Fundamental study on laser opto-microactuator under molecular gas dynamics conditions

The application areas of the molecular gas dynamics besides aeronautics and astronautics include some frontier realms of the advanced technical development such as: plasma material processing in vacuum, micro-electronic etching, micro-electronic mechanic systems and chemical industry. When the density is lowered to a level that the mean free path of the gas molecules is not a small magnitude in comparison with the characteristic length of the flow, the ordinary methods of the continuum gas dynamics are no longer suitable, the methods of discrete molecular gas dynamics are required. A numerical analysis method was developed to simulate the molecular motion of rarefied gases. In the present study, numerical approaches by the Direct Simulation Monte Carlo (DSMC) method have been carried out. A laser opto-microactuator has been proposed as an optical-micro-electro-mechanical-systems. The energy supply to the micromachine should be wireless. A large temperature difference between the rotor surfaces of the laser opto-microactuator can induce the rotation of the rotor by the molecular gas dynamics effects. In order to proving a non-wiring type of energy supplying method, an energy absorption film has been studied for improving the rotational characteristics of the laser beam microactuator. The characteristics of the energy absorption film were appraised by the DSMC method. Taking into account the existing symmetries of the vacuum deposition machine, the flows inside the vacuum chamber were analyzed in a three-dimensional computational domain. In the computational model, air and carbon molecules are working ones. The effects of the air gas pressure variation in the chamber, the effects of the deposition distance variation and the surface temperature variation of the carbon fiber on thermo fluids phenomena are discussed and visualized. Comparison between experimental results and numerical results is carried out. The numerical results agree with the experimental data qualitatively. The results of the numerical analysis at the surface temperature of the carbon fiber at 1000 K approach to the experimental results. Moreover the deposited masses at the experimental results less than those at approach to actually deposited temperature of the carbon fiber surface 1500 K. In the propriety deposition distance, decreasing the air gas pressure in the chamber, the amount of deposition increases. The experimental conditions of the vacuum deposition are proposed. To simulate a rotating configuration the standard DSMC method must be modified significantly. This simulation is carried out in a rotating coordinate system fixed to the blade system. Thus the particle motion and the boundary conditions are to be transformed with respect to the rotating coordinate system. Here numerical approaches to the laser opto-microactuator by the DSMC method with multi-time steps are proposed. The proposed prediction-correction procedure can be used as a universal tool together with the standard DSMC method for simulation of gas flows with widely separated kinetic relaxation and macroscopic evolution time scales. The computational model of the DSMC method and boundary condition are described. Effects of the temperature differences, the blade size and the vertical position on the rotational characteristics are discussed and visualized. The rotational rates depend on the temperature differences between the blade front and rear surfaces, the blade size and the vertical positions in the case of the vertical blades. In the intermediate region of molecular gas dynamics, the actuator is a small fluid machinery rotated by the molecular gas dynamics effect with the energy conversion from laser beam energy to thermal energy. In the experiment, a suspension type of the actuator is proposed. The measurement method of the rotational rate of the laser opto-microactuator is introduced. Moreover the variation of rotational characteristics by the difference of the holding type of the axis, the rotor material and the surface temperature of the rotor with the laser irradiation are clarified. The holding type of the actuator axis was changed to a permanent magnet. Aluminum and glass were selected for the rotor materials. By the permanent magnet bearing and glass rotor the rotational rates of the rotor are faster than the rate of the aluminum rotor by 2.5 times. The rotational rate is experimentally measured and compared with the numerical results by DSMC. The increment of the calculated rotational rate within the transient period from a zero rotational rate to a steady rotation corresponds to experimental observations but the simulated rotational rates at the steady state over predicts more than those of the experiments by about twice.