature of 10℃ or wind speed of 8 m/s.Fitted equations for the equivalent thermal conductivity of the separated heat pipes with the wind speed and air temperature we obtained according to the thermal resistance network model.This study is instructive for the actual operation of an SFS.展开更多
This research tests the effect of introducing turbulators of a new type into a circular tube heat exchanger under a constant and uniform longitudinal heatflux condition.A 45 mm diameter copper tube with a length of 1,3...This research tests the effect of introducing turbulators of a new type into a circular tube heat exchanger under a constant and uniform longitudinal heatflux condition.A 45 mm diameter copper tube with a length of 1,350 mm is utilized with a solid disk being inserted inside the tube,which consists of three sections,each one containing two slots.The slot is cut at a 45 degree angle toward the inner tube surface,which results in diverging theflow toward the inner hot tube surface in order to enhance the heat transfer process.Air is considered as the workingfluid with Prandtl number 0.71.The Reynolds number spans the interval from 6,000–13,500,which indicates that the consideredflow is turbulent.The heat exchanger performance is studied and analyzed in terms of average Nusselt number.The experimental results show that the Nusselt number value is directly proportional to the increase of the Reynolds number,and the number of turbulators inserts.With the use of three novel turbulators,the heat transfer was about 3.15 times higher than that in the smooth tube and the friction factor was about 1.11.展开更多
This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat...This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.展开更多
This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat...This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.展开更多
Lithium heat pipes have broad applications in heat pipe cooling reactors and hypersonic vehicles owing to their ultra-high working temperature.In particular,when the length of the lithium heat pipe is ultra-long,the f...Lithium heat pipes have broad applications in heat pipe cooling reactors and hypersonic vehicles owing to their ultra-high working temperature.In particular,when the length of the lithium heat pipe is ultra-long,the flow and heat transfer characteristics are more complex.In this study,an improved lumped parameter model that considers the Marangoni effect,bending effect,and different vapor flow patterns and Mach numbers was developed.Thereafter,the proposed model was verified using the University of New Mexico’s Heat Pipe and HTPIPE models.Finally,the verified model was applied to simulate the steady-state operation of an ultra-long lithium heat pipe in a Heat PipeSegmented Thermoelectric Module Converters space reactor.Based on the results:(1)Vapor thermal resistance was dominant at low heating power and decreased with increasing heating power.The vapor flow inside the heat pipe developed from the laminar to the turbulent phase,whereas the liquid phase in the heat pipe was always laminar.(2)The vapor pressure drop caused by bending was approximately 22–23%of the total,and the bending effect on the liquid pressure drop could be ignored.(3)The Marangoni effect reduced the capillary limit by hindering the liquid reflux,especially at low vapor temperatures.Without considering the Marangoni effect,the capillary limit of the lithium heat pipe was overestimated by 9%when the vapor temperature was 1400 K.(4)The total thermal resistance of the heat pipe significantly increased with increasing adiabatic length when the vapor temperature was low.Further,the wick dryness increased with increasing adiabatic length at any vapor temperature.Such findings improve on current knowledge for the optimal design and safety analysis of a heat pipe reactor,which adopts ultra-long lithium heat pipes.展开更多
Satellite's thermal control subsystem (TCS) has to maintain components and structure within their specified temperature limits during satellite service life. TCS designers have to face the challenge of reducing bot...Satellite's thermal control subsystem (TCS) has to maintain components and structure within their specified temperature limits during satellite service life. TCS designers have to face the challenge of reducing both the weight of the system and required heater power while keeping components temperature within their design range. For a space based heat pipe radiator system, several researchers have published different approaches to reach such goal. This paper presents a thermal design and optimization of a heat pipe radiator applied to a practical engineering design application. For this study, a prospective communication satellite payload panel with applied passive thermal control techniques was considered. The thermal passive techniques used in this design mainly include multilayer insulation (MLI) blankets, optical solar reflectors (OSR), selected thermal coatings, interface fillers and constant conductance heat pipes. The heat pipe network is comprised of some heat pipes embedded in the panel and some mounted on inner surface of the panel. Embedded heat pipes are placed under high heat dissipation equipments and their size is fixed; minimum weight of the radiator is achieved by a minimum weight of the mounted heat pipes. Hence, size of the mounted heat pipes is optimized. A thermal model was built and parameterized for transient thermal analysis and optimization. Temperature requirements of components in both worst case conditions (Hot case and cold case) were satisfied under optimal sizing of mounted heat pipes.展开更多
