Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : September 08, 2019 - September 11, 2019
In rarefied gas flow conditions, where the length scale of the flow is comparable with the mean free path of the gas, a Knudsen thermal force can be induced. This force can be generated on a structure immersed in a gas in the presence of thermal gradients1. Such phenomenon is significant for vacuum microbalances as well as for microsystem sensors and actuators. The mechanisms governing this force show strong dependence on the nature of thermal gradients within the system1. It has been studied that in the case of a heated micro-beam placed on cold flat surface, a repulsive force is exerted on the micro-beam2. Furthermore, it was also investigated that when a cold object is placed over a heated micro-ratchet surface, a propulsive force is exerted on the object. This combination of repulsive and propulsive force is the interest of this study. While measuring such forces precisely at microscale can be an arduous task, numerical simulations can provide a basis for understanding the physical mechanisms of such forces. Moreover, such forces do not occur in the continuum flow regime, and hence, the Navier-Stokes equation cannot be used, and instead, the more general Boltzmann equation is required which can be numerically solved using the direct simulation Monte Carlo (DSMC) method. The main goal of this paper is to determine the forces exerted on a uniformly heated micro-beam placed at a distance away from a cold micro-ratchet surface using DSMC simulation. Figure 1 shows that the asymmetric shape of the ratchet induces a strong non-uniform temperature distribution, which in turn, induces thermally driven flows. The strongest flows are seen in the vicinity of the ratchet tip and the corners of the solid beam.
