An analytical model of a silicon MEMS vaporizing liquid microthruster and some experimental studies

A recent application of the MEMS technology is in the field of microthrusters for micro/nano satellites. A silicon MEMS vaporizing liquid microthruster (VLM) produces continuously variable thrust in the range from μN to mN. The theoretical simulation of a VLM involves complex numerical 3D micro-fluidic, thermodynamic and electro-thermal solutions. A fast analytical method is, however, desirable in the initial phase of development of a VLM. In this paper, a simple analytical model of a VLM is presented. The model is based on one-dimensional approximations for fluid-dynamical and heat-flow equations. VLMs are fabricated by bonding two micromachined silicon chips. The device consists of a microcavity, an inlet nozzle, an exit nozzle, a microchannel and an internal p-diffused resistor for heating. The thrust is measured by a sensitive cantilever and a laser based lamp-and-scale arrangement. The experimental results on the variation of thrust with heater power are interpreted with the help of the theoretical model. A novel iterative computation is performed to extract the chamber temperature and other important parameters corresponding to the measured values of thrust for different values of heater power. The model gives some physical insight into the operation of the VLM.