Real-Gas Effects in Foil Thrust Bearings Operating in the Turbulent Regime

Abstract

In this study, an elastohydrodynamic model was created for predicting the pressure field in a compliant thrust bearing assembly lubricated by high pressure CO2. This application is of significance due to ongoing research into the closed-cycle supercritical CO2 turbine as a high-efficiency alternative to steam turbines. Hardware development for this concept has been led by Sandia National Laboratories, where turbomachinery running on gas foil thrust and journal bearings is being tested. The model accounts for the fluid velocity field, hydrodynamic pressure, and frictional losses within the lubrication layer by evaluating the turbulent Reynolds equation coupled with an equation for structural deformation in the bearings, and the fluid properties database RefProp v9.0. The results of numerical simulations have been compared with empirical correlations, with reasonable agreement attained. Of particular interest is the contrast drawn between the performance of high pressure CO2 as a lubricant, and ambient pressure air. Parametric studies covering a range of fluid conditions, operating speeds, and thrust loads were carried out to illustrate the value of this model as a tool for improved understanding and further development of this nascent technology.

A trade-off between maxima in efficiency and specific work output of super- and trans-critical CO2 Brayton cycles

“…The interest in CO 2 based cycles arises as a part of our effort to explore them for possible power generation using CSP [1,19]. There have been some studies suggesting the use of supercritical CO 2 for nuclear power generation also [19][20][21][22][23][24][25].…”

“…The objective of this paper is to further explore the above two path function coordinate system to understand the intricate link between the performance indicators and cycle operating parameters for the specific case of CO 2 Brayton cycle power plants. This study is motivated by recent developments in concentrated solar power using CO 2 based Brayton cycles [1,2,[18][19][20][21][22][23][24][25]. Recently, Mohagheghi et al [26] used Pareto-based multi objective optimization for optimizing the process parameters of transcritical regenerative CO 2 Brayton cycle.…”

Preliminary experimental study on static loading characteristics of multi-decked protuberant foil thrust bearing

“…Gas foil bearing (GFB) is a type of compliant surface hydrodynamic bearing that has been applied in rotating machinery with higher speed and heavier load, such as turbocharger , cryogenic turbo-expander (Andres, et al, 2014;Hou, et al, 2004), compressor (Conboy, 2013), generator , micro turbomachinery (Dykas, et al, 2013). Comparing to conventional ball bearing, foil bearing is outperformed with high speed, reliability, durability and wide temperature capabilities (Agrawal, 1997;Ryu K and Andres, 2013;Howard, et al, 2001aHoward, et al, , 2001bHeshmat, et al, 2005).…”

Control of a Supercritical CO2 Recompression Brayton Cycle Demonstration Loop

“…The CO2 within the housing was near 2.3 MPa and 44kg/m', elevated from a design point of 1.4 MPa, 26 kg/m'. Due to the strong sensitivity of the frictional power loss to fiuid density, even this relatively small difference can have a significant impact [5]. In this instance, the off-design pressure within the housing may be attributed to the underperformance of the scavenging pump system or advanced stages of wear on the abradable labyrinth seals.…”

“…Since the inception of this program in 2007, a number of the key questions surrounding this technology have already been identified and resolved. This includes achieving compressor stability and control near the critical point [4], devising high pressure approaches to bearings and seals [5], and developing control procedures from cold-startup to break-even conditions for a simple recuperated Brayton cycle [6]. Likewise, operation of a simple recuperated cycle during steady-state power production at 20 kWĥ as been reported in detail [7].…”