Sublimation Heat Transfer of Dry Ice Particle Spray with Array Laval Nozzle
Objective To meet the market demand,the performance of semiconductor lasers is continuously improving.In the digital era,the increasing integration of various electronic components is leading to a rapid increase in power densities and operating temperatures.During normal operations,approximately 40％-60％of the optical energy is converted into heat energy that is stored within the laser.The performances of semiconductor lasers are closely related to their thermal management.Research has shown that under adequate cooling conditions(the ideal state),significant enhancements can be achieved in terms of the emission efficiency,output power,beam quality,temperature stability,and reliability.The traditional cooling media for semiconductor lasers include R32,water,and liquid nitrogen,which dissipate heat under certain conditions.However,with a continuous increase in the laser heat flux density,traditional cooling media exhibit significant limitations.Carbon dioxide,which is a non-polar molecule with a simple structure,exists as a colorless and odorless gas in liquid and solid forms.When throttled to reduce the pressure to atmospheric levels,liquid carbon dioxide transforms into solid dry ice at extremely low temperatures.This study introduces dry ice as a cooling medium and proposes a novel array nozzle device.Combining jet impingement with dry ice phase-change cooling enables the efficient thermal management of high-heat flux density semiconductor lasers.Methods This study focused on practical stacked high-power semiconductor lasers.Initially,an array nozzle device utilizing dry ice cooling was designed based on the dry ice particle formation mechanism.The device primarily comprises jetting chambers,array nozzles,and simulated laser heat sources.During the modeling,a uniform arrangement with equal spacing and size in a parallel layout between the array nozzles and laser heat sources was adopted.The array nozzle configuration was 3X4 with a Laval nozzle consisting of a converging section,throat,and diverging section.Subsequently,computational fluid dynamics(CFD)software was employed to simulate the heat exchange process.For the sublimation heat transfer of dry ice and the two-phase flow heat transfer process,user-defined functions(UDF)were employed for the numerical simulation,thereby enabling the determination of the optimal nozzle parameters by varying the throat diameter of the Laval array nozzle and adjusting the spray height.These parameters were then applied to investigate the cooling characteristics of lasers with different heat flux densities using a relatively optimal nozzle configuration.Finally,through experimental validation and comparison with numerical simulation results,minor experimental errors were obtained,ensuring the feasibility of using Laval array nozzles for the dry ice cooling of high heat flux density semiconductor lasers.Results and Discussions The physical model of the Laval array nozzle dry ice sublimation heat transfer established in this study was used to analyze the influence of the throat diameter on the temperature uniformity of the laser and its cooling effect in local regions.The throat diameter affects the exit velocity,direction,and mass flow rate of the dry ice particle spray,thereby affecting the heat transfer effectiveness of dry ice particle spray cooling.When the throat diameter is＜4 mm,the temperature distribution at the impact position of the Laval array nozzle exhibits a ring shape.The interference between the nozzle outlet velocities decreases,resulting in lower temperatures closer to the center,whereas relatively higher temperatures occur in the edge and gap areas outside the region directly facing the jet impact.When the throat diameter is＜4 mm,the temperature of local high-temperature region largely remains within the safe operating range of the laser(Fig.2).At a spray height of 15 mm,there is a significant increase in the proportion of the high-temperature regions of the heat source.For lasers with heat flux densities below 100 W/cm2,it is advisable to maintain the spray height within a range of 10-15 mm(Fig.5).The temperatures at measurement points along the laser length at x=-10 mm,x=0 mm,and x=10 mm show minimal variation at heights of H=15-25 mm(Fig.6).Utilizing the relatively optimal nozzle configuration for cooling different heat flux density lasers,spray heights of H=5 mm,8 mm,and 10 mm can ensure that the temperatures of semiconductor lasers with heat flux densities of 165 W/cm2,156 W/cm2,and 125 W/cm2 do not exceed 40 ℃,with a heat transfer coefficient reaching up to 20113.47 W/(m2·K).This configuration guarantees the normal operation of kilowatt-level high-power semiconductor lasers(Fig.7).Conclusions Based on the Laval array nozzle dry ice particle sublimation cooling model,numerical simulations and experimental studies are conducted on the heat dissipation process of the laser.The research reveals that under the same heat flux density,a smaller throat diameter results in a higher spray outlet velocity,which leads to a lower average temperature and better temperature uniformity of the laser.With the same throat diameter,as the spray height decreases,the proportion of the low-temperature area increases,with a heat transfer coefficient of 19516 W/(m2·K)at 5-10 mm.As the heat flux density increases under the same spray height conditions,the temperature of the laser increases linearly.The array nozzle meets the requirements for the normal operation of lasers within 180 W/m2,with a heat transfer coefficient of 20470.82 W/(m2·K).
spray coolingdry ice sublimationarray nozzlenumerical simulationhigh heat flux density
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