Development of a Portable Pneumatic Power Source Using Phase Transition at the Triple Point

Abstract

This study is concerned with the development of a novel portable pneumatic power source applicable to mobile applications such as wearable actuator and rescue robot etc. The dry-ice, which is the solid phase of the carbon dioxide, is chosen as the source of the power for the developed power source because it is nonpoisonous, easy to obtain, low in price and it expands 750 times in volume after being vaporized into the gas. When dry-ice is stored in the confined pressure container, the pressure and temperature rise by heat transfer and it begins to liquefy after the pressure and temperature reach the triple point (0.52 [MPa (abs)] , -56°C). In this process the pressure remains constant until all the dry-ice melts into the liquid. When the state remains at triple point, the pressure does not decrease even though the gas is released from the pressure container. Accordingly, this means that the state can be used as a stable pneumatic power source. By using this physical property of carbon dioxide at the triple point, and by controlling the heat transfer from the surroundings into the pressure container, a noiseless, large capacity, light and portable pneumatic power source is developed. In this paper, the structure and the flow characteristic of the pneumatic power source is described in detail.