A Study of A Study of Lubricating Flows Lubricating Flows in MEMS Bearingsin MEMS Bearings

J. StreeterJ. Streeter11 E. Gutierez-Miravete E. Gutierez-Miravete22

11OptiwindOptiwind22Rensselaer at HartfordRensselaer at HartfordCOMSOL09COMSOL09

EFAB Manufacturing EFAB Manufacturing ProcessProcess

First Structural Layer Completed First Layer Completed Bearing Surface

Un-etched Assembly Etched Assembly Sample Assembly

Governing EquationsGoverning Equations

Mass Conservation (Continuity)Mass Conservation (Continuity)

div V = 0div V = 0

Momentum Conservation (Navier-Stokes)Momentum Conservation (Navier-Stokes)

V grad V = V grad V = div grad V - grad p + div grad V - grad p + g g

Journal BearingJournal Bearing

0 Offset 30 Offset 45 Offset

The journal bearing produces the same pressure differential regardless of the shaft offset.

Channel BearingChannel Bearing

4-Lobe 0 Offset 4-Lobe 45 Offset

6-Lobe 0 Offset 6-Lobe 30 Offset

Diffuser BearingDiffuser Bearing

4-Lobe 0 Offset 4-Lobe 45 Offset

6-Lobe 0 Offset 6-Lobe 30 Offset

Nozzle BearingNozzle Bearing

4-Lobe 0 Offset 4-Lobe 45 Offset

6-Lobe 0 Offset 6-Lobe 30 Offset

Computed Pressure Computed Pressure DifferentialsDifferentialsConfigurationConfiguration Nominal (Pa)Nominal (Pa) Offset (Pa)Offset (Pa)

JournalJournal 3.026 (1.00)3.026 (1.00) 3.023 (1.00)3.023 (1.00)

4-Lobe Channel4-Lobe Channel 2.493 (.824)2.493 (.824) 1.440 (.476)1.440 (.476)

6-Lobe Channel6-Lobe Channel 2.785 (.920)2.785 (.920) 1.758 (.582)1.758 (.582)

4-Lobe Diffuser4-Lobe Diffuser 2.427 (.802)2.427 (.802) 1.376 (.455)1.376 (.455)

6-Lobe Diffuser6-Lobe Diffuser 2.624 (.867)2.624 (.867) 1.666 (.551)1.666 (.551)

4-Lobe Nozzle4-Lobe Nozzle 2.573 (.850)2.573 (.850) 1.508 (.499)1.508 (.499)

6-Lobe Nozzle6-Lobe Nozzle 2.833 (.936)2.833 (.936) 1.788 (.591)1.788 (.591)

ConclusionsConclusions

This study has demonstrated that COMSOL This study has demonstrated that COMSOL can be used to demonstrate the hydrodynamic can be used to demonstrate the hydrodynamic performance of proposed MEMS designs.performance of proposed MEMS designs.

Specific features of bearing design determine Specific features of bearing design determine the resulting flow field and pressure distribution the resulting flow field and pressure distribution in the hydrodynamic gap.in the hydrodynamic gap.

Significant peak pressure reductions are Significant peak pressure reductions are possible by using multiple lobe diffuser-type possible by using multiple lobe diffuser-type MEMS configurationsMEMS configurations

Questions?Questions?