Numerical simulations of Knudsen forces in microsystems
Abstract
At the microscale, even moderate temperature differences can result in significant Knudsen forces, generated by the energy exchange between gas molecules and solids immersed in a gas. Creating, controlling and measuring Knudsen forces precisely at the microscale can be an arduous task since only limited theory exists at present. Moreover, the widely used continuum-based thermofluid simulation tools, such as FLUENT by ANSYS, are not able to predict the Knudsen forces. Here subcontinuum simulations are developed in order to provide a basis for understanding the physical mechanisms governing the generation of Knudsen forces. The first part of the present study investigates the mechanism of Knudsen forces in detail based on numerical solution of the Boltzmann kinetic equation. The Knudsen force is shown, in general, to be a result of thermal non-equilibrium between gas and solid. The simulations are verified by comparison with experimental measurements that have been reported by Passian et al. [2] using heated atomic force microscope probes. A closed-form model for the Knudsen force on a beam is obtained based on the simulations and can be applied for analysis and design of microsystems. The second part of the study focuses on the application of the compact model in the design of a sensor. The unsteady beam equation is numerically solved to predict the deflection and switching time of the fixed-fixed beam and free-end beam configurations.
Degree
M.S.A.A.
Advisors
Alexeenko, Purdue University.
Subject Area
Aerospace engineering|Mechanical engineering
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