Due to the heat pipes’ transient conduction,phase change and fluid dynamics during cooling/heating with high frequency charging/discharging of batteries,it is crucial to investigate in depth the experimental dynamic ...Due to the heat pipes’ transient conduction,phase change and fluid dynamics during cooling/heating with high frequency charging/discharging of batteries,it is crucial to investigate in depth the experimental dynamic thermal characteristics in such complex heat transfer processes for more accurate thermal analysis and design of a BTMS. In this paper,the use of ultra?thin micro heat pipe(UMHP) for thermal management of a lithium?ion battery pack in EVs is explored by experiments to reveal the cooling/heating characteristics of the UMHP pack. The cooling performance is evaluated under di erent constant discharging and transient heat inputs conditions. And the heating e ciency is assessed under several sub?zero temperatures through heating films with/without UMHPs. Results show that the pro?posed UMHP BTMS with forced convection can keep the maximum temperature of the pack below 40 °C under 1 ~ 3 C discharging,and e ectively reduced the instant temperature increases and minimize the temperature fluctuation of the pack during transient federal urban driving schedule(FUDS) road conditions. Experimental data also indicate that heating films stuck on the fins of UMHPs brought about adequate high heating e ciency comparing with that stuck on the surface of cells under the same heating power,but has more convenient maintenance and less cost for the BTMS. The experimental dynamic temperature characteristics of UMHP which is found to be a high?e cient and low?energy consumption cooling/heating method for BTMSs,can be performed to guide thermal analysis and optimiza?tion of heat pipe BTMSs.展开更多
The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no...The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no other better method to solve this problem. A new method by heating the heat pipe is proposed to eliminate the collapse during the flattening process. The effectiveness of the proposed method is investigated through a theoretical model, a finite element(FE) analysis, and experimental method. Firstly, A theoretical model based on a deformation model of six plastic hinges and the Antoine equation of the working fluid is established to analyze the collapse of thin walls at different temperatures. Then, the FE simulation and experiments of flattening process at different temperatures are carried out and compared with theoretical model. Finally, the FE model is followed to study the loads of the plates at different temperatures and heights of flattened heat pipes. The results of the theoretical model conform to those of the FE simulation and experiments in the flattened zone. The collapse occurs at room temperature. As the temperature increases, the collapse decreases and finally disappears at approximately 130 ℃ for various heights of flattened heat pipes. The loads of the moving plate increase as the temperature increases. Thus, the reasonable temperature for eliminating the collapse and reducing the load is approximately 130℃. The advantage of the proposed method is that the collapse is reduced or eliminated by means of the thermal deformation characteristic of heat pipe itself instead of by external support. As a result, the heat transfer efficiency of heat pipe is raised.展开更多
A suitable model for high-temperature heat pipe startup is a prerequisite to realizing the numerical simula-tion for the heat pipe cooled reactor startup from the cold state.It is required that this model not only des...A suitable model for high-temperature heat pipe startup is a prerequisite to realizing the numerical simula-tion for the heat pipe cooled reactor startup from the cold state.It is required that this model not only describes the transient behavior during the startup period,but also reduces the computing resources of the heat pipe cooled reactor simulation in the simplest way.In this study,a simplified model that integrates the two-zone and network models is proposed.In this model,vapor flow in the vapor space,evaporation,and condensation in the vapor–liquid interface are decoupled with heat conduction to achieve a fast calculation of the transient characteristics of the heat pipe.An experimental system for a high-temperature heat pipe was developed to validate the proposed model.A potassium heat pipe was utilized as the experimental material.Startup experiments were performed with differ-ent heating powers.Compared with the experimental results,the accuracy of the proposed model was verified.Moreover,the proposed model can predict the vapor flow,pressure drop,and temperature drop in the vapor space.As indicated by the analysis results,the essential requirements for successful startup are also determined.The heat pipe cannot achieve a successful startup until the heating power satisfies these requirements.All the discussions indicate the capability of the proposed model for the simulation of a high-temperature heat pipe startup from the frozen state;hence,can act as a basic tool for the heat pipe cooled reactor simulation.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
To study the heat and mass transfer characteristics of alkali metals in a combined porous wick in high-temperature heat pipes,a three-dimensional(3-D)numerical model is constructed by using the finite volume method,Da...To study the heat and mass transfer characteristics of alkali metals in a combined porous wick in high-temperature heat pipes,a three-dimensional(3-D)numerical model is constructed by using the finite volume method,Darcy’s theory,and the theory of local thermal equilibrium.The research finds that the pressure drop of fluids flowing through a combined porous wick exhibits an increasing trend with increasing flow velocity at the inlet and with decreasing permeability of the porous media;a combined porous wick of lower porosity and permeability and larger fluid velocity at the inlet is found to have a less uniformly distributed fluid velocity;the different temperatures of the fluid at the inlet mainly influence the inlet section of the computational model,while having negligible effect thereon in the axial direction(this embodies the thermal homogeneity of such heat pipes).The result reveals that the temperature change in fluids at the inlet does not significantly affect the overall temperature distribution in a combined wick.展开更多
