Study On The Spray And Its Characteristics Of Heat Transfer Enhancement Based On Dual Synthetic Jets

With the development of manufacturing technology and craft level,many military equipment such as high power laser weapons,microwave power device,phased array radar,airborne facility,computer chips etc.are developing towards high frequency and high integration.The heat flux increases sharply,and the surface temperature rises continuously,which has become a bottleneck restricting their further development.What’s more,in the future,this heat dissipation problem will also develop towards the demand for large areas of enhancement of heat transfer.It’s urgent to develop new heat dissipation technologies to maintain the components temperatures safely.Combine the outstanding heat dissipation ability of spray cooling with the flow field control ability of dual synthetic jet,which is expected to break through the heat dissipation problem of large-area equipment with high temperature and high heat flux in a restricted space.Based on the actual heat dissipation demand,this article imposed an innovation heat dissipation method by combining the above two cooling technology,which not only has the advantages of compact structure,low energy consumption,easy to control,high turbulence,benefits in heat transfer enhancement,but also has the prominent heat dissipation ability of two-phase spray cooling.In this article,miniaturized and integrated dual synthetic jet spray cooling actuators are designed and studied.Firstly,a dual synthetic jet actuator integrated with a piezoelectric atomizer(DSJAPA)is proposed and designed.The experimental results show that the spray angle increases with the increase of driving voltage,from 20°to 74°,and the direct impacting area of spray increases by more than 2 times.Under a certain driving voltage,there exists an optimum driving frequency making the spray angle reach to the maximum.The spray flow field is investigated by droplet image velocimetry(PIV)system.The results show that the spray droplet velocity can be accelerated to about 22.5m/s by the high-speed ejection of the jet.With the increase of dual synthetic jet velocity,the dense spray with low velocity changes into the dilute spray with high velocity.A dual synthetic jet actuator can improve the cooling capability of spray,reduce the temperature non-uniformity of surface(from 32℃in spray cooling to 18℃in DSJAPA cooling),which is of great significance to the heat dissipation of the temperature-sensitive devices.Depending on the difference between the pressure in the slots of the actuator and the ambience,water can enter into the slots and form liquid film without additional energy consumption,and then the liquid film will be broken up into spray droplets.Based on this atomization method,a novel dual synthetic jet actuator-based atomization device(DSJAA)is proposed and designed.The effects of driving voltage,driving frequency,fluid volumetric flow rate and spray height are investigated on atomization rate,water droplet size,surface temperature and heat flux.The maximum atomization rate is 3.4L/h at driving frequency of 700Hz and driving voltage of 210V.The dimensionless correlations between the physical properties of dual synthetic jet and the size of water droplet are presented,which provides guideline for the design of a dual synthetic jet actuator-based fluid atomizer.The experimental results show that when the resonance frequency of piezoelectric diaphragm is equal to half the Helmholtz frequency of DSJAA,the atomization performance is the best by setting driving frequency to resonance frequency.The best spray height is equal to the fluid stroke length of DSJAA.The cooling capability is mainly influenced by the Reynolds number of dual synthetic jet and volumetric flow rate of water.A correlation for DSJAA cooling is established.A maximum heat flux of the novel spray cooling method reaches as high as 59W/cm~2 in the experiments.The third one is a vectoring dual synthetic jet actuator integrated with piezoelectric atomizers,which is the structure optimization based on the first one.Depending on the different responses of two diaphragms to the same driving electrical signal,the asymmetric synthetic jets are generated and the vectoring function is realized.The research results show that the greater the thickness of the diaphragms is,the greater the difference in the response to the same driving signal is,and the larger the vectoring angle can achieve.The result also shows that Coanda effect can effectively promote the deflection of spray vectoring angle and enhance the vectoring function.The direct measurement of the vectoring angle in the flow field is compared with the angle calculated through the coordinate of the minimum temperature on the surface.The two are basically the same,therefore,when cooling the target surface,the fixed-point removal function of the high-temperature region can be realized.