A micro fin rotational mechanism: Non-equilibrium rarefied gas flow and radiometric torque by a temperature field

Non-uniform temperature fields can trigger thermally induced flows, generating radiometric force and radiometric torque on the solid structure. Thus, rotational motion occurs. The non-equilibrium gas flows of the microbeam with equilateral triangle fin surfaces immersed in the circular cold chamber are numerically investigated based on direct simulation Monte Carlo (DSMC) method. Here, one side of the equilateral triangle fin is cold, and the other side is hot. The characteristics of torque applied to the microbeam are analyzed for different configurations. Moreover, the output power and thermal efficiency performance are evaluated with the system as a heat engine model. It is demonstrated that the radiometric torque is a bell-shaped function of Knudsen number ( Kn ), reaching the peak value at around Kn ∼ 0.1 . The radiometric torque is almost a linear function of temperature difference, increasing monotonically with the temperature difference. However, the radiometric torque is inversely proportional to the chamber size, with a non-linear dependence. Moreover, the total torque is a linear function of rotational speed, monotonically decreasing with the rotational speed, which reveals its potential application for rotating machines. In addition, the dependence of output power on the rotational speed exhibits a parabolic profile. Both the maximum output power and the corresponding thermal efficiency have a non-linear dependence on Kn , and reach the peak values of ∼ 0.43 mW and ∼ 0.36 %, at Kn ∼ 0.2 and Kn ∼ 0.5 , respectively.