Aerodynamic Analysis of Corrugated Bump-Type Gas Foil Thrust Bearing for High-speed Cryogenic Turboexpander used in Nitrogen Liquefaction Plant

Abstract

The recent development of high-speed turbomachinery such as cryogenic turboexpander restricts the use of liquid lubricated bearings as they have demerits such as contamination and high viscosity, which further leads to friction losses. To overcome the mentioned issues, gas lubricated bearings are used as they can withstand wide temperature range, avoid contamination and are reliable too. Recently, Gas Foil Bearings (GFBs) are used in place of simple gas bearings as they have low power losses along with high stiffness and damping characteristics. The present article deals with the study of aerodynamic behaviour of the gas foil thrust bearing (GFTB) for a vertically oriented cryogenic nitrogen turboexpander operating at 80,000 rpm. The numerical model is developed by using Reynold’s equation which helps to study the fluid flow behaviour of the axial bearing. Further, a structural equation is also used to consider the changes in film thickness due to the presence of spring-like bump foil. Both fluid flow and structural equation are coupled together and solved simultaneously to predict pressure profile over the bearing surface, the load-carrying capacity of the axial bearings, film thickness, deflection, power loss and frictional torque. The work is further extended to study the performance of the bearings over the variation of material and geometrical parameters of the bump and top foils.