In this paper,we introduce the design principle of the oscillating excited spray cooling experimental device.We then designed an oscillating excited spray cooling experimental device.By using the device,the swaying mo...In this paper,we introduce the design principle of the oscillating excited spray cooling experimental device.We then designed an oscillating excited spray cooling experimental device.By using the device,the swaying motion can be realized through the control system,and the motion of the droplet under different vibration frequencies can be observed.By measuring the liquid flow rate and pressure,the changes in liquid flow rate,pressure,and temperature with time under different vibration frequencies were studied.The trajectory of the droplet and the temperature distribution of the droplet under different vibration frequencies could be observed.The device has a simple structure,is easy to control,and can achieve continuous observation of the spray cooling process.展开更多
Effective thermal control systems are essential for the reliable working of insulated gate bipolar transistors （IGBTs） in many applications. A novel spray cooling loop system with integrated sintered porous copper w...Effective thermal control systems are essential for the reliable working of insulated gate bipolar transistors （IGBTs） in many applications. A novel spray cooling loop system with integrated sintered porous copper wick （SCLS-SPC） is proposed to meet the requirements of higher device level heat fluxes and the harsh environments in some applications such as hybrid, fuel cell vehicles and aerospace. Fuzzy logic and proportional-integral-derivative （PID） policies are applied to adjust the electronic temperature within a safe working range. To evaluate the thermal control effect, a mathematical model of a 4-node thermal network and pump are established for predicting the dynamics of the SCLS-SPC. Moreover, the transient response of the 4 nodes and vapor mass flowrate under no control, PID and Fuzzy-PID are numerically investigated and discussed in detail.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 order to predict the pressure drop, collection efficiency, velocity, temperature and mole fraction of vapor in an industrial venturi scrubber with water spraying for converter gas cooling, a three-dimensional model...In order to predict the pressure drop, collection efficiency, velocity, temperature and mole fraction of vapor in an industrial venturi scrubber with water spraying for converter gas cooling, a three-dimensional model of heat and mass transfer with phase change is established. The gas flow and liquid droplets are treated as a continuous phase with a Eulerian approach and as a discrete phase with a Lagrangian approach, respectively. The coupled problem of heat, force, and mass transfers between gas flow and liquid droplets is solved by a commercial computational fluid dynamics（CFD） package, FLUENT. The numerical results show that the water injections have an important influence on the distributions of pressure, velocity, temperature, and mole fraction of vapor, especially for the spraying region in the throat. In the spraying region, the pressure drop is higher and the velocity is lower than in other regions due to the gas-droplet drag, while the temperature is lower because the droplet absorbs large amounts of heat from the high temperature gas and the mole fraction of vapor is higher due to the phase change of the liquid droplet. A number of cases with different Water-to-gas volume flow ratios and baffle openings were simulated. The dependence of pressure drop, velocity, temperature, mole fraction of vapor, and collection efficiency on both the water-to-gas volume flow ratio and baffle opening are analyzed. The good agreements between simulation results and experiment data of pressure drop, temperature, and collection efficiency validate the model. The model should facilitate optimization of the venturi scrubber design in order to give better performance with lower pressure drops and higher collection efficiency.展开更多
As an efficient cooling method for high heat flux field,spray cooling has a great application potential on aircraft directed energy weapon cooling.Based on previous research results,an experimental system of open-loop...As an efficient cooling method for high heat flux field,spray cooling has a great application potential on aircraft directed energy weapon cooling.Based on previous research results,an experimental system of open-loop spray cooling was established,and the potassium chloride aqueous solutions and ethylene glycol aqueous solutions with different mass fractions were applied to investigate the influence of different additives on spray cooling system performance.Besides,theoretical analysis was conducted according to the droplet breakage principle and the characteristic parameters of fluid mechanics.The results indicate that heat transfer can be enhanced by adding potassium chloride up to a certain concentration and then decrease with higher concentration.Heat transfer is deteriorated with the increase of ethylene glycol concentration.Both of the two additives can reduce the freezing point of the system,and ethylene glycol is preferred to improve the application range of the system in consideration of the corrosion of salt solution.展开更多
Aiming at the problem of air-cooled condenser output limit, a spray humidification system was presented to reduce the inlet air temperature. The pressure atomizing nozzle TF8 was chosen for inlet air spray cooling, an...Aiming at the problem of air-cooled condenser output limit, a spray humidification system was presented to reduce the inlet air temperature. The pressure atomizing nozzle TF8 was chosen for inlet air spray cooling, and the spray cooling experiment with different layouts of nozzles were conducted. Through heat and mass transfer analysis, the cooling effect fitting correlation was acquired with evaporative cooling being the major cooling mechanism. The experimental results under different nozzle layouts show that when the product of dry ball and wet ball temperature difference and spray rate is smaller than 75 ~C-m3/h, opening the TF8 nozzles in row 1 and row 2 （row distance is 500 mm） has better cooling effect than those in row 1 and row 3 （row distance is 1 000 mm）, while when the product is larger than 75 ~C＇m3/h, opening the TF8 nozzles in row 1 and row 3 is superior in cooling effect to those in row 1 and row 2.展开更多
