Oil flow from compressor valve to discharge tube

compressor;oil;two-phase flow;visualization;simulation

Xu, Jiu ; Hrnjak ; Predrag Stojan

关键词: compressor;    oil;    two-phase flow;    visualization;    simulation;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/90682/XU-THESIS-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Oil existence is important for compressor operation because it provides lubrication, cooling and sealing. But the discharge process of the compressor inevitably entrains some oil in the refrigerant vapor, which makes oil leave compressor and circulate in the system. For better heat transfer and refrigerant distribution, it is preferable to reduce the mass flow rate of oil in system circulation. Visualization of closing and opening of the compressor discharge valve shows the how oil enters into the compressor plenum. High speed videos are taken to look at the valve and the discharge tube in order to get the oil droplet size and velocity. Due to the difficulty of flow visualization in the plenum space, computational fluid dynamics (CFD) is used to simulate the oil flow from the valve to the discharge. Discrete phase model in CFD can calculate the oil droplet trajectory in a certain fluid field of refrigerant vapor. To validate the CFD simulation, size distribution from video processing at the valve is used as the input of the calculation and the calculation results are compared to size distribution in the discharge tube. Potential oil separation structure design inside the compressor plenum is also compared based on the simulation.Compressors produce annular-mist flow consisting of refrigerant vapor flow with oil film and oil droplets in the discharge tube. Discharge tube is the most accessible location for oil flow visualization and quantification. A non-invasive method based on high speed video and optical measurement is developed to estimate the oil retention and oil circulation ratio by measuring oil film thickness, oil film average velocity, oil droplet size and oil droplet velocity. The estimated oil retention and oil circulation ratio results are compared with the measurements from sampling in the experiments under different compressor speeds. The agreement between the video results and the sampling measurements verify the accuracy of the non-invasive method. It is also shown oil film dominates by mass while oil droplets contributes more to the oil mass flow rate because oil droplets travel in a much higher speed. The quantitative information of oil flow in the compressor discharge tube provides guidance to oil separator design and separation efficiency evaluation.