Phase change material engine for micro air vehicle - Design and process analysis

In the past several years as the use of unmanned flying vehicles has increased dramatically, miniaturization has become a main line of developing systems. As vehicles have become smaller and smaller, the demand for energy and power has made the energy source and system a limiting factor by its size and weight and conventional systems such as internal combustion engines [1] and battery operated electrical motors are cutting it close to meet the specific energy and power requirements for a miniature vehicle. Lidor et al. [2] examined several energy source alternatives, including springs, flywheels, thermonuclear micro devices, artificial muscles, carbon nano-tubes, pneumatic systems, fuel cells and phase changing materials (PCM) based systems. This study focuses on the process of a proposed solution on one of the promising alternatives - the PCM based engine. The design is an open system, containing an insulated pressure tank holding the cryogenic fluid, a series of heat exchangers and a turbine. The design uses the heated working fluid itself to bring heat from the environment to the cold liquid in the tank in a controlled coupled fashion in order to sustain boiling. This paper covers analytical study of the process, evaluates its stability and offers manners of controlling and regulating it. Finally, empiric results from a test bench are brought, proving the concept and showing an actual PCM engine performance.