| In recent years,spray cooling technology has been favored by more and more scholars due to its advantages of high heat exchange efficiency,low demand for working fluid,and low temperature gradient,and more and more researches on spray cooling have been applied.The many advantages of spray cooling technology meet the requirements of cooling technology in the field of refrigeration and air conditioning.This paper innovatively introduces spray cooling technology into the field of refrigeration and air conditioning and applies it to the complete refrigeration cycle.At present,finned-tube heat exchangers are mostly used in the market to exchange heat with the cold room environment to achieve the purpose of reducing the temperature of the cold room.In order to reduce the complexity of the research work,this paper uses heating surfaces with different inclination angles to simplify practical application problems.A closed visualization refrigerant atomization spray evaporative refrigeration experimental bench is established,and the corresponding mathematical model is established,and the atomization spray evaporative cooling process in the experiment is simulated and calculated by CFD technology.The main research contents and conclusions of this paper are as follows:1.A closed visual refrigerant atomization jet evaporative refrigeration experimental bench is built.R134 a is used as the refrigerant.The refrigerant liquid can well achieve atomization and evaporative cooling in the evaporator through the nozzle of 0.45 mm aperture,and the cooled surface.The temperature is significantly reduced,and the refrigeration cycle consisting of the air-cooled condenser,throttling device,compressor and evaporator can operate normally,which proves the feasibility of applying the refrigerant atomization flash cooling technology to the field of refrigeration and air conditioning.2.By using pressure regulators,ceramic heating fins,height adjustment devices and heating surfaces with different inclination angles,the effects of heat flux density,nozzle height from the center point of the heating surface and the inclination angle of the heating surface on the refrigerant atomization spray evaporation heat transfer performance were explored.The influence of,and the changes of temperature,temperature difference and heat transfer coefficient when the heating surface is balanced under different working conditions are compared and analyzed,and the following conclusions are drawn:（1）Under the conditions of 70mm～130mm nozzle height and 15°～45° inclination angle used in this experiment.With the increase of heat flux density,the temperature of the heating surface at equilibrium increases continuously,the temperature difference of the heating surface increases continuously,and the heat transfer coefficient also increases continuously.It shows that the increase of heat flux density can significantly improve the heat transfer performance between the heating surface and the working fluid.（2）The nozzle heights used in the experiment are 70 mm,90mm,110 mm and 130 mm respectively.When the nozzle height is 110 mm,the spray cone is just tangent to the upper edge of the inclined heating surface.The study found that with the increase of the nozzle height,the temperature of the heating surface at equilibrium increased continuously,the temperature difference of the heating surface continued to decrease,and the heat transfer coefficient continued to decrease,and when the nozzle height increased from 110 mm to130mm,its heat transfer coefficient.The drop is significantly lower than the drop in heat transfer coefficient between the three heights of 70 mm,90mm and 110 mm.It shows that when the nozzle height is lower than the tangent height between the spray cone and the heating surface,the effective mass flow rate and the droplet velocity of the droplets falling on the heating surface have a significant effect on the heat transfer performance.When the nozzle height is tangent to the heating surface,the effect of the effective mass flow rate and the droplet velocity on the heat transfer performance is greatly reduced.（3）Three heating surfaces of 15°,30° and 45° were used in the experiment to explore the effect of the inclination angle on the evaporative cooling performance of the atomized spray.It was found that with the increase of the inclination angle of the heating surface,the temperature of the heating surface at equilibrium decreased continuously,and the temperature difference of the heating surface continued to increase,and the heat transfer coefficient continues to increase,but the increase of the heat transfer coefficient shows a trend of first increasing and then decreasing.When the inclination angle increases from 15°to 30°,the heat transfer coefficient increases.When the inclination angle is increased from30°to 45°,the heat transfer coefficient is only increased by 18.6%.It can be reasonably inferred that there is no limit to the improvement of heat transfer performance by increasing the inclination angle,and there is a most effective inclination angle.3.CFD was used to perform transient simulation calculation of the refrigerant atomization jet evaporative cooling process inside the evaporator,and obtain the atomization jet evaporative cooling process based on the DPM model,the component transport model and the Eulerian wall film model.The liquid droplet motion state and liquid film morphology were compared and analyzed on the heating surfaces with inclination angles of 0°,15°,30° and 45°,and the following conclusions were obtained:（1）The refrigerant droplets ejected from a high degree form a small area near the heating surface.Due to the existence of the inclined angle,a large-scale vortex is formed inside the evaporator cavity,and the vortex formed by the horizontal heating surface is obviously smaller than the vortex range of the inclined heating surface.It shows that the inclination angle can improve the turbulence of the working fluid in the space.（2）The maximum liquid film thickness in the range of 0°～30° inclination angle gradually decreases,and the coverage area of thicker liquid film continues to shrink.However,when the inclination angle increases from 30° to 45°,the maximum liquid film thickness gradually increases.It is presumed that the liquid film with a faster flow rate prevents the droplets from splashing and leaving the liquid film,resulting in a decrease in the liquid film thickness.increase. |
PDF Full Text Request