Characteristics Of Spray Atomization And Wall Film Cooling Of Bi-component Mixtures

The ever-changing technological developments continue to impose higher requirements on computing power.However,the heat dissipation of electronic components has repeatedly restricted the advance of high-power electronic equipment,and spray cooling has become the most promising cooling method currently due to its excellent heat exchange efficiency and distinctive applicability to present background.In this paper,the two stages of spray field and spray cooling are researched successively.Foremost,based on the experimental data of droplet size distribution,a numerical model of the spray field is established in FLUENT software.Thereafter,based on the experimental data of heat transfer characteristics,the spray cooling processes of diverse cooling fluids are simulated in order to investigate the involved mechanism by analyzing the distribution of adhered film thickness and film velocity on the heated surface.(1)The particle size distributions of pure water and 4% ethanol-water spray under different pressures were measured applying PDIA equipment.It was found that the droplet size gradually increased as deviating the spray center until reaching the maximum value,whilst there is a swift decrease followed.Besides the overall particle size distribution is "bimodal".On the basis of experimental measurement,the mathematical models involved in the simulation of the spray field were verified.(2)The heat transfer characteristics of these working fluids including pure water,ethanol-water(2%-6%)and isopropanol-water(1%-4%)were measured by the spray cooling experimental platform.It is noticed that the relationship between the heat transfer coefficients of ethanol-water mixed working fluid is 4%>6%>2% and that of isopropyl alcohol-water mixed working fluid is 2%>4%>1%.Moreover,that of pure water,4% ethanol-water and 2% isopropanol-water is 4% ethanol-water>2% isopropanol-water>pure water.And the heat transfer coefficients of two alcohol-water mixtures are both significantly greater than that of pure water.(3)In order to investigate the relationship and functional mechanism between wall film thickness and film velocity distribution and heat transfer capacity,the spray cooling processes of these cooling working fluids were simulated.It was concluded that the wall film thicknesses distribution formed by cooling fluid of the same category were similar under the identical heat flux,nonetheless,as the heat flux increased,the wall film thickness curve corresponding to the working fluid with optimum concentration appeared "sinking".It can be interpreted as,when the additive concentration is lower than the optimal value,the bubbles generated in the wall film have insufficient promoting effect on the thinning of wall film;when the concentration is higher than the optimal value,the bubbles are too dense which results in the locally accumulation of adhered film.In addition,the relationship between wall film velocity and heat transfer capacity is consistent.It can be explained as,when the alcohol concentration is lower than the optimal value,the reduction in surface tension and contact angle has inadequate impact on the acceleration of film motion;when the concentration is higher than the optimal value,the wall film motion is suppressed by the denser bubbles and the accumulation of more volatile gas at the gas-liquid interface.