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Technical Briefs

Thermal Performance Measurement of a Bump Type Gas Foil Bearing Floating on a Hollow Shaft for Increasing Rotating Speed and Static Load

[+] Author and Article Information
Tae Ho Kim

 Energy Mechanics Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, 136-791 Seoul, South Koreathk@kist.re.kr

Jin Woo Song

 Energy Mechanics Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, 136-791 Seoul, South Koreapowerfulguy@kist.re.kr

Yong-Bok Lee

 Energy Mechanics Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, 136-791 Seoul, South Korealyb@kist.re.kr

Kyuho Sim

 Energy Mechanics Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, 136-791 Seoul, South Koreakhsim@kist.re.kr

J. Eng. Gas Turbines Power 134(2), 024501 (Dec 08, 2011) (5 pages) doi:10.1115/1.4004401 History: Received March 31, 2011; Revised May 16, 2011; Published December 08, 2011; Online December 08, 2011

Identifying thermal characteristics of gas foil bearings (GFBs) provides an insight for successful implementation into high speed oil-free turbomachinery. The paper presents temperature measurements of a bump type GFB floating on a hollow shaft for various operating conditions. Two angular ball bearings support the hollow shaft at one end (right), and the other end (left) is free. Test GFB has the outer diameter of 100 mm and the axial length of 45 mm, and the hollow shaft has the outer and inner diameters of 60 mm and 40 mm, respectively. An electric motor drives the hollow shaft using a spline coupling connection. A mechanical loading device provides static loads on test GFB upward via a metal wire, and a strain gauge type load cell placed in the middle of the wire indicates the applied loads. During experiments for shaft speeds of 5 krpm, 10 krpm, and 15 krpm and with static loads of 58.9 N (6 kgf ), 78.5 N (8 kgf ), and 98.1 N (10 kgf ), twelve thermocouples measure the outer surface temperatures of test GFB at four angular locations of 45 deg, 135 deg, 215 deg, and 315 deg, with an origin at the top foil free end, and three axial locations of bearing centerline and both side edges at each angle. Two infrared thermometers measure the outer surface temperature of the hollow shaft at free and supported ends close to test GFB. Test results show that GFB temperatures increase as the shaft speed increases and as the static load increases, with higher temperatures in the loaded zone (135 deg and 215 deg) than those in the unloaded zone (45 deg and 315 deg). In general, the recorded temperatures are highest at 225 deg where a highest hydrodynamic pressure is expected to build up. Measured temperatures at the bearing centerline are higher than those at the side edges, as expected. In addition, large thermal gradients are recorded in the hollow shaft along the axial direction with higher temperatures at the supported end. The axial thermal gradient of the shaft is thought to cause higher temperatures at the bearing right edge facing the ball bearing support than those at the left edge. The paper presents test data along with detailed test GFB/shaft geometries and material properties.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Test GFB configuration and performance measurement test rig

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Figure 2

GFB displacement versus static load recorded during consecutive loading—unloading tests. Estimated nominal radial clearance Cnom  = 70 μm.

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Figure 3

Temperature measurement locations and preliminary measurement of shaft temperature without GFB. TR 1–5: noncontact infrared thermometer. TH 1–12: K-type thermocouples on bearing housing outer surface along left edge (L), centerline (C), and right (R) edge at circumferential positions of 45 deg, 135 deg, 225 deg, and 315 deg.

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Figure 4

Transient responses of measured temperatures at test GFB housing for increasing shaft speed from 5 krpm to 15 krpm with static load of 58.9 N (6 kgf ). Measurements at centerline (C), left end (L), and right end (R). Nominal radial clearance: 70 μm.

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Figure 5

Transient responses of measured temperatures at shaft and test GFB housing for increasing shaft speed from 5 krpm to 15 krpm with static load of 58.9 N (6 kgf ). Nominal radial clearance: 70 μm and 40 μm.

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Figure 6

Steady-state GFB housing temperature at bearing centerline (C) with increasing static loads of 58.9 N (6 kgf ), 78.5 N (8 kgf ), and 98.1 N (10 kgf ). Nominal radial clearances of 70 μm and 40 μm. Shaft speeds of 10 krpm and 15 krpm.

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