With its high strength and hardness, wear-resistant steel has become an important material in the field of construction machinery manufacturing.Given that quenching technology is a crucial component of wear-resistant ...With its high strength and hardness, wear-resistant steel has become an important material in the field of construction machinery manufacturing.Given that quenching technology is a crucial component of wear-resistant steel production, the selection of the cooling method to be used during this process is important.In this study, the feasibility of quenching wear-resistant steel by air-atomized water spray cooling was studied, and the cooling rate, microstructure, and hardness of wear-resistant steel under various cooling device structures were analyzed.The results reveal that the air-atomized water spray cooling method is an effective technique in quenching wear-resistant steel.Furthermore, martensite and uniform hardness were obtained by the air-atomized water spray cooling technique.As the space between the nozzles in each row in the device increased, the cooling rate was reduced during quenching.Meanwhile, the martensite content decreased, and more carbides were observed in the martensitic structure.A mixture comprising self-tempered martensite and bainite was formed at a large distance over a longer period of time.All these factors resulted in lower hardness and worse property uniformity.展开更多
We present a new Nusselt number correlation for spray cooling at large Reynolds numbers and high surface temperatures for water sprays impinging perpendicularly onto a flat plate. A large set of experimental data on s...We present a new Nusselt number correlation for spray cooling at large Reynolds numbers and high surface temperatures for water sprays impinging perpendicularly onto a flat plate. A large set of experimental data on spray cooling of hot surfaces with water has been analyzed, including the water temperature effects. For large-scale cooling, such as in industrial processes, large number of injection parameters such as number, type, pressure, and angle of the spray injection has led to a multitude of correlations that are difficult for general and practical applications. However, by synthesizing a set of experimental data where all of the above parameters have been varied, we find that the Nusselt number and therefore the heat transfer coefficient can be cast accurately as a function of the Reynolds number. Water is widely used as the coolant during spray cooling, and has a specific phase change characteristic. At large Reynolds number (Re > 100,000) and surface temperature (Ts > 600°C) ranges, which are of interest in large-scale spray cooling, the effect of water temperature is quite significant as it affects the film boiling close to the surface. This effect also has been parameterized using experimental data.展开更多
Droplets are ubiquitous in nature and play an essential role in spray cooling,which is a highly efficient cooling approach for high-power-density miniaturized electronic devices.However,conventional pressure-driven sp...Droplets are ubiquitous in nature and play an essential role in spray cooling,which is a highly efficient cooling approach for high-power-density miniaturized electronic devices.However,conventional pressure-driven spray faces significant challenges in controlling microdroplet characteristics,particularly the droplet size and spray direction,both of which critically impact cooling performance.Herein,to conquer these challenges,we designed an acoustic microdroplet atomizer composed of a lead zirconate titanate(PZT)transducer and silicon inverted pyramid nozzles.This design enables precise control of droplet generation,overcoming the limitations of traditional spray methods.The acoustic atomization technology minimizes excess liquid accumulation while significantly enhancing thin liquid film evaporation.Compared to the conventional droplet generation techniques such as pressure-driven,injector-based,and piezoelectric spray,our acoustic atomizer achieves superior cooling performance.Notably,we demonstrate a high heat flux of∼220W/cm2 with a 3.6-fold enhancement at a low flow rate of 24 mL/min,achieving significantly improved cooling efficiency.Finally,our acoustic atomizer provides precise control over droplet size,velocity,and flow rate by adjusting the number of nozzles and the PZT transducer’s resonant frequency,elevating spray cooling performance.This novel acoustic atomization cooling technology holds great promise for practical applications,particularly in the thermal management of compact electronic components.展开更多
In spray cooling systems designed for airborne equipment or confined packaging conditions,the angle between the spray direction and gravity,known as the gravity angle,significantly affects cooling performance.This stu...In spray cooling systems designed for airborne equipment or confined packaging conditions,the angle between the spray direction and gravity,known as the gravity angle,significantly affects cooling performance.This study employed the Euler-Lagrange method to build a numerical model for spray cooling with four commonly used working fluids:R134a,HFE-7100,ethyl alcohol,and water.The study investigated the flow and heat transfer characteristics of spray cooling at different gravity angles.The results show that changes in the gravity angle alter the forces acting on the droplets during movement,promoting the aggregation of small droplets into larger ones,which leads to differences in droplet size distribution.This also causes varying degrees of viscous dissi-pation,resulting in a decrease in average droplet velocity.A nonzero gravity angle introduces a gravity component along the surface direction,causing asymmetry in the velocity and thickness of the liquid film.The region opposite this component exhibits a low-speed,thick liquid film,while the other side shows a high-speed,thin liquid film.These changes in liquid film flow due to the gravity angle affect heat transfer performance.The effect of the gravity angle varies for different working fluids.When the gravity angle increases from 0◦to 180◦,for low-viscosity and low-surface-tension fluids,such as R134a and HFE-7100,the maximum surface temperature difference exhibits an M-shaped variation,and the mean temperature remains constant.For high-viscosity and high-surface-tension fluids,such as ethyl alcohol and water,both the maximum temperature difference and mean temperature show a U-shaped variation,with optimal heat transfer performance at a gravity angle of 90◦.These differences are attributed to the physical properties of the working fluids,which result in variations in liquid film distribution and energy conversion during the spray-cooling process.展开更多
Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence,communications,electric vehicles,defense and aerospace sectors.Spray cool...Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence,communications,electric vehicles,defense and aerospace sectors.Spray cooling,which combines forced convection with phase-change latent heat of working fluids,is promising for high flux heat dissipation.Most of the previous studies on spray cooling enhancement adopted high spray flow rates to strengthen forced convection for high critical heat flux(CHF),leading to a low heat transfer coefficient(HTC).Micro/nanostructured surfaces can enhance boiling,but bubbles inside the structures tend to form a vapor blanket,which can deteriorate heat transfer.This work demonstrates simultaneous enhancement of CHF and HTC in spray cooling by improving both evaporation and liquid film boiling on three-dimensional(3D)ordered hierarchical micro/nano-structured surface.The hierarchical micro/nano-structured surface is designed to coordinate the transport of spray droplets,capillary liquid films,and boiling bubbles to enhance spray cooling performance.Boiling inversion where superheat decreases with increasing heat flux is observed,leading to an ultra-high HTC due to the simultaneous promotion of bubble nucleation and evaporation.Unprecedented CHF is obtained by overcoming the liquid–vapor counterflow,i.e.,synergistically facilitating bubble escape and liquid permeation.A record-breaking heat transfer performance of spray cooling is achieved with a maximum heat flux of1273 W/cm^(2)and an HTC of 443.7 kW/(m^(2)K)over a 1 cm^(2)heating area.展开更多
The current study focuses on spray cooling applied to the heat exchange components of a cooling tower.An optimization of such processes is attempted by assessing different spray flow rates and droplet sizes.For simpli...The current study focuses on spray cooling applied to the heat exchange components of a cooling tower.An optimization of such processes is attempted by assessing different spray flow rates and droplet sizes.For simplicity,the heat exchanger of the cooling tower is modeled as a horizontal round tube and a cooling tower spray cooling model is developed accordingly using a computational fluid dynamics(CFD)software.The study examines the influence of varying spray flow rates and droplet sizes on the heat flow intensity between the liquid layer on the surface of the cylindrical tube and the surrounding air,taking into account the number of nozzles.It is observed that on increasing the spray flow strength,the heat flow intensity and extent of the liquid film in the system are enhanced accordingly.Moreover,the magnitude of droplet size significantly impacts heat transfer.A larger droplet size decreases evaporation in the air and enhances the deposition of droplets on the round tube.This facilitates the creation of the liquid film and enhances the passage of heat between the liquid film and air.Increasing the number of nozzles,while maintaining a constant spray flow rate,results in a decrease in the flow rate of each individual nozzle.This decrease is not favorable in terms of heat transfer.展开更多
Dual Synthetic Jets (DSJ) can directly affect the development of spray through the complex vortex structure. The mechanism of flow control on spray and its thermal management application are studied by combining exper...Dual Synthetic Jets (DSJ) can directly affect the development of spray through the complex vortex structure. The mechanism of flow control on spray and its thermal management application are studied by combining experiment and simulation. The spray characteristics under different injection angles are studied, and the results show that the angle should be controlled in the range of 45°–60°, so that sufficient momentum transfer can be obtained, and meanwhile spray impingement area narrowing can be avoided. The spray characteristics under flow control of DSJ with different Reynolds numbers are studied, and the results show that Reynolds number should be controlled in the range of 2859–3574, so that strong particle streamwise acceleration and wall film disturbing can be achieved. In addition, the DSJ kinetic energy is utilized more efficiently. On the basis of previous research, this paper proposes a novel active heat pipe based on spray controlled by DSJ. The space occupancy has been reduced by more than 60%. Even in a sealed state, the active heat pipe is able to cool a hot surface with heat flux of 22.2 kW/m^(2) from 111℃ to 57℃ only in 20 s. The noise of DSJ is reduced from 85 dB to 60 dB, which is expected to promote the practical application of DSJ in thermal management.展开更多
To address the current issues with the conventional slide gate system utilized in the steel teeming process,a unique electromagnetic induction controlled automated steel teeming(EICAST)technology has been developed.Co...To address the current issues with the conventional slide gate system utilized in the steel teeming process,a unique electromagnetic induction controlled automated steel teeming(EICAST)technology has been developed.Cooling means of spiral coil in this technology is directly related to its service life.Firstly,heat transfer processes of air cooling and spray cooling were compared and analyzed.Secondly,the impacts of water temperature,water flow rate and air flow rate were examined in order to maximize the spray cooling effect.To maintain coil temperature at a low value consistently throughout the entire thermal cycle process of the ladle,a combined cooling mode was finally employed.Numerical simulation was applied to examine the coil temperature variation with different cooling systems and characteristics.Before coil operation,spray cooling is said to be more effective.By controlling the water flow rate and air flow rate,the spray cooling effect is enhanced.However,water temperature has little or no impact when using spray cooling.Air cooling during the secondary refining process and spray cooling prior to coil operation are combined to further lower coil temperature.When the direction of the spray cooling is from bottom to top,the coil temperature is lowered below 165℃.A practical induction coil cooling plan was provided for the EICAST technology’s production process.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
In this study,the heat transfer characteristics of nanofluids used in spray cooling systems were examined.Three nanofluids,i.e.,Cu,CuO,and Al2 O3,respectively,with volume fractions ranging from 0.1%to0.5%,as well as d...In this study,the heat transfer characteristics of nanofluids used in spray cooling systems were examined.Three nanofluids,i.e.,Cu,CuO,and Al2 O3,respectively,with volume fractions ranging from 0.1%to0.5%,as well as different volume fractions of a surfactant Tween 20,were used.In addition,their contact angles were measured to examine the heat-transfer characteristics.Under the same experimental conditions,with the increase in the volume fraction of the Cu nanoparticles from 0.1%to 0.5%,the maximum heat flux qmax increased from 3.36 MW/m2 to 3.48 MW/m2 from the impinging central point to r=30 mm(r is the distance from the impingement point),and the corresponding temperature of qmax increased from 400℃to 420℃.Results revealed that with increasing Tween 20 concentrations,the contact angle decreased because of the decrease in the surface tension of nanofluids and improvement of the wetting ability,and the corresponding qmax increased from 3.48 MW/m2 to 3.94 MW/m2 at the impact central point.展开更多
