Aerodynamic and Thermal Analysis of Bump Type Gas Foil Thrust Bearing for Cryogenic Helium Turboexpander

Abstract

Gas Foil Bearings (GFBs) are used for several high-speed applications for its compliant behavior to tailor its damping and stiffness. One of the highspeed application is the cryogenic turboexpander and they are used to refrigerate the gas stream in a liquefier. This article deals with the aerodynamic and thermodynamic analysis of bump type gas foil thrust bearings (BGFTBs), which are used to support the axial load of the helium turboexpander with a design speed of 2,40,000 rpm. The BGFTBs consists of very thin top and bump foils attached to the bearing base. The wedging action between the shaft collar and top foil is responsible for the development of aerodynamic pressure and this aerodynamic pressure supports the axial load of the rotor. Due to restricted converging passage for the gas flow between the collar and top foil, the process gas is likely to rise in temperature and distort the thin foils of the bearings. This paper presents a simulation method to analyze the aerodynamic and thermal behavior of the BGFTBs. The gas film is modeled using Reynold’s equation. The structural and Reynold’s equations are coupled together to predict the film thickness, pressure distribution and load carrying capacity. Further, the gas film is modeled by using an energy equation to predict the thermal characteristics. The Couette Approximation is used to predict the temperature distribution of the gas film. This approximation helps to delink the energy equation with Reynolds equation.