Designing an Experimental Device for Swinging Excitation Spray Cooling

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.

Development of Energy-storing High Pressure Spray Cooling System

The greenhouse has been increasingly used in the breeding industry. However, the high temperature inside the greenhouse in summer has not been effectively addressed. The spray cooling system sprays tiny droplets into the air. Thus the water molecules will be vaporized, absorbing heat and reducing ambient temperature. It is the only cooling method that can be used to cool the uneasily-sealed flexible greenhouse. We developed an energy-storing high pressure spray cooling system. The ordinary water pump is used as the source of high-pressure water. The partial kinetic energy is stored in the energy-storing tubes. When the water pump is stopped, the energy produced by releasing the compressed air can still be used to maintain the spray. And thus the use-cost and systematic wear would be reduced. The cooling system only requires 1 kilowatt hour of power per day. It has been widely used in summer to cool the breeding sheds. After a recent continuous improvement, its functions have been extended to disinfection, removing dust, humidifying and immunizing animals. In addition, it can also be used for the cooling and humidifying of squares, venues and streets in summer. The energy-storing high pressure spray cooling system has a broad application prospect.

Numerical Simulation of Three-dimensional Heat and Mass Transfer in Spray Cooling of Converter Gas in a Venturi Scrubber

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.

Experiment on Spray Cooling Performance with Different Additives of Different Mass Fraction

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.

Experimental Study on Spray Cooling Performance of Pressure Atomizing Nozzle

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.

Effects of air-atomized water spray cooling device structure on the quenching process,microstructure,and properties of wear-resistant steel

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.

Heat Transfer during Spray Cooling of Flat Surfaces with Water at Large Reynolds Numbers

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.

Simulation Study on the Heat Transfer Characteristics of a Spray-Cooled Single-Pipe Cooling Tower

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.

Transient performance and intelligent combination control of a novel spray cooling loop system

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.

Ground experimental investigations into an ejected spray cooling system for space closed-loop application

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.

Recent Advances in Closed Loop Spray Cooling and its Application in Airborne Systems

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.

Visualization of Film Wavelike Characteristics and Measurement of Film Thickness in Spray Cooling

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.

Visualization study on atomization characteristics and heat transfer performance of R1336mzz flash spray cooling

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.

Effect of Nanoparticle Type and Surfactant on Heat Transfer Enhancement in Spray Cooling

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.

Design and analysis of a novel hybrid cooling method of high-speed high-power permanent magnet assisted synchronous reluctance starter/generator in aviation applications

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.

Energy conversion characteristics of reciprocating piston quasi- isothermal compression systems using water sprays

Air compressors are vital and have numerous industrial applications. Approximately 8% of the annual operating electricity consumption in industrial countries is constituted by due to the use of air compressors. Because the poor heat transfer to the environment in the rapid compression process, the compression is non-isothermal, the efficiency of compressors is restricted. To improve their efficiency and achieve isothermal compression, this study proposes energy conversion reciprocating piston quasiisothermal compression using a water spray. First, a mathematical model of a reciprocating piston compressor with water sprays was established. Through experimental investigation and simulations, the mathematical model was validated. The energy conversion characteristics of the reciprocating piston compressor were then studied. To reduce compression power and enhance compression efficiency, it was first discovered that the critical parameters were the input pressure of the driving chamber, water spray mass, and compression volume ratio, which were then evaluated thoroughly. The higher the inlet pressure of the driving chamber, the faster the air compression velocity. Additionally, the compression efficiency was elevated as the water spray mass was gradually increased for a given compression volume ratio. When the compression volume ratio was increased from 2 to 3,the compression power increased from 172.7 J/stroke to 294.2 J/stroke and the compression efficiency was enhanced from 37.3%(adiabatic) to 80.6%. This research and its performance analysis can be referred to during the parameter design optimisation of reciprocating piston quasi-isothermal compression systems using water sprays.