Study The Rarefied Effects And Flow State Of Gas In Air Hydrostatic Guideway

Precise air hydrostatic guideway owns many advantages, such as high stiffness, high motion accuracy, non-polluting etc, so it was widely used in precise machine tools, coordinate measure machines and other equipments. The precision and stability of guide and are closely associated with film state. Restrictor flow pattern will form a high area from the intake port to the gas chamber, then the gas flows into the rail gap from this area to the outlet, which avoids the complex flow patterns problem of gas chamber area. But in fact it is possible to scroll cyclone and other phenomena in throttle position of gas chamber, which affects the stability of gas film and its pressure. As the thickness of air film guide is only in micron, sub-micron level, rarefied effect will occur and microscopic molecular motion such as speed slip and temperature jump phenomenon will be prominent to produce a non-negligible effect on the ability of loading pressure, mass flow, heat flotation etc.This paper will choose an appropriate throttle and explain the mechanism of pattern flow from inlet port to gas chamber, gas chamber to outlet and gas chamber cyclones and shock phenomenon depend on molecular dynamics respectively, adapt CFD to prove these phenomenon. During this process we propose stratified phenomenon, which was proved by simulation lately. For the effects of thin gas appears in film gap, we derive LBM based on Boltzmann equation, which was used to study the velocity distribution, temperature distribution as well as pressure distribution.During analysis we find that with Kn number increases, slippage rate will increase either, the pressure of transition area near the wall will reduce correspondingly, temperature jump in slippery zone is pretty gentle, but in transition zone, it becomes severe. As a result, velocity slip benefits film heat exchanger, temperature jumps equivalent to attach a thermal resistance between gas and wall membrane, which is conducive to heat dissipation. Due to theory analysis and pressure distribution, we try to get the relationship of velocity and pressure in stratification.