Sealing quality strongly affects heat pipe performance, but few studies focus on the process of heat pipe sealing. Cold welding sealing technology based on a stamping process is applied for heat pipe sealing. The bond...Sealing quality strongly affects heat pipe performance, but few studies focus on the process of heat pipe sealing. Cold welding sealing technology based on a stamping process is applied for heat pipe sealing. The bonding mechanism of the cold welding sealing process (CWSP) is investigated and compared with the experimental results obtained from the bonding interface analysis. An orthogonal experiment is conducted to observe the effects of various parameters, including the sealing gap, sealing length, sealing diameter, and sealing velocity on bonding strength. A method with the utilization of saturated vapor pressure inside a copper tube is proposed to evaluate bonding strength. A corresponding finite element model is developed to investigate the effects of sealing gap and sealing velocity on plastic deformation during the cold welding process. Effects of various parameters on the bonding strength are determined and it is found that the sealing gap is the most critical factor and that the sealing velocity contributes the least effect. The best parameter combination (AIB3CID3, with a 0.5 mm sealing gap, 6 mm sealing length, 3.8 mm sealing diameter, and 50 mm/s sealing velocity) is derived within the experimental parameters. Plastic deformation results derived from the finite element model are consistent with those from the experiment. The instruction for the CWSP of heat pipes and the design of sealing dies of heat pipes are provided.展开更多
Computer chip is always accompanied by the increase of heat dissipation and miniaturization. The miniature heat pipes are widely used in notebook computer to resolve the heat dissipation problems. Maximum heat removed...Computer chip is always accompanied by the increase of heat dissipation and miniaturization. The miniature heat pipes are widely used in notebook computer to resolve the heat dissipation problems. Maximum heat removed model of miniature heat pipes building by grey model is presented. In order to know the foundation for modeling, the smooth grade of error examination is inquired and the accuracy of grey relational grade is verified. The model can be used to select a suitable heat pipes to solve electric heat problems in the future. Final results show that the grey model only needs four experiment data and its error value is less than 10%, further, it is better than computational fluid dynamics (CFD) model.展开更多
The pulsating heat pipe is a very promising heat dissipation device to address the challenge of higher heat-flux electronic chips,as it is characterised by excellent heat transfer ability and flexibility for miniaturi...The pulsating heat pipe is a very promising heat dissipation device to address the challenge of higher heat-flux electronic chips,as it is characterised by excellent heat transfer ability and flexibility for miniaturisation.To boost the application of PHP,reliable heat transfer performance evaluationmodels are especially important.In this paper,a heat transfer correlation was firstly proposed for closed PHP with various working fluids(water,ethanol,methanol,R123,acetone)based on collected experimental data.Dimensional analysis was used to group the parameters.It was shown that the average absolute deviation(AAD)and correlation coefficient(r)of the correlation were 40.67%and 0.7556,respectively.For 95%of the data,the prediction of thermal resistance and the temperature difference between evaporation and condensation section fell within 1.13K/Wand 40.76K,respectively.Meanwhile,an artificial neural networkmodelwas also proposed.The ANN model showed a better prediction accuracy with a mean square error(MSE)and correlation coefficient(r)of 7.88e-7 and 0.9821,respectively.展开更多
This experimental study is performed to investigate heat transfer performance of a multi-heat pipe cooling device in the condition of different filling ratios (40%, 60%, 80% and 100%) and different constant heat fluxe...This experimental study is performed to investigate heat transfer performance of a multi-heat pipe cooling device in the condition of different filling ratios (40%, 60%, 80% and 100%) and different constant heat fluxes (10 - 30 W). Here, pure water (distilled water) and graphene oxide (GO)/water nanofluids are employed respectively as working fluid. GO/water nanofluids were synthesized by the modified Hummers method with 0.05%, 0.10%, 0.15%, and 0.20% volume concentrations. Multi-heat pipe is fabricated from copper;the heating and cooling sections are the same size and both are connected by four circular parallel tubes. Temperature fields and thermal resistance are measured for different filling ratio, heat fluxes and volume concentrations. The results indicated that the thermal performance of heat pipe increased with increasing the concentration of GO nanoparticles in the base fluid, while the maximum heat transfer enhancement was observed at 0.20% volume concentration. GO/water nanofluids showed lower thermal resistance compared to pure water;the optimal thermal resistance was obtained at 100% filling charge ratio with 0.20% volume concentration. Studies were also demonstrated that heat transfer coefficient of the heat pipe significantly increases with increasing the input heat flux and GO nanoparticles concentration.展开更多
In order to investigate the mechanism of the temperature oscillation in loop heat pipes,this paper investigated the movement of the phase interface as the changed input power by a mass-spring-damper model.The model wa...In order to investigate the mechanism of the temperature oscillation in loop heat pipes,this paper investigated the movement of the phase interface as the changed input power by a mass-spring-damper model.The model was solved with MATLAB and was used to explain the high-frequency and low-amplitude temperature oscillation.Temperature variation with the input power from 20 W to 75 W was investigated based on a LHP prototype in a literature.The model agreed well with the experimental data in the literature.The simulation results suggested that the movement of the liquid column was caused by the fluctuation of pressure difference applied on the liquid column and the stiffness coefficients of the vapor springs increasing with the input power.According to parameter analyses,the temperature oscillation at the outlet of the condenser can be weakened by increasing the mass of the liquid column and keeping the temperature at the outlet of the condenser steady.展开更多
