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Ultralow friction in a superconducting magnetic bearing
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Siegel, Michael Laschuetza, Helmut Zaitsev, Oleg Bareiss, Martin Bornemann, Hans J. |
| Copyright Year | 1996 |
| Description | Passive levitation by superconducting magnetic bearings can be utilized in flywheels for energy storage. Basic design criteria of such a bearing are high levitation force, sufficient vertical and horizontal stability and low friction. A test facility was built for the measurement and evaluation of friction in a superconducting magnetic bearing as a function of operating temperature and pressure in the vacuum vessel. The bearing consists of a commercial disk shaped magnet levitated above single grain, melt-textured YBCO high-temperature superconductor material. The superconductor was conduction cooled by an integrated AEG tactical cryocooler. The temperature could be varied from 50 K to 80 K. The pressure in the vacuum chamber was varied from 1 bar to 10(exp -5) mbar. At the lowest pressure setting, the drag torque shows a linear frequency dependence over the entire range investigated (0 less than f less than 40 Hz). Magnetic friction, the frequency independent contribution, is very low. The frequency dependent drag torque is generated by molecular friction from molecule-surface collisions and by eddy currents. Given the specific geometry of the set-up and gas pressure, the molecular drag torque can be estimated. At a speed of 40 Hz, the coefficient of friction (drag-to-lift ratio) was measured to be mu = 1.6 x 10(exp -7) at 10(exp -5) mbar and T = 60 K. This is equivalent to a drag torque of 7.6 x 10(exp -10) Nm. Magnetic friction causes approx. 1% of the total losses. Molecular friction accounts for about 13% of the frequency dependent drag torque, the remaining 87% being due to eddy currents and losses from rotor unbalance. The specific energy loss is only 0.3% per hour. |
| File Size | 361645 |
| Page Count | 10 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19960052921 |
| Archival Resource Key | ark:/13960/t9s22x21d |
| Language | English |
| Publisher Date | 1996-07-01 |
| Access Restriction | Open |
| Subject Keyword | Mechanical Engineering Torque Magnetic Dipoles Vacuum Chambers Lift Drag Ratio Friction Drag Cryogenic Cooling Levitation Superconducting Magnets Friction Measurement Flywheels Magnetic Bearings Pressure Dependence Ybco Superconductors Coefficient of Friction Friction Drag Energy Dissipation Eddy Currents Energy Storage Operating Temperature Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