An experimental investigation was performed to study the heat transfer in an eight-nozzle spray cooling system with de-ionized water as the working fluid. Visualization of the liquid-solid contact area and the flow ne...An experimental investigation was performed to study the heat transfer in an eight-nozzle spray cooling system with de-ionized water as the working fluid. Visualization of the liquid-solid contact area and the flow near the heated surface was made using a microscopic lens system in conjunction with an advanced high-speed camera. The film thickness and film wavelike characteristics under liquid volume flow rates ranged from 2.78×10 -6 m 3 /s to 1.39×10 -5 m 3 /s and surface temperatures between 22℃ and 78.2℃ were examined respectively. The development process of the liquid film on the heated surface was observed. The local mean film thickness, the film wavelike characteristics and the behavior of the bubbles appeared in the liquid film were captured using an image processing technique. It is discovered that there exists a climax of local mean film thickness during the starting process of spray cooling. When the liquid film reaches the dynamic stable state, the dimensionless mean film thickness decreases with the increase of the liquid volume flow rate, and increases with the increase of surface temperature generally. Besides, the volume flow rate has a more significant impact on the wavelength and amplitude of the liquid film compared to the surface temperature.展开更多
Visualization experiments are carried out to investigate the atomization characteristics of R1336mzz flash spray cooling.The influences of superheat,spray distance,and nozzle orifice diameter on spray cooling performa...Visualization experiments are carried out to investigate the atomization characteristics of R1336mzz flash spray cooling.The influences of superheat,spray distance,and nozzle orifice diameter on spray cooling performance are analyzed experimentally.As the superheat increases,finer droplets and thinner liquid film are observed;this is helpful to improve the two-phase heat transfer efficiency.Enlarging atomization angle under high superheat is also observed for flash spray cooling,and it benefits for reducing the spray distance.It can be found that when the inlet superheat is 19.8℃ and the spray distance is 6 mm,the critical heat flux(CHF)reaches 251 W/cm^(2) and the maximum heat transfer coefficient(HTC)reaches 37.4 kW/(m^(2)℃),which are 55%and 11.6%higher than those when the inlet subcooling is 6.9℃ and the spray distance is 12 mm,respectively.Using flash spray reduces the spray distance,which benefits for designing compact spray cooling device.In addition,the nozzle orifice diameter has great influence on the cooling performance of flash spray,and the choice of the nozzle depends on the superheat.This study provides a physical insight into the heat transfer enhancement in flash spray cooling.展开更多
To improve the heat dissipation performance,this paper proposes a novel hybrid cooling method for high-speed high-power Permanent Magnet assisted Synchronous Reluctance Starter/Generator(PMa Syn R S/G)in aerospace app...To improve the heat dissipation performance,this paper proposes a novel hybrid cooling method for high-speed high-power Permanent Magnet assisted Synchronous Reluctance Starter/Generator(PMa Syn R S/G)in aerospace applications.The hybrid cooling structure with oil circulation in the housing,oil spray at winding ends and rotor end surface is firstly proposed for the PMa Syn R S/G.Then the accurate loss calculation of the PMa Syn R S/G is proposed,which includes air gap friction loss under oil spray cooling,copper loss,stator and rotor core loss,permanent magnet eddy current loss and bearing loss.The parameter sensitivity analysis of the hybrid cooling structure is proposed,while the equivalent thermal network model of the PMa Syn R S/G is established considering the uneven spraying at the winding ends.Finally,the effectiveness of the proposed hybrid cooling method is demonstrated on a 40 k W/24000 r/min PMa Syn R S/G experimental platform.展开更多
The increasing power density in applications such as aerospace,nuclear power,laser weapons,and phased array radar has led to a growing demand for efficient thermal management technologies.Spray cooling,known for its h...The increasing power density in applications such as aerospace,nuclear power,laser weapons,and phased array radar has led to a growing demand for efficient thermal management technologies.Spray cooling,known for its high heat flux dissipation and excellent temperature uniformity,has garnered great interest.Micro/nano-structured surfaces have been adopted to enhance spray cooling,especially in the phase-change heat transfer regime.However,manipulating bubble dynamics for non-interfering liquid and vapor flow paths remains a challenge under high heat flux conditions.This work employs a costeffective laser drilling technique to fabricate patterned multilayer perforated copper micromesh surfaces to enhance spray cooling.By creating separated liquid-vapor flow paths,bubble escape resistance is reduced,and the formation of vapor blankets within the perforated micromesh stack is delayed.Increasing the diameter and decreasing the separation between the perforations can strengthen the liquid and vapor transport,while reducing the liquid film boiling area.An analysis of flow resistance along bubble escape paths,caused by the anisotropic permeability of the multilayer micromesh in different directions,is performed to optimize the design of perforated microporous structures.A critical heat flux(CHF)of 1213 W/cm^(2),with a heat transfer coefficient(HTC)of 352.6 kW/(m^(2)K),is achieved on the patterned perforated micromesh surface,which is an improvement of 115%and 142%,respectively,compared to the plain surface.展开更多
基金The Natural Science Foundation of the Jiangsu Higher Education Institutions of China(22KJD580001)Jiangsu Maritime Institute Innovation Technology Funding Project(kicx2020-2)。
文摘In this paper,we introduce the design principle of the oscillating excited spray cooling experimental device.We then designed an oscillating excited spray cooling experimental device.By using the device,the swaying motion can be realized through the control system,and the motion of the droplet under different vibration frequencies can be observed.By measuring the liquid flow rate and pressure,the changes in liquid flow rate,pressure,and temperature with time under different vibration frequencies were studied.The trajectory of the droplet and the temperature distribution of the droplet under different vibration frequencies could be observed.The device has a simple structure,is easy to control,and can achieve continuous observation of the spray cooling process.