A comparative numerical study has been conducted on the thermal performance of a heat pipe cooling system considering several influential factors such as the coolant flow rate,the coolant inlet temperature,and the inp...A comparative numerical study has been conducted on the thermal performance of a heat pipe cooling system considering several influential factors such as the coolant flow rate,the coolant inlet temperature,and the input power.A comparison between numerical data and results available in the literature has demonstrated that our numerical procedure could successfully predict the heat transfer performance of the considered heat pipe cooling system for a battery.Specific indicators such as temperature,heat flux,and pressure loss were extracted to describe the characteristics of such a system.On the basis of the distributions of the temperature ratio of the battery surface,together with the heat flux and the streamlines around the heat pipe condenser,we conclude that the low disturbance of the coolant is the cause of the temperature gradient along the fluid flow direction.展开更多
The building energy consumption is an important part among the total society energy consumption,in which the energy consumption for air conditioning occupies almost 70%.The energy consumption of the air conditioning s...The building energy consumption is an important part among the total society energy consumption,in which the energy consumption for air conditioning occupies almost 70%.The energy consumption of the air conditioning system for fresh air handling can be saved effectively when the exhaust air energy could be recovered to preheat or precool the fresh air.Considering the install locations requirements on field,the pump-driven heat pipes(PHP)were developed as heat recovery ventilators(HRVs)and used in an existing experiment building in Beijing Urban.The thermal performance of the PHP HRVs was tested in real operation time periods under winter running mode.Both the power and heat consumption of the modular air handling units with and without HRVs were monitored and obtained,as well as the hourly power and heat consumption.The energy savings of HRVs were analyzed.The results indicate that the PHP HRVs can work steadily and meet the energy recovery need well.The temperature effectiveness of the HRVs can be kept from 60%to 70%.The test total energy saving rate was 24.48%,and the average hourly heat consumption reduced by 28.54%.The daily energy consumption can be saved by 118 kWh,and the energy savings can reach to 9440 kWh for a whole winter.展开更多
The temperature control in electronic packaging is the key in numerous applications,to avoid overheating and hardware failure.Due to high capability of heat transfer,good temperature uniformity,and no power consumptio...The temperature control in electronic packaging is the key in numerous applications,to avoid overheating and hardware failure.Due to high capability of heat transfer,good temperature uniformity,and no power consumption,heat pipes can be widely used for heat dissipation of electronic components.This paper reports an experimental thermal analysis of different capillary structures for heat pipes.The wicks considered are metal screens,axial microgrooves,and sintered metal powder.The heat pipes are made of copper,a 200 mm length tube and a 9.45 mm external diameter.Working fluid used was distilled water.The devices are investigated in three positions:0,90,and 270°to the horizontal under powers of 5 up to 45 W.The results show that in horizontal(0°)and with the evaporator under the condenser(270°),the heat pipes showed similar results.Nevertheless,in the reverse condition(the position against the gravity with the evaporator above the condenser,90°),the heat pipe with sintered wick presented the best thermal performance,as it has the lowest thermal resistance and supported a higher power.Besides that,the sintered powder capillary structure demonstrates the most homogeneous thermal behavior for every position,making the most suitable for applications susceptible to diverse inclinations.展开更多
Multiple loop heat pipe is a high-functional thermal transport device. This work was conducted to confirm the working performance of Multiple loop heat pipe under thermal vacuum ambience with the working fluid ammonia...Multiple loop heat pipe is a high-functional thermal transport device. This work was conducted to confirm the working performance of Multiple loop heat pipe under thermal vacuum ambience with the working fluid ammonia. Asmall multiple loop heat pipe with two evaporators and two ra- diators was designed and fabricated. Then thermal vacuum test was conducted. The heaters were fasten on both evaporators, both radiators, both compensation chambers. In the case that both evaporators were heated, the multiple loop heat pipe can transport 120/120 W for 1.5 m, in the case that only one evaporator was heated, evaporator 1 can transport 80 W for 1.5 m, while eva- porator 2 can transport 120 W for 1.5 m. Two flow regulators were installed near the confluence of liquid line to prevent uncondensed vapor penetrating into returning liquid when the tempera- ture difference exists between two radiators. In the case that the heat load at both evaporators were 40/40 W and one radiator was heated, the flow regulator1 can tolerate the 160 W of heat load which was supplied to radiator1 while the flow regulator2 can tolerate the 100 W of heat load which was supplied to radiator2. To demonstrate the multiple loop heat pipe’s startup behavior at lowheat load, each of the compensation chamber was preheated to change the initial distribution of liquid and vapor in the evaporator and compensation chamber, in the result, each evaporator can start up at 5W through preheating.展开更多
文摘An investigation of the decoupled thermal–hydraulic analysis of a separated heat pipe spent fuel pool passive cooling system(SFS)is essential for practical engineering applications.Based on the principles of thermal and mass balance,this study decoupled the heat transfer processes in the SFS.In accordance with the decoupling conditions,we modeled the spent fuel pool of the CAP1400 pressurized water reactor in Weihai and used computational fluid dynamics to explore the heat dissipation capacity of the SFS under different air temperatures and wind speeds.The results show that the air-cooled separated heat pipe radiator achieved optimal performance at an air temperature of 10℃ or wind speed of 8 m/s.Fitted equations for the equivalent thermal conductivity of the separated heat pipes with the wind speed and air temperature we obtained according to the thermal resistance network model.This study is instructive for the actual operation of an SFS.
