Study On The Characteristics Of Atomization Throttling And Low-pressure Distribution Of Refrigerant

In refrigeration or heat pump system,the two-phase refrigerant after throttling often flows into the evaporator coil unevenly,resulting in the reduction of the cooling(heat)capacity and the COPR This dissertation introduces atomization into the field of refrigeration creatively,the sub-cooled liquid-phase refrigerant is throttled and atomized into small droplets through the atomization nozzle,which not only result in better uniformity of the two-phase refrigerant,but also has the potential to enhance the two-phase refrigerant boiling heat transfer.In this paper,a atomization visualization test bench,a liquid distribution characteristics test bench and the corresponding mathematical model was established,to carry on the comprehensive analysis to the atomization throttling and the throttled two-phase refrigerant distribution.The main contents of the dissertation are as follows:1.Visualization experimental platform of atomization throttling was set up to judge the feasibility of atomization throttling directly.Through the transparent visible glass cavity,it is found that the fine atomization nozzle(0.4mm aperture)has a more satisfactory results,the main influencing factors of atomization throttling and the direction of modeling calculation are also clarified..2.In view of the results of visualization experiments,the simulation model of internal flow and external atomization flow field of the nozzle was established,the characteristics of single nozzle’s atomization throttling are analyzed based on the Euler method,Flow rate or nozzle’s outlet velocity distribution,velocity distribution of the atomization flow field,turbulent kinetic energy in the Atomization flow field(used to measure the atomization effect of the nozzle)was used as the measurement standard of nozzle throttling characteristic.The simulation results show that,in addition to the influence of aperture on flow rate,the influence of structure on atomization throttling is almost negligible compared to the simulated operating conditions.And reducing the temperature of evaporation and sub-cooling,improving the temperature of condensation are beneficial to the atomization.3.According to the simulation results of single nozzle’s atomization throttling,the atomization throttling device was designed,the dense discrete phase model was used to calculate the two-phase distribution characteristics of the newly designed atomizer throttling device,and set up test platform of liquid distribution performance,the characteristics of the liquid distribution were measured and the calculation model was validated.The results show that under the condition of low pressure test,compared with the experimental results,the error of the simulation results was less than 20%,and the relative error was about 15%in more than half of the working condition.It shows that the calculation model adopted in this paper had good accuracy.4.By using the established calculation model,the influence of the operating conditions and the structure factors on the two-phase distribution is further analyzed.We achieved the following conclusion:The liquid distribution characteristics can reach the level of the pressure drop and centrifugal distributor in most simulation conditions,The maximum flow deviation can reach to the storage distributor’s level.In this paper,the height and diameter of the atomizing cavity,the diameter and length of the outlet pipe are analyzed,and the influencing factors are arranged from large to small.It is found that reducing the size of the atomizing cavity suitably and widening the outlet diameter appropriately,can increase the two-phase distribution characteristic by about 20%.5.According to the calculation results of the structure,the paper mainly optimized the atomization cavity which is the two-phase mixing area and the distribution pipe.The atomization throttling device’s volume is reduced by nearly 74.5%through a series of improvements,fluctuation range of the liquid’s and gas’s maximum flow deviation narrows to 0.07～0.15 and 0.04～0.16,Two-phase distribution uniformity and stability have been greatly improved to a high level.