Micro Aerial Vehicles (MAV) require extremely lightweight propulsion systems. Whereas most current MAV use electric batteries as power sources, the presented work examines the possibility of using Phase-Change Materials (PCM) as part of an alternative propulsion system. The proposed power plant involves a rapid depressurization of cryogenic fluids from a stable liquid state to create vapor nuclei (bubbles), followed by nuclei growth till they coalesce, forming a continuous vapor phase which is heated by the surroundings and later drive a micro-turbine. The transformation rate from liquid to vapor plays a prominent role in the system, and the limiting transition rates of several materials are investigated in terms of their initial temperature and pressure, as well as of the dimensions of the orifice through which they exit.
A theoretical parametric analysis of these impacts will be thoroughly reviewed, introducing the homogeneous and heterogeneous nucleation rates (according to several theories) alongside the correlating depressurization rates necessary to achieve them; as well as demonstrating the applicability of such propulsion systems to propel a MAV by evaluating their outputs, such as specific energy, specific power, possible mission time and total mass. The system combinations that provide the minimal specifications will be exhibited, with a focus on Hydrogen and Neon – which were found to be the most promising substances per unit of mass and volume, respectively. Comparison with electric batteries will be presented.
