Abstract
A high-pressure pneumatic catapult works under extreme boundaries such as high-pressure and rapid change of pressure and temperature, with the features of nonlinearity and gas-solid convection. In the thermodynamics processes, the pressure is much larger than the critical pressure, and the compressibility factor can deviate from the Zeno line significantly. Therefore, the pneumatic performance and thermo-physical properties need to be described with the real gas hypothesis instead of the ideal gas one. It is found that the analytical results based on the ideal gas model overestimate the performance of the catapult, in comparison to the test data. To obtain a theoretical model with dynamic leakage compensation, leakage tests are carried out, and the relationship among the leakage rate, pressure and stroke is fitted. The compressibility factor library of the equation of state for compressed air is established and evaluated by referring it to the Nelson-Obert generalized compressibility charts. Based on the Peng–Robinson equation, a theoretical model of the high-pressure pneumatic catapult is developed, in which the effects of dynamic leakage and the forced convective heat transfer between the gas and the metal wall are taken into account. The results from the theoretical model are consistent with the data from ejection tests. This research presents an approach to study the performance of a high-pressure pneumatic catapult with high precision.
Highlights
High-pressure pneumatic catapult works with high-pressure air, which has the advantages of no pollution, inexpensive nature, recycling, high power density and stable performance [1]
The pressure is much higher than the critical pressure, and the compressibility factors deviate from the Zeno line significantly
The research on the theoretical modelling of a high-pressure catapult with a high velocity, in which the compressed air with strong instantaneous expansibility is chosen with a consideration of dynamic leakage and convective heat transfer is rarely reported, nor is the for the pneumatic catapult [10,11]
Summary
High-pressure pneumatic catapult works with high-pressure air, which has the advantages of no pollution, inexpensive nature, recycling, high power density and stable performance [1]. Few studies take the real gas effects and the convective heat transfer into consideration high-pressure pneumatic catapult with an open-type cylinder is adopted to drive a heavy object at the same time. The research on the theoretical modelling of a high-pressure catapult with a high velocity, in which the compressed air with strong instantaneous expansibility is chosen with a consideration of dynamic leakage and convective heat transfer is rarely reported, nor is the for the pneumatic catapult [10,11]. Leakage tests of the pneumatic catapult were forced convective heat transfer between the working medium and the metal wall in the real gas carried out to obtain a precise model for dynamic leakage, by fitting the relationship among leakage state, an accurate theoretical model of a high-pressure pneumatic catapult was established, which rate, pressure and stroke. This research provides support for designing and optimizing high-pressure pneumatic catapults
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