文摘This research tests the effect of introducing turbulators of a new type into a circular tube heat exchanger under a constant and uniform longitudinal heatflux condition.A 45 mm diameter copper tube with a length of 1,350 mm is utilized with a solid disk being inserted inside the tube,which consists of three sections,each one containing two slots.The slot is cut at a 45 degree angle toward the inner tube surface,which results in diverging theflow toward the inner hot tube surface in order to enhance the heat transfer process.Air is considered as the workingfluid with Prandtl number 0.71.The Reynolds number spans the interval from 6,000–13,500,which indicates that the consideredflow is turbulent.The heat exchanger performance is studied and analyzed in terms of average Nusselt number.The experimental results show that the Nusselt number value is directly proportional to the increase of the Reynolds number,and the number of turbulators inserts.With the use of three novel turbulators,the heat transfer was about 3.15 times higher than that in the smooth tube and the friction factor was about 1.11.
文摘This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.
文摘This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.
基金the CASHIPS Director’s Fund(No.YZJJ2021QN36)the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-KT-2019-1-0202).
文摘Lithium heat pipes have broad applications in heat pipe cooling reactors and hypersonic vehicles owing to their ultra-high working temperature.In particular,when the length of the lithium heat pipe is ultra-long,the flow and heat transfer characteristics are more complex.In this study,an improved lumped parameter model that considers the Marangoni effect,bending effect,and different vapor flow patterns and Mach numbers was developed.Thereafter,the proposed model was verified using the University of New Mexico’s Heat Pipe and HTPIPE models.Finally,the verified model was applied to simulate the steady-state operation of an ultra-long lithium heat pipe in a Heat PipeSegmented Thermoelectric Module Converters space reactor.Based on the results:(1)Vapor thermal resistance was dominant at low heating power and decreased with increasing heating power.The vapor flow inside the heat pipe developed from the laminar to the turbulent phase,whereas the liquid phase in the heat pipe was always laminar.(2)The vapor pressure drop caused by bending was approximately 22–23%of the total,and the bending effect on the liquid pressure drop could be ignored.(3)The Marangoni effect reduced the capillary limit by hindering the liquid reflux,especially at low vapor temperatures.Without considering the Marangoni effect,the capillary limit of the lithium heat pipe was overestimated by 9%when the vapor temperature was 1400 K.(4)The total thermal resistance of the heat pipe significantly increased with increasing adiabatic length when the vapor temperature was low.Further,the wick dryness increased with increasing adiabatic length at any vapor temperature.Such findings improve on current knowledge for the optimal design and safety analysis of a heat pipe reactor,which adopts ultra-long lithium heat pipes.
文摘Satellite's thermal control subsystem (TCS) has to maintain components and structure within their specified temperature limits during satellite service life. TCS designers have to face the challenge of reducing both the weight of the system and required heater power while keeping components temperature within their design range. For a space based heat pipe radiator system, several researchers have published different approaches to reach such goal. This paper presents a thermal design and optimization of a heat pipe radiator applied to a practical engineering design application. For this study, a prospective communication satellite payload panel with applied passive thermal control techniques was considered. The thermal passive techniques used in this design mainly include multilayer insulation (MLI) blankets, optical solar reflectors (OSR), selected thermal coatings, interface fillers and constant conductance heat pipes. The heat pipe network is comprised of some heat pipes embedded in the panel and some mounted on inner surface of the panel. Embedded heat pipes are placed under high heat dissipation equipments and their size is fixed; minimum weight of the radiator is achieved by a minimum weight of the mounted heat pipes. Hence, size of the mounted heat pipes is optimized. A thermal model was built and parameterized for transient thermal analysis and optimization. Temperature requirements of components in both worst case conditions (Hot case and cold case) were satisfied under optimal sizing of mounted heat pipes.
