| Miniature high-pressure air compressor has broad applications in aviation,aerospace,and other civil high-end equipment fields.For improving the cleanliness and reducing the pollution of lubricating oil to air charging,oil-free lubrication is the development trend of micro air compressor and has a great attention at home and abroad.However,because of the use of oil-free lubrication method,the heat of friction pairs is serious.And it difficult to fully cool before the gas entering the next compressing stage due to the small size and insufficient cooling space of the micro compressor,which causes the temperature of compressor rise and long-term working under the condition of insufficient cooling,and effects the improvement of its working efficiency.Thus,this paper theoretically and experimentally investigates the working efficiency for micro-oil-free compressor under the condition of insufficient cooling.So the research results provide reference for the optimization of air compressor.The main work of this study is as follows:According to the working conditions and occasions of different air compressors and the technical indexes of this research,the overall structural scheme of miniature highpressure air compressor in this study is determined,and the miniature multi-stage compressor with a swash plate is proposed,in which an integrated inter-stage cooler is used for the inter-stage cooling.On this basis,the pressure,temperature and structural parameters of all compressing stages in miniature high-pressure air compressor are calculated,and the parameters of suction and discharge valves are calculated by numerical simulation in Workbench.Based on the thermodynamics,kinematics of air compressor and the dynamic characteristics equitation of valve,the efficiency prediction model of miniature air compressor are established.The process parameters of piston pressure,temperature,mass of gas,the valve opening and the volume efficiency and isentropic efficiency of each stage of the compressor can be monitored in real time through the model.In order to characterize the insufficient cooling conditions of air compressor,the differences between suction temperature of each compressing stage and that of first compressing stage are used as variables to simulate the thermodynamics of air compressor.The simulation results show that the higher the degree of insufficient cooling is,lower the compressing efficiency is.For every 10? increase in temperature,the isentropic efficiencies are all reduced by about 1% and the volumetric efficiency of first-stage to fourth-stage reduced by an average of 1.43%,1.86%,2.32%,and 2.56% respectively and the degree of decrease gradually increases.What's more,the total volumetric efficiency decreases with the increase of suction temperature of gas.Considering the sensibility of compressor compression efficiency to clearance volume,firstly,the model validation experiment of gas pressure in cylinder of single cylinder is carried out in this paper.The results show that the experimental results are in good agreement with the simulation results,and the coincidence degree is higher than 800 rpm and 600 rpm at 1000 rpm.On the basis of verifying the correctness of the model,the discharge pressure of each stage was tested by installing the pressure sensor on the interstage cooler.The volumetric efficiency of air compressor was calculated to be 47.76%,which was in good agreement with the simulation results.The research work in this paper reveals the coupling relationship between the compression efficiency,structure and operating parameters of air compressor under the condition of insufficient cooling,thus providing a theoretical basis for the optimization design and further improvement of the efficiency of the micro high-pressure air compressor. |
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