文摘Effective thermal control systems are essential for the reliable working of insulated gate bipolar transistors （IGBTs） in many applications. A novel spray cooling loop system with integrated sintered porous copper wick （SCLS-SPC） is proposed to meet the requirements of higher device level heat fluxes and the harsh environments in some applications such as hybrid, fuel cell vehicles and aerospace. Fuzzy logic and proportional-integral-derivative （PID） policies are applied to adjust the electronic temperature within a safe working range. To evaluate the thermal control effect, a mathematical model of a 4-node thermal network and pump are established for predicting the dynamics of the SCLS-SPC. Moreover, the transient response of the 4 nodes and vapor mass flowrate under no control, PID and Fuzzy-PID are numerically investigated and discussed in detail.
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 Beijing Novel Program, China (Grant No. 2008B16)
文摘In order to predict the pressure drop, collection efficiency, velocity, temperature and mole fraction of vapor in an industrial venturi scrubber with water spraying for converter gas cooling, a three-dimensional model of heat and mass transfer with phase change is established. The gas flow and liquid droplets are treated as a continuous phase with a Eulerian approach and as a discrete phase with a Lagrangian approach, respectively. The coupled problem of heat, force, and mass transfers between gas flow and liquid droplets is solved by a commercial computational fluid dynamics（CFD） package, FLUENT. The numerical results show that the water injections have an important influence on the distributions of pressure, velocity, temperature, and mole fraction of vapor, especially for the spraying region in the throat. In the spraying region, the pressure drop is higher and the velocity is lower than in other regions due to the gas-droplet drag, while the temperature is lower because the droplet absorbs large amounts of heat from the high temperature gas and the mole fraction of vapor is higher due to the phase change of the liquid droplet. A number of cases with different Water-to-gas volume flow ratios and baffle openings were simulated. The dependence of pressure drop, velocity, temperature, mole fraction of vapor, and collection efficiency on both the water-to-gas volume flow ratio and baffle opening are analyzed. The good agreements between simulation results and experiment data of pressure drop, temperature, and collection efficiency validate the model. The model should facilitate optimization of the venturi scrubber design in order to give better performance with lower pressure drops and higher collection efficiency.
文摘As an efficient cooling method for high heat flux field,spray cooling has a great application potential on aircraft directed energy weapon cooling.Based on previous research results,an experimental system of open-loop spray cooling was established,and the potassium chloride aqueous solutions and ethylene glycol aqueous solutions with different mass fractions were applied to investigate the influence of different additives on spray cooling system performance.Besides,theoretical analysis was conducted according to the droplet breakage principle and the characteristic parameters of fluid mechanics.The results indicate that heat transfer can be enhanced by adding potassium chloride up to a certain concentration and then decrease with higher concentration.Heat transfer is deteriorated with the increase of ethylene glycol concentration.Both of the two additives can reduce the freezing point of the system,and ethylene glycol is preferred to improve the application range of the system in consideration of the corrosion of salt solution.
基金National Key Technologies R&D Program in the 12th Five-Year Plan of China(No. 2011BAJ08B09)
文摘Aiming at the problem of air-cooled condenser output limit, a spray humidification system was presented to reduce the inlet air temperature. The pressure atomizing nozzle TF8 was chosen for inlet air spray cooling, and the spray cooling experiment with different layouts of nozzles were conducted. Through heat and mass transfer analysis, the cooling effect fitting correlation was acquired with evaporative cooling being the major cooling mechanism. The experimental results under different nozzle layouts show that when the product of dry ball and wet ball temperature difference and spray rate is smaller than 75 ~C-m3/h, opening the TF8 nozzles in row 1 and row 2 （row distance is 500 mm） has better cooling effect than those in row 1 and row 3 （row distance is 1 000 mm）, while when the product is larger than 75 ~C＇m3/h, opening the TF8 nozzles in row 1 and row 3 is superior in cooling effect to those in row 1 and row 2.
