Computational study on vaporizing liquid micro-thruster

Simulation results showed that the models which consist of the pillar array structure induced more droplet collisions than those models constructed by the circle block, semi-circle block, ellipsoid block, and bevel fins, and avoided the deflection of the droplets which was revealed in the serpentine model. In addition, within the VLM chip, the wall temperature was much higher than the fluid temperature and certainly higher than those of the droplets in the flow due to the saturation temperature of fluid. Therefore, the more collisions occurred, the higher the droplet temperature was, due to the high heat flux caused by conduction between the droplets and the wall. Also, the longer flying durations of the droplets caused by the collisions increased the droplet temperature. The high droplet temperature implied the increase of the evaporation rate in the real VLM chip. Furthermore, the design with the pillar array structure provided a well axial thrust due to the symmetric trajectories of the droplets. From the viewpoint of the propellant efficiency and the properties of the ejected plume, the model with the pillar array structure is the best design pattern in the present study. In addition, the optimum pillar spacing should be 250 μm (center-to-center distances between two lines of pillar) in this work.