基金Supported by National Natural Science Foundation of China(Grant No.51775193)Guangdong Provincial Science and Technology Planning Project of China(Grant Nos.2014B010125001,2014B010106002,2016A050503021)Guangzhou Municipal Science and Technology Planning Project of China(Grant No.201707020045)
文摘Due to the heat pipes’ transient conduction,phase change and fluid dynamics during cooling/heating with high frequency charging/discharging of batteries,it is crucial to investigate in depth the experimental dynamic thermal characteristics in such complex heat transfer processes for more accurate thermal analysis and design of a BTMS. In this paper,the use of ultra?thin micro heat pipe(UMHP) for thermal management of a lithium?ion battery pack in EVs is explored by experiments to reveal the cooling/heating characteristics of the UMHP pack. The cooling performance is evaluated under di erent constant discharging and transient heat inputs conditions. And the heating e ciency is assessed under several sub?zero temperatures through heating films with/without UMHPs. Results show that the pro?posed UMHP BTMS with forced convection can keep the maximum temperature of the pack below 40 °C under 1 ~ 3 C discharging,and e ectively reduced the instant temperature increases and minimize the temperature fluctuation of the pack during transient federal urban driving schedule(FUDS) road conditions. Experimental data also indicate that heating films stuck on the fins of UMHPs brought about adequate high heating e ciency comparing with that stuck on the surface of cells under the same heating power,but has more convenient maintenance and less cost for the BTMS. The experimental dynamic temperature characteristics of UMHP which is found to be a high?e cient and low?energy consumption cooling/heating method for BTMSs,can be performed to guide thermal analysis and optimiza?tion of heat pipe BTMSs.
基金supported by National Natural Science Foundation of China(Grant Nos. 50975096, 51175186)Guangdong Provincial Natural Science Foundation of China(Grant No. S2011010002225)+1 种基金Guangdong Provincial Science and Technology Planning Project of China(GrantNos. 2010A080802009, 2010A011300022, 2011B040300020)Fundamental Research Funds for the Central Universities of China(GrantNo.2012ZZ0053)
文摘The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no other better method to solve this problem. A new method by heating the heat pipe is proposed to eliminate the collapse during the flattening process. The effectiveness of the proposed method is investigated through a theoretical model, a finite element(FE) analysis, and experimental method. Firstly, A theoretical model based on a deformation model of six plastic hinges and the Antoine equation of the working fluid is established to analyze the collapse of thin walls at different temperatures. Then, the FE simulation and experiments of flattening process at different temperatures are carried out and compared with theoretical model. Finally, the FE model is followed to study the loads of the plates at different temperatures and heights of flattened heat pipes. The results of the theoretical model conform to those of the FE simulation and experiments in the flattened zone. The collapse occurs at room temperature. As the temperature increases, the collapse decreases and finally disappears at approximately 130 ℃ for various heights of flattened heat pipes. The loads of the moving plate increase as the temperature increases. Thus, the reasonable temperature for eliminating the collapse and reducing the load is approximately 130℃. The advantage of the proposed method is that the collapse is reduced or eliminated by means of the thermal deformation characteristic of heat pipe itself instead of by external support. As a result, the heat transfer efficiency of heat pipe is raised.
基金This work was supported by the National Key Research and Development Project of China(No.2020YFB1901700)Science Challenge Project(No.TZ2018001)+1 种基金the National Natural Science Foundation of China(Nos.11775126 and 11775127)the Tsinghua University Initiative Scientific Research Program.
文摘A suitable model for high-temperature heat pipe startup is a prerequisite to realizing the numerical simula-tion for the heat pipe cooled reactor startup from the cold state.It is required that this model not only describes the transient behavior during the startup period,but also reduces the computing resources of the heat pipe cooled reactor simulation in the simplest way.In this study,a simplified model that integrates the two-zone and network models is proposed.In this model,vapor flow in the vapor space,evaporation,and condensation in the vapor–liquid interface are decoupled with heat conduction to achieve a fast calculation of the transient characteristics of the heat pipe.An experimental system for a high-temperature heat pipe was developed to validate the proposed model.A potassium heat pipe was utilized as the experimental material.Startup experiments were performed with differ-ent heating powers.Compared with the experimental results,the accuracy of the proposed model was verified.Moreover,the proposed model can predict the vapor flow,pressure drop,and temperature drop in the vapor space.As indicated by the analysis results,the essential requirements for successful startup are also determined.The heat pipe cannot achieve a successful startup until the heating power satisfies these requirements.All the discussions indicate the capability of the proposed model for the simulation of a high-temperature heat pipe startup from the frozen state;hence,can act as a basic tool for the heat pipe cooled reactor simulation.
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.
基金supported by the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20180177)the Science and Technology Foundation of Xuzhou,China(Grant No.KH17007)the Natural Science Foundation for Colleges and Universities of Jiangsu Province,China(Grant No.17KJB460015,No.18KJB460028).
