Currently, experimental data on the physical properties of lubricants used in compressors is scarce, and suppliers or manufacturers only provide data on finite temperature points and pressure conditions. However, in the refrigeration system, the lubricating oil flows in the system, and the operating conditions of the refrigeration system vary greatly, even very bad. If the finite point data is still used for analysis and research, it will inevitably lead to large errors. In this paper, the lubricant property prediction model in the literature is used to study the change law of lubricating oil in the compressor, and the lubricating oil characteristics and compressor oil return characteristics of the new automatic oil balance oil separator are analyzed.
1 Lubricant property prediction model
The physical property parameters that lubricant suppliers can provide are specific gravity, viscosity at 38 ° C and 99 ° C. The molecular weight of the lubricant calculated from the three parameters in [4> is: viscosity at any temperature: where The density of liquid lubricating oil at atmospheric pressure and at any temperature is: Density at any temperature and pressure: according to the above model, the viscosity and density of the lubricating oil are varied with pressure and temperature. Among them, the lubricant grade is Idemisu Kosan FVC68D, the viscosity provided by the manufacturer at 37.78 ° C and 98.89 ° C is v 38 =66.66 (mm 2 /s), v 99 =8.04 (mm 2 /s), and the specific gravity SG is 0.9369 (g). /cm 3), the molecular weight calculated by formula (1) is 388. The viscosity has a strong nonlinearity with temperature. In the actual application process, the viscosity at two temperature points is interpolated to calculate the values ​​of other temperature points. The error is very large; the influence of pressure on the density of lubricating oil is small, the linearity of density changes with temperature, but the effect of temperature on density is still relatively large.
2 Analysis of oil throwing mechanism of new oil and gas separator
2.1 Principle analysis
There have been many researches on oil and gas separators used in refrigeration systems, and there are also special discussions on the principle and design of oil and gas separators. The new oil and gas separator studied in this paper is particularly characterized by the oil return pipe and compressor return oil. The oil separator separates the lubricating oil from the compressor exhaust and stores it at the bottom of the oil separator.
The oil return capillaries 3 and 8 are used to return the oil in the oil separator to the compressor return line to ensure sufficient oil during operation of the compressor.
The oil slinger 6 discharges the lubricating oil that is not needed by the compressor into the refrigeration system, and performs secondary distribution between different modules.
The principle of throwing oil in the oil pipe is to use the pressure difference caused by the difference in flow state at both ends of the oil pipe as the power of oil throwing. According to the principle of Bernoulli equation, the outlet pressure of the oil pipe and the inlet pressure difference are at the inlet of the oil pipe, and the speed of the oil can be approximated. Is zero, ie V 1 =0, then: 2.2 Reliability Analysis
The parallel compressor is made up of DC inverter compressor and conventional fixed frequency compressor in parallel. The displacement of the compressor is 37.5 cm 3 /rev and 59 cm 3 /rev respectively. The separation effect of the oil separator is calculated at 75% of full load. Calculated at 50% at low load. The oil separator outlet pipe specification is Φ12.7×0.8, the throwing pipe specification is Φ6.35×0.8, and the length of the slinger is 500 mm.
The working conditions of the compressor and the performance parameters of each operating point during the calculation are as follows: 1 DC inverter compressor 90Hz operation, full-load operation of the fixed-frequency compressor at the same time (Table 1); 2 DC-only inverter with 30Hz Low load conditions during operation (Table 2).
When the compressor is under full load and at low load, the exhaust mass flow rate m ref is calculated according to equations (12) and (13), respectively, m ref =0.174 kg/s at full load; m ref =0.0145 kg/s at low load .
The refrigerant flow rate in the outlet of the oil separator can be calculated according to formula (14), V 2 = 23.3 m / s at full load; V 2 = 1.8 m / s at low load.
The pressure difference between the inlet and outlet of the oil pipe can be calculated according to formula (15), then ΔP oil = 249802 Pa at full load and ΔP oil = 5988 Pa at low load.