文摘With its high strength and hardness, wear-resistant steel has become an important material in the field of construction machinery manufacturing.Given that quenching technology is a crucial component of wear-resistant steel production, the selection of the cooling method to be used during this process is important.In this study, the feasibility of quenching wear-resistant steel by air-atomized water spray cooling was studied, and the cooling rate, microstructure, and hardness of wear-resistant steel under various cooling device structures were analyzed.The results reveal that the air-atomized water spray cooling method is an effective technique in quenching wear-resistant steel.Furthermore, martensite and uniform hardness were obtained by the air-atomized water spray cooling technique.As the space between the nozzles in each row in the device increased, the cooling rate was reduced during quenching.Meanwhile, the martensite content decreased, and more carbides were observed in the martensitic structure.A mixture comprising self-tempered martensite and bainite was formed at a large distance over a longer period of time.All these factors resulted in lower hardness and worse property uniformity.
文摘We present a new Nusselt number correlation for spray cooling at large Reynolds numbers and high surface temperatures for water sprays impinging perpendicularly onto a flat plate. A large set of experimental data on spray cooling of hot surfaces with water has been analyzed, including the water temperature effects. For large-scale cooling, such as in industrial processes, large number of injection parameters such as number, type, pressure, and angle of the spray injection has led to a multitude of correlations that are difficult for general and practical applications. However, by synthesizing a set of experimental data where all of the above parameters have been varied, we find that the Nusselt number and therefore the heat transfer coefficient can be cast accurately as a function of the Reynolds number. Water is widely used as the coolant during spray cooling, and has a specific phase change characteristic. At large Reynolds number (Re > 100,000) and surface temperature (Ts > 600°C) ranges, which are of interest in large-scale spray cooling, the effect of water temperature is quite significant as it affects the film boiling close to the surface. This effect also has been parameterized using experimental data.
基金National Natural Science Foundation of China,Grant/Award Number:52476060。
文摘Droplets are ubiquitous in nature and play an essential role in spray cooling,which is a highly efficient cooling approach for high-power-density miniaturized electronic devices.However,conventional pressure-driven spray faces significant challenges in controlling microdroplet characteristics,particularly the droplet size and spray direction,both of which critically impact cooling performance.Herein,to conquer these challenges,we designed an acoustic microdroplet atomizer composed of a lead zirconate titanate(PZT)transducer and silicon inverted pyramid nozzles.This design enables precise control of droplet generation,overcoming the limitations of traditional spray methods.The acoustic atomization technology minimizes excess liquid accumulation while significantly enhancing thin liquid film evaporation.Compared to the conventional droplet generation techniques such as pressure-driven,injector-based,and piezoelectric spray,our acoustic atomizer achieves superior cooling performance.Notably,we demonstrate a high heat flux of∼220W/cm2 with a 3.6-fold enhancement at a low flow rate of 24 mL/min,achieving significantly improved cooling efficiency.Finally,our acoustic atomizer provides precise control over droplet size,velocity,and flow rate by adjusting the number of nozzles and the PZT transducer’s resonant frequency,elevating spray cooling performance.This novel acoustic atomization cooling technology holds great promise for practical applications,particularly in the thermal management of compact electronic components.
基金supported by the National Natural Science Foundation of China(Grant No.:52076164)the National Science and Tech-nology Major Project of China(Grant No.:J2019-Ⅲ-0010-0054).
文摘In spray cooling systems designed for airborne equipment or confined packaging conditions,the angle between the spray direction and gravity,known as the gravity angle,significantly affects cooling performance.This study employed the Euler-Lagrange method to build a numerical model for spray cooling with four commonly used working fluids:R134a,HFE-7100,ethyl alcohol,and water.The study investigated the flow and heat transfer characteristics of spray cooling at different gravity angles.The results show that changes in the gravity angle alter the forces acting on the droplets during movement,promoting the aggregation of small droplets into larger ones,which leads to differences in droplet size distribution.This also causes varying degrees of viscous dissi-pation,resulting in a decrease in average droplet velocity.A nonzero gravity angle introduces a gravity component along the surface direction,causing asymmetry in the velocity and thickness of the liquid film.The region opposite this component exhibits a low-speed,thick liquid film,while the other side shows a high-speed,thin liquid film.These changes in liquid film flow due to the gravity angle affect heat transfer performance.The effect of the gravity angle varies for different working fluids.When the gravity angle increases from 0◦to 180◦,for low-viscosity and low-surface-tension fluids,such as R134a and HFE-7100,the maximum surface temperature difference exhibits an M-shaped variation,and the mean temperature remains constant.For high-viscosity and high-surface-tension fluids,such as ethyl alcohol and water,both the maximum temperature difference and mean temperature show a U-shaped variation,with optimal heat transfer performance at a gravity angle of 90◦.These differences are attributed to the physical properties of the working fluids,which result in variations in liquid film distribution and energy conversion during the spray-cooling process.