文摘To study the heat and mass transfer characteristics of alkali metals in a combined porous wick in high-temperature heat pipes,a three-dimensional(3-D)numerical model is constructed by using the finite volume method,Darcy’s theory,and the theory of local thermal equilibrium.The research finds that the pressure drop of fluids flowing through a combined porous wick exhibits an increasing trend with increasing flow velocity at the inlet and with decreasing permeability of the porous media;a combined porous wick of lower porosity and permeability and larger fluid velocity at the inlet is found to have a less uniformly distributed fluid velocity;the different temperatures of the fluid at the inlet mainly influence the inlet section of the computational model,while having negligible effect thereon in the axial direction(this embodies the thermal homogeneity of such heat pipes).The result reveals that the temperature change in fluids at the inlet does not significantly affect the overall temperature distribution in a combined wick.
基金Supported by National Natural Science Foundation of China(Grant Nos.51175186,51675185)Guangdong Provincial Natural Science Foundation of China(Grant No.S2013020012757)EU project PIIF-GA-2012-332304(Grant No.ESR332304)
文摘Sealing quality strongly affects heat pipe performance, but few studies focus on the process of heat pipe sealing. Cold welding sealing technology based on a stamping process is applied for heat pipe sealing. The bonding mechanism of the cold welding sealing process (CWSP) is investigated and compared with the experimental results obtained from the bonding interface analysis. An orthogonal experiment is conducted to observe the effects of various parameters, including the sealing gap, sealing length, sealing diameter, and sealing velocity on bonding strength. A method with the utilization of saturated vapor pressure inside a copper tube is proposed to evaluate bonding strength. A corresponding finite element model is developed to investigate the effects of sealing gap and sealing velocity on plastic deformation during the cold welding process. Effects of various parameters on the bonding strength are determined and it is found that the sealing gap is the most critical factor and that the sealing velocity contributes the least effect. The best parameter combination (AIB3CID3, with a 0.5 mm sealing gap, 6 mm sealing length, 3.8 mm sealing diameter, and 50 mm/s sealing velocity) is derived within the experimental parameters. Plastic deformation results derived from the finite element model are consistent with those from the experiment. The instruction for the CWSP of heat pipes and the design of sealing dies of heat pipes are provided.
文摘Computer chip is always accompanied by the increase of heat dissipation and miniaturization. The miniature heat pipes are widely used in notebook computer to resolve the heat dissipation problems. Maximum heat removed model of miniature heat pipes building by grey model is presented. In order to know the foundation for modeling, the smooth grade of error examination is inquired and the accuracy of grey relational grade is verified. The model can be used to select a suitable heat pipes to solve electric heat problems in the future. Final results show that the grey model only needs four experiment data and its error value is less than 10%, further, it is better than computational fluid dynamics (CFD) model.
基金This work is funded by National Natural Science Foundation of China(No.51906216).
文摘The pulsating heat pipe is a very promising heat dissipation device to address the challenge of higher heat-flux electronic chips,as it is characterised by excellent heat transfer ability and flexibility for miniaturisation.To boost the application of PHP,reliable heat transfer performance evaluationmodels are especially important.In this paper,a heat transfer correlation was firstly proposed for closed PHP with various working fluids(water,ethanol,methanol,R123,acetone)based on collected experimental data.Dimensional analysis was used to group the parameters.It was shown that the average absolute deviation(AAD)and correlation coefficient(r)of the correlation were 40.67%and 0.7556,respectively.For 95%of the data,the prediction of thermal resistance and the temperature difference between evaporation and condensation section fell within 1.13K/Wand 40.76K,respectively.Meanwhile,an artificial neural networkmodelwas also proposed.The ANN model showed a better prediction accuracy with a mean square error(MSE)and correlation coefficient(r)of 7.88e-7 and 0.9821,respectively.
文摘This experimental study is performed to investigate heat transfer performance of a multi-heat pipe cooling device in the condition of different filling ratios (40%, 60%, 80% and 100%) and different constant heat fluxes (10 - 30 W). Here, pure water (distilled water) and graphene oxide (GO)/water nanofluids are employed respectively as working fluid. GO/water nanofluids were synthesized by the modified Hummers method with 0.05%, 0.10%, 0.15%, and 0.20% volume concentrations. Multi-heat pipe is fabricated from copper;the heating and cooling sections are the same size and both are connected by four circular parallel tubes. Temperature fields and thermal resistance are measured for different filling ratio, heat fluxes and volume concentrations. The results indicated that the thermal performance of heat pipe increased with increasing the concentration of GO nanoparticles in the base fluid, while the maximum heat transfer enhancement was observed at 0.20% volume concentration. GO/water nanofluids showed lower thermal resistance compared to pure water;the optimal thermal resistance was obtained at 100% filling charge ratio with 0.20% volume concentration. Studies were also demonstrated that heat transfer coefficient of the heat pipe significantly increases with increasing the input heat flux and GO nanoparticles concentration.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51276012)
文摘In order to investigate the mechanism of the temperature oscillation in loop heat pipes,this paper investigated the movement of the phase interface as the changed input power by a mass-spring-damper model.The model was solved with MATLAB and was used to explain the high-frequency and low-amplitude temperature oscillation.Temperature variation with the input power from 20 W to 75 W was investigated based on a LHP prototype in a literature.The model agreed well with the experimental data in the literature.The simulation results suggested that the movement of the liquid column was caused by the fluctuation of pressure difference applied on the liquid column and the stiffness coefficients of the vapor springs increasing with the input power.According to parameter analyses,the temperature oscillation at the outlet of the condenser can be weakened by increasing the mass of the liquid column and keeping the temperature at the outlet of the condenser steady.
