Study On Performance Optimization Of Split Phase Thermosyphon Oil Cooling System

During the operation of screw compressor,the discharged lubricating oil must be cooled to maintain a lower oil supply temperature and improve the reliability and efficiency of the refrigeration system.Compared with other oil cooling methods,the split phase thermosyphon oil cooling system is suitable for screw refrigeration unit because of its reliability,flexibility and no need of driving pump.In this paper,the experimental platform of split phase thermosyphon oil cooling system was built,and the heat transfer,mass flow of refrigerant and outlet temperature of lubricating oil were measured under five working conditions.The theoretical models of split phase thermosyphon oil cooling system with different combination of heat transfer and pressure drop formulas are established and solved iteratively,and compared with the experimental values.The results show that for split phase thermosyphon oil cooling system,Ayub heat transfer model and Huang friction pressure drop model are selected for the refrigerant side of oil cooler,Friedel or CESNEF-2 friction pressure drop model are selected for the two-phase flow,and lockhard model is selected for calculating void fraction,which has the highest simulation accuracy.Based on the selected theoretical model of split phase thermosyphon oil cooling system,the fixed variable method is used to analyze the influence of structural parameters on its heat transfer performance.The results show that increasing the liquid level difference between thermosyphon tank and oil cooler,the diameter of downcomer 2 and two-phase pipe can improve the heat transfer of oil cooling system and reduce the temperature of lubricating oil outlet,while increasing the height difference between condenser outlet and thermosyphon tank and the length of connecting pipe will weaken the heat transfer performance of oil cooling system.The influence of operation parameters on heat transfer performance was studied by orthogonal analysis.The contribution rate of condensation temperature,inlet temperature of lubricating oil to heat transfer was 68.5%and 24.2% respectively,which was the main factor causing the change of heat transfer;the contribution rate of flow rate of lubricating oil to heat transfer was 7%,which was the secondary factor causing the change of heat transfer.The effect of resuming the liquid supply after the condenser stopped feeding for 1-5minutes on the heat transfer performance of the split phase thermosyphon oil cooling system was studied.It was found that the time from resuming the liquid supply to stable operation of the oil cooling system was about one third of the time of stopping the liquid supply.By optimizing the thermosyphon tank,the mixing loss of subcooling degree is eliminated and the subcooling degree of refrigerant at the inlet of oil cooler is reduced.Keep the condenser and oil cooler unchanged,the structural parameters of each component are optimized,and the optimized thermosyphon tank is integrated.The results show that the heat transfer of oil cooling system is increased by 16.8%-21%,the outlet temperature of lubricating oil is decreased by 4.4 ℃ on average,and the refrigeration capacity of the refrigeration unit is increased by 1.5% ～ 2.5%.