Study On Liquid Quantity Of U-tube Accumulator

The accumulator is an important auxiliary equipment in refrigeration system,which can effectively reduce the risk of"liquid slugging"of compressor,but its introduction makes it difficult to return oil to the compressor.In this paper,the mathematical model of the U-tube accumulator is established,the U-tube accumulator with visible components is designed,and an open experimental device is built by using air and water.The influence of liquid level height outside the U-tube,gas flow velocity inside the tube,inner diameter of the U-tube and diameter of liquid return hole on the liquid quantity at the outlet is analyzed.The main contents of this paper are as follows:1.Through the quasi-static model of full liquid flow,the liquid flow condition of full liquid flow is qualitatively analyzed,and it is verified by experiments that when full liquid flow occurs,the U-tube will periodically discharge a large amount of liquid instantaneously.2.The influence of various parameters in the mixed flow model on the liquid quantity at the outlet is simulated by MATLAB,and the accuracy of the mixed flow model in predicting the influence of liquid level on liquid quantity is verified by experiments.The maximum deviation of liquid quantity at outlet between the model and the experiment is less than 6%when the air velocity is 2.48 m/s and the height difference of liquid level is 45 to 193.5 mm.3.The velocity and pressure distribution of air in the elbow are simulated by MATLAB and FLUENT.The simulation results show that when the air velocity is constant,the greater the ratio of the elbow radius to the inner diameter of U-tube,the more uniform the pressure in the pipe section:when the air velocity is 12 m/s and the R/d_t?2,the pressure non-uniformity in the pipe section is less than 100 Pa;when the air velocity is 12 m/s and the R/d_t?4,the pressure non-uniformity in the pipe section is less than 50 Pa.4.The experimental results show that there are five different flow patterns in the U-tube when the gas velocity is between 0.626 m/s and 22.42 m/s:full liquid flow,churn flow,annular flow,stratified flow and mist flow.When the diameter of liquid return hole is 1.5 mm,the critical velocity of full liquid flow to churn flow is 0.626 m/s,and the deviation is 5.6%compared with the critical velocity of 0.661 m/s calculated by the liquid film model,while the deviation is 2078.91%compared with the critical velocity of 13.64 m/s calculated by the single drop model.It is proved that the liquid film model is more suitable for calculating the critical velocity of full liquid flow to churn flow than the single drop model.