基金by the Natural Science Foundation of Jiangsu Province(Grants No.BK20170317).
文摘A comparative numerical study has been conducted on the thermal performance of a heat pipe cooling system considering several influential factors such as the coolant flow rate,the coolant inlet temperature,and the input power.A comparison between numerical data and results available in the literature has demonstrated that our numerical procedure could successfully predict the heat transfer performance of the considered heat pipe cooling system for a battery.Specific indicators such as temperature,heat flux,and pressure loss were extracted to describe the characteristics of such a system.On the basis of the distributions of the temperature ratio of the battery surface,together with the heat flux and the streamlines around the heat pipe condenser,we conclude that the low disturbance of the coolant is the cause of the temperature gradient along the fluid flow direction.
基金supported by the Project of Science and Technology Program of Beijing Municipal Chao Yang District(CYSF2005,Zhun Li,http://www.bjchy.gov.cn/dynamic/notice/8a24fe83722fa7180172360a3f46044c.html).
文摘The building energy consumption is an important part among the total society energy consumption,in which the energy consumption for air conditioning occupies almost 70%.The energy consumption of the air conditioning system for fresh air handling can be saved effectively when the exhaust air energy could be recovered to preheat or precool the fresh air.Considering the install locations requirements on field,the pump-driven heat pipes(PHP)were developed as heat recovery ventilators(HRVs)and used in an existing experiment building in Beijing Urban.The thermal performance of the PHP HRVs was tested in real operation time periods under winter running mode.Both the power and heat consumption of the modular air handling units with and without HRVs were monitored and obtained,as well as the hourly power and heat consumption.The energy savings of HRVs were analyzed.The results indicate that the PHP HRVs can work steadily and meet the energy recovery need well.The temperature effectiveness of the HRVs can be kept from 60%to 70%.The test total energy saving rate was 24.48%,and the average hourly heat consumption reduced by 28.54%.The daily energy consumption can be saved by 118 kWh,and the energy savings can reach to 9440 kWh for a whole winter.
文摘The temperature control in electronic packaging is the key in numerous applications,to avoid overheating and hardware failure.Due to high capability of heat transfer,good temperature uniformity,and no power consumption,heat pipes can be widely used for heat dissipation of electronic components.This paper reports an experimental thermal analysis of different capillary structures for heat pipes.The wicks considered are metal screens,axial microgrooves,and sintered metal powder.The heat pipes are made of copper,a 200 mm length tube and a 9.45 mm external diameter.Working fluid used was distilled water.The devices are investigated in three positions:0,90,and 270°to the horizontal under powers of 5 up to 45 W.The results show that in horizontal(0°)and with the evaporator under the condenser(270°),the heat pipes showed similar results.Nevertheless,in the reverse condition(the position against the gravity with the evaporator above the condenser,90°),the heat pipe with sintered wick presented the best thermal performance,as it has the lowest thermal resistance and supported a higher power.Besides that,the sintered powder capillary structure demonstrates the most homogeneous thermal behavior for every position,making the most suitable for applications susceptible to diverse inclinations.
文摘Multiple loop heat pipe is a high-functional thermal transport device. This work was conducted to confirm the working performance of Multiple loop heat pipe under thermal vacuum ambience with the working fluid ammonia. Asmall multiple loop heat pipe with two evaporators and two ra- diators was designed and fabricated. Then thermal vacuum test was conducted. The heaters were fasten on both evaporators, both radiators, both compensation chambers. In the case that both evaporators were heated, the multiple loop heat pipe can transport 120/120 W for 1.5 m, in the case that only one evaporator was heated, evaporator 1 can transport 80 W for 1.5 m, while eva- porator 2 can transport 120 W for 1.5 m. Two flow regulators were installed near the confluence of liquid line to prevent uncondensed vapor penetrating into returning liquid when the tempera- ture difference exists between two radiators. In the case that the heat load at both evaporators were 40/40 W and one radiator was heated, the flow regulator1 can tolerate the 160 W of heat load which was supplied to radiator1 while the flow regulator2 can tolerate the 100 W of heat load which was supplied to radiator2. To demonstrate the multiple loop heat pipe’s startup behavior at lowheat load, each of the compensation chamber was preheated to change the initial distribution of liquid and vapor in the evaporator and compensation chamber, in the result, each evaporator can start up at 5W through preheating.