基金National Natural Science Foundation of China(52036002)。
文摘Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence,communications,electric vehicles,defense and aerospace sectors.Spray cooling,which combines forced convection with phase-change latent heat of working fluids,is promising for high flux heat dissipation.Most of the previous studies on spray cooling enhancement adopted high spray flow rates to strengthen forced convection for high critical heat flux(CHF),leading to a low heat transfer coefficient(HTC).Micro/nanostructured surfaces can enhance boiling,but bubbles inside the structures tend to form a vapor blanket,which can deteriorate heat transfer.This work demonstrates simultaneous enhancement of CHF and HTC in spray cooling by improving both evaporation and liquid film boiling on three-dimensional(3D)ordered hierarchical micro/nano-structured surface.The hierarchical micro/nano-structured surface is designed to coordinate the transport of spray droplets,capillary liquid films,and boiling bubbles to enhance spray cooling performance.Boiling inversion where superheat decreases with increasing heat flux is observed,leading to an ultra-high HTC due to the simultaneous promotion of bubble nucleation and evaporation.Unprecedented CHF is obtained by overcoming the liquid–vapor counterflow,i.e.,synergistically facilitating bubble escape and liquid permeation.A record-breaking heat transfer performance of spray cooling is achieved with a maximum heat flux of1273 W/cm^(2)and an HTC of 443.7 kW/(m^(2)K)over a 1 cm^(2)heating area.
基金supported by the National Natural Science Foundation of China(Grant No.52376069)Shandong Province Science and Technology Small and Medium sized Enterprise Innovation Ability Enhancement Project(Grant No.2022TSGC2596).
文摘The current study focuses on spray cooling applied to the heat exchange components of a cooling tower.An optimization of such processes is attempted by assessing different spray flow rates and droplet sizes.For simplicity,the heat exchanger of the cooling tower is modeled as a horizontal round tube and a cooling tower spray cooling model is developed accordingly using a computational fluid dynamics(CFD)software.The study examines the influence of varying spray flow rates and droplet sizes on the heat flow intensity between the liquid layer on the surface of the cylindrical tube and the surrounding air,taking into account the number of nozzles.It is observed that on increasing the spray flow strength,the heat flow intensity and extent of the liquid film in the system are enhanced accordingly.Moreover,the magnitude of droplet size significantly impacts heat transfer.A larger droplet size decreases evaporation in the air and enhances the deposition of droplets on the round tube.This facilitates the creation of the liquid film and enhances the passage of heat between the liquid film and air.Increasing the number of nozzles,while maintaining a constant spray flow rate,results in a decrease in the flow rate of each individual nozzle.This decrease is not favorable in terms of heat transfer.
基金supported by the National Natural Science Foundation of China(Nos.U2341202,12402333).
文摘Dual Synthetic Jets (DSJ) can directly affect the development of spray through the complex vortex structure. The mechanism of flow control on spray and its thermal management application are studied by combining experiment and simulation. The spray characteristics under different injection angles are studied, and the results show that the angle should be controlled in the range of 45°–60°, so that sufficient momentum transfer can be obtained, and meanwhile spray impingement area narrowing can be avoided. The spray characteristics under flow control of DSJ with different Reynolds numbers are studied, and the results show that Reynolds number should be controlled in the range of 2859–3574, so that strong particle streamwise acceleration and wall film disturbing can be achieved. In addition, the DSJ kinetic energy is utilized more efficiently. On the basis of previous research, this paper proposes a novel active heat pipe based on spray controlled by DSJ. The space occupancy has been reduced by more than 60%. Even in a sealed state, the active heat pipe is able to cool a hot surface with heat flux of 22.2 kW/m^(2) from 111℃ to 57℃ only in 20 s. The noise of DSJ is reduced from 85 dB to 60 dB, which is expected to promote the practical application of DSJ in thermal management.
基金supported by the Startup Foundation of Shenyang Agriculture University(No.X2023050)the Fundamental Research Funds for the Central Universities(No.N2209006)the National Natural Science Foundation of China(No.U22A20173).
文摘To address the current issues with the conventional slide gate system utilized in the steel teeming process,a unique electromagnetic induction controlled automated steel teeming(EICAST)technology has been developed.Cooling means of spiral coil in this technology is directly related to its service life.Firstly,heat transfer processes of air cooling and spray cooling were compared and analyzed.Secondly,the impacts of water temperature,water flow rate and air flow rate were examined in order to maximize the spray cooling effect.To maintain coil temperature at a low value consistently throughout the entire thermal cycle process of the ladle,a combined cooling mode was finally employed.Numerical simulation was applied to examine the coil temperature variation with different cooling systems and characteristics.Before coil operation,spray cooling is said to be more effective.By controlling the water flow rate and air flow rate,the spray cooling effect is enhanced.However,water temperature has little or no impact when using spray cooling.Air cooling during the secondary refining process and spray cooling prior to coil operation are combined to further lower coil temperature.When the direction of the spray cooling is from bottom to top,the coil temperature is lowered below 165℃.A practical induction coil cooling plan was provided for the EICAST technology’s production process.
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 National Key R&D Plan(Project No.2017YFB0305103)National Natural Science Foundation of China(Grant No.51404058)+1 种基金the fundamental research funds for the central universities(Grant No.N150704005)the open project of the RAL at Northeastern University(Grant No.2016006)。
文摘In this study,the heat transfer characteristics of nanofluids used in spray cooling systems were examined.Three nanofluids,i.e.,Cu,CuO,and Al2 O3,respectively,with volume fractions ranging from 0.1%to0.5%,as well as different volume fractions of a surfactant Tween 20,were used.In addition,their contact angles were measured to examine the heat-transfer characteristics.Under the same experimental conditions,with the increase in the volume fraction of the Cu nanoparticles from 0.1%to 0.5%,the maximum heat flux qmax increased from 3.36 MW/m2 to 3.48 MW/m2 from the impinging central point to r=30 mm(r is the distance from the impingement point),and the corresponding temperature of qmax increased from 400℃to 420℃.Results revealed that with increasing Tween 20 concentrations,the contact angle decreased because of the decrease in the surface tension of nanofluids and improvement of the wetting ability,and the corresponding qmax increased from 3.48 MW/m2 to 3.94 MW/m2 at the impact central point.
