CFD Analysis of Aerostatic Bearing for Cryogenic Turbo-Expander

Abstract

Expansion turbine plays the major role in any cryogenic plants like helium and hydrogen liquefier,air separation plants and low temperature refrigerator.These turbines run at speed around 50,000 to 5,00,000 rpm.At such a high speed no bearing is feasible to support the load except gas bearing.In gas bearing there is no physical contact between stator and rotor takes place so the friction between the stator and rotor is negligible.Because of this the rotor can move smoothly inside the stator.Hence aerostatic bearing used for achieving high accuracy and precession. Due to cleanness of aerostatic bearing it is also used in electronic and food processing industry.In order to avoid complexities at the time of formulation analytical studies has been carried out.Governing variables are kept limited that helps in dynamic and performance conduct of aerostatic bearing.Finally a three dimensional model of aerostatic bearing was built in Solidworks and a two dimensional cross-section model of aerostatic bearing in ANSYS workbench 15. After doing rectangular meshing to the geometry made in workbench Computational fluid dynamics(CFD)analysis was done in ANSYS Fluent. The pressure and velocity distribution at the bearing clearance and at orifice had shown.It is found that there is rapid change in pressure and velocity at the exit of the orifice.Variation of Load carrying capacity with the change of inlet pressure was studied and compared with numerical value