Origin of Knudsen forces on heated microbeams

The presented work probes the fundamentals of Knudsen forces. Using the direct simulation Monte Carlo (DSMC) method, the flows induced by temperature inhomogeneity within a representative configuration and the Knudsen force acting on a heated microbeam are captured as functions of Knudsen number in the entire flow regime. Both flow strength and Knudsen force peak in the transition regime and negative Knudsen force absent in experimental data is observed. The mechanisms of the thermally induced flows and Knudsen forces are studied. It has been found that thermal edge flow is the main driven source for the formation of the Knudsen force on microbeams and domain configuration plays an important role in the process.

Figure 1

Schematic illustration of the model problem.

Figure 2

Temperature contours for cases with $20\times 8\mu {\text{m}}^2$ chamber and $10\times 2\mu {\text{m}}^2$ beam: (a) $\text{Kn}=0.056$, (b) $\text{Kn}=1.1$, (c) $\text{Kn}=56$.

Figure 3

Knudsen forces versus Knudsen numbers.

Figure 4

(Color online) Flow structures throughout the domain (a) $\text{Kn}=0.11$, (b) $\text{Kn}=0.37$, (c) $\text{Kn}=1.1$, (d) $\text{Kn}=2.3$, (e) $\text{Kn}=56$.

Figure 5

(Color online) Schematic illustration of thermal edge flow (Contour lines and labels indicate the temperature distribution).