The oil flow in the oil pipe can be calculated according to formula (16), Q oil_tube = 8.5834 × 10 -5 m 3 /s at full load; Q oil_tube = 0.21 × 10 -5 m 3 / s at low load.
The oil flow rate in the slinger is calculated according to equation (17), then V oil_tube = 5.645 m/s at full load and V oil_tube =0.136 m/s at low load.
The Reynolds number in the sling can be calculated according to equation (18), then Re oil_tube = 373 at full load; Re oil_tube = 10. at low load.
The drag coefficient can be calculated according to equation (19), f oil_tube = 0.18 at full load and f oil_tube = 6.4 at low load.
The flow resistance can be calculated according to formula (20), then 2473 Pa/m at full load and 1.5 Pa/m at low load.
The total resistance in the slinger can be calculated according to formula (21), ΔP=5041 Pa<ΔP oil =249802 Pa at full load; ΔP=3936 Pa<ΔP oil =5898 Pa. at low load.
From the above analysis, whether the oil pipe indenter is larger than the internal resistance of the oil pipe under full load conditions or under severe low load conditions, the oil in the oil separator higher than the height of the oil pipe inlet can be smoothly thrown. In the system piping.
1 fixed frequency compressor; 2 oil and gas separator; 3 fixed frequency compressor return pipe; 4 gas liquid separator; 5 oil pipe outlet; 6 oil sling pipe; 7 oil pipe inlet; 8 inverter compressor oil return pipe; Schematic diagram of new automatic oil balance oil separator
3 Conclusion
1) The nonlinearity of lubricating oil viscosity changes with temperature is very strong. The model used to predict the viscosity of lubricating oil has strong practicability and can simulate the viscosity at any temperature point. 2) The influence of system pressure on the density of lubricating oil is very small. However, the influence of temperature on density is relatively large; 3) The feasibility and reliability of the oil balance principle of the new automatic oil balance oil separator are analyzed by Bernoulli's equation principle, whether it is at full load or in harsh conditions. At low load, the oil slinger can function.
Symbols indicate A, B, C, D, E coefficients; d diameter, m; f resistance coefficient; h ratio ç„“, kJ/kg; H height, m; L length, m; m mass flow, kg/s; M molecular weight ;P pressure,bar;Q mass flow,kg/s;Re Relo numbers SG specific gravity, g/cm 3; S cross-sectional area, m 2; T temperature, K; V flow rate, m/s; ν dynamic viscosity, Mm 2 /s; Ï density, g/cm 3; μ kinematic viscosity, N/m.
Subscript: oil lubricant; oil_tube oil sling; ref refrigerant; low low load.
The above only lists the experimental results of some operating conditions and the comparison of the calculated results. From the experimental results and the comparison results of the results solved by the model, it can be seen that the experimental results and calculation results of several major quantities of refrigeration (heat) and the calculation results of each set of working conditions are small, and the error range is ±10%. Between ± 5%.
4 Summary
Based on the basic principles of thermodynamics and heat and mass transfer, this paper establishes a distributed parameter model for the calibration of the surface cooler using Visual Basic as the simulation platform. It can be seen from the comparison between the experimental results and the calculated results that the two agree The degree is good, so the accuracy of the watch cooler model is high, suitable for the simulation research of the air cooler, and has a certain guiding effect on the engineering application of the air cooler.
Symbol Description n 1 Number of tubes per row N Number of rows of tubes S 1 tube spacing, m S 2 row spacing, mdo water tube outer diameter, md 3 wing root diameter, mδf fin thickness, m S f fin spacing, mmw water mass flow , kg/sma air mass flow, kg/s
N-Ethylpyridinium Chloride,Cas 2294-38-4,N-Ethylpyridinium Chloride 2294-38-4,Pyridine Ionic Liquids
Henan Tianfu Chemical Co.,Ltd , https://www.hnionicliquids.com