A Study Of The Real Gas Effects On High Pressure Pneumatics And The Basic Theoretical And Experimental Researches Of Pressure Reduction System

The high pressure pneumatic system has been applied to armaments, air powered vehicle and compressed air energy storage owing to the unique characteristics such as huge instant dispensability, high power density. Most current researches of high pressure pneumatics are under ideal gas assumption. The researches of real gas effects in high pressure pneumatics, polytropic exponent in thermodynamic processes and energy transfer in the pneumatics of current literatures need improvement. And these preblems are the fundamental issues for the pneumatics, especially for high pressure pneumatic systems. This thesis first study the real gas effects on exergy, enthalpy, internal energy, charging and discharging processes and exergy efficiency of throttling for high pressure pneumatics. In addition, the polytropic exponent, energy and exergy transfers of an actual pressure reduction system have been studied on the basis of theories and experiments. The main contents are as follows:In chapter 1, the development status of high pressure pneumatics and valves are introduced. The current researches about the definition of compressed air energy, real gas effects, polytropic exponent and pneumatic capacitor model are summarized. The development of SER is also given out. Finally, the main research problem is proposed.In chapter 2, the exergy of high pressure real air is analyzed. An equation of exergy for real gases is first derived by judicious advised thermodynamic paths. The databases of air compressibility factors are obtained by Virial, P-R and S-R-K equations. The exergy for real air is calculated and the real gas effect on exergy is analyzed. It is found that the largest deviation between the exergies calculated by the real gas equations and under ideal gas assumption is about 1% when the air pressure is less than 30 MPa.In chapter 3, the real gas effects on air enthalpy and internal energy in the energy conversion of the pneumatics are estimated. Based on the relation among pressure, enthalpy and internal energy, the real gas effects on charging and discharging processes of high pressure pneumatics are studied. The results indicate that, for high pressure pneumatics, the pressure enthalpy and pressure internal energy of real pneumatic air obviously decrease the values of enthalpy and internal energy respectively. The real gas effect accelerates the temperature and pressure decreasing rates during discharging process, and decelerates their increasing rates during charging process. For convenient, this paper first proposes a method to compensate the real gas effect under ideal gas assumption by modulating the thermal capacity of the pneumatic container in simulation.In chapter 4, the exergy efficiency of throttle reduction is analyzed. The Joule-Thomson coefficients are used to calculate the temperature changes of throttling. The results show that, when the initial pressure of air is less then 30 MPa and throttling at atmospheric temperatures, heat exergy contributes very little in throttling, and the real gas effect on the throttling efficiency is little. Thus, the simple equation of ideal gas is suggested to calculate the efficiency of throttling for air at atmospheric temperatures.In chapter 5, the principle and experimental condition of SER are introduced. A comprehensive simulation model has been built for the experimental setup of SER. A number of the experimental results have been obtained. The experiments show that the simulation model well predicts the actual characteristics and SER shows high adaptability in pressure reduction ratios and output air mass flow rates. The experiments of SER support the compensating method in chapter 3.In chapter 6, the heat transfers and polytropic exponents of the air in expansion tank and supply tanks of SER have been studied. Through the mathematical reasoning, the polytropic processes model is connected with the heat transfer model and the first law. The value of the polytropic exponent can be obtained by the air mass, heat, and work exchanges of the pneumatic container. The polytropic exponents research of SER indicate that, for the air in a constant volume tank, when the heat-absorption is large enough to arouse an air temperature rise during discharging process, the polytropic exponent is less than 1; when the air is experiencing a discharging and heat-releasing process, the polytropic exponent exceeds the specific heat ratio (the value of 1.4). Meanwhile, the concept of pneumatic capacitor is used to simplify the simulation model of SER. The error characteristics of this simplified model are studied combining with the polytropic exponent analysis.In chapter 7, the energy balance, air internal energy, enthalpy and exergy transfers of SER are comparatively analyzed in this paper. In addition, the difference between exergy analysis and energy conversion analysis for the pneumatics are studied. Based on the above analyses, to improve the exergy efficiency of the pneumatics, the pressure reduction without power output should be avoided. Some advices are given for using compressed air as a secondary energy.In chapter 8, the major research work, conclusions and innovations of this thesis are elaborated. In addition, future development is predicted in order to provide references for the further research on this project.