基金supported by the National Natural Science Foundation of China under Grant No.50906083National Basic Research Program of China under Grant No.2011CB710705
文摘An experimental investigation was performed to study the heat transfer in an eight-nozzle spray cooling system with de-ionized water as the working fluid. Visualization of the liquid-solid contact area and the flow near the heated surface was made using a microscopic lens system in conjunction with an advanced high-speed camera. The film thickness and film wavelike characteristics under liquid volume flow rates ranged from 2.78×10 -6 m 3 /s to 1.39×10 -5 m 3 /s and surface temperatures between 22℃ and 78.2℃ were examined respectively. The development process of the liquid film on the heated surface was observed. The local mean film thickness, the film wavelike characteristics and the behavior of the bubbles appeared in the liquid film were captured using an image processing technique. It is discovered that there exists a climax of local mean film thickness during the starting process of spray cooling. When the liquid film reaches the dynamic stable state, the dimensionless mean film thickness decreases with the increase of the liquid volume flow rate, and increases with the increase of surface temperature generally. Besides, the volume flow rate has a more significant impact on the wavelength and amplitude of the liquid film compared to the surface temperature.
基金supported by the National MCF Energy R&D Program(Grant No.2018YFE0312300)the National Natural Science Foundation of China(Grant No.51706102).
文摘Visualization experiments are carried out to investigate the atomization characteristics of R1336mzz flash spray cooling.The influences of superheat,spray distance,and nozzle orifice diameter on spray cooling performance are analyzed experimentally.As the superheat increases,finer droplets and thinner liquid film are observed;this is helpful to improve the two-phase heat transfer efficiency.Enlarging atomization angle under high superheat is also observed for flash spray cooling,and it benefits for reducing the spray distance.It can be found that when the inlet superheat is 19.8℃ and the spray distance is 6 mm,the critical heat flux(CHF)reaches 251 W/cm^(2) and the maximum heat transfer coefficient(HTC)reaches 37.4 kW/(m^(2)℃),which are 55%and 11.6%higher than those when the inlet subcooling is 6.9℃ and the spray distance is 12 mm,respectively.Using flash spray reduces the spray distance,which benefits for designing compact spray cooling device.In addition,the nozzle orifice diameter has great influence on the cooling performance of flash spray,and the choice of the nozzle depends on the superheat.This study provides a physical insight into the heat transfer enhancement in flash spray cooling.
基金co-supported by the National Natural Science Foundation of China(No.52177028)in part by the Aeronautical Science Foundation of China(No.201907051002)。
文摘To improve the heat dissipation performance,this paper proposes a novel hybrid cooling method for high-speed high-power Permanent Magnet assisted Synchronous Reluctance Starter/Generator(PMa Syn R S/G)in aerospace applications.The hybrid cooling structure with oil circulation in the housing,oil spray at winding ends and rotor end surface is firstly proposed for the PMa Syn R S/G.Then the accurate loss calculation of the PMa Syn R S/G is proposed,which includes air gap friction loss under oil spray cooling,copper loss,stator and rotor core loss,permanent magnet eddy current loss and bearing loss.The parameter sensitivity analysis of the hybrid cooling structure is proposed,while the equivalent thermal network model of the PMa Syn R S/G is established considering the uneven spraying at the winding ends.Finally,the effectiveness of the proposed hybrid cooling method is demonstrated on a 40 k W/24000 r/min PMa Syn R S/G experimental platform.
基金supported by the National Natural Science Foundation of China(Grant No.52036002)。
文摘The increasing power density in applications such as aerospace,nuclear power,laser weapons,and phased array radar has led to a growing demand for efficient thermal management technologies.Spray cooling,known for its high heat flux dissipation and excellent temperature uniformity,has garnered great interest.Micro/nano-structured surfaces have been adopted to enhance spray cooling,especially in the phase-change heat transfer regime.However,manipulating bubble dynamics for non-interfering liquid and vapor flow paths remains a challenge under high heat flux conditions.This work employs a costeffective laser drilling technique to fabricate patterned multilayer perforated copper micromesh surfaces to enhance spray cooling.By creating separated liquid-vapor flow paths,bubble escape resistance is reduced,and the formation of vapor blankets within the perforated micromesh stack is delayed.Increasing the diameter and decreasing the separation between the perforations can strengthen the liquid and vapor transport,while reducing the liquid film boiling area.An analysis of flow resistance along bubble escape paths,caused by the anisotropic permeability of the multilayer micromesh in different directions,is performed to optimize the design of perforated microporous structures.A critical heat flux(CHF)of 1213 W/cm^(2),with a heat transfer coefficient(HTC)of 352.6 kW/(m^(2)K),is achieved on the patterned perforated micromesh surface,which is an improvement of 115%and 142%,respectively,compared to the plain surface.
