Development and testing of a novel 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 wearable robots, pneumatically operated tools, and other pneumatic devices. Dry ice was chosen as the source of power because it is non-poisonous, inexpensive, and it expands to 750 times its volume after it sublimes into gas. When dry ice fills a confined pressure container, it sublimes and then liquefies after the pressure reaches the triple point of CO 2 (0.52 MPa (abs), −56.6 °C). As long as dry ice remains at the triple point state in which all three phases coexist in equilibrium, the pressure remains constant and does not decrease even though the gas is released at a high rate of flow. In this study, by controlling the heat transfer between the pressure container and the ambient atmosphere, a novel pneumatic power source, which always stores dry ice in a state near its triple point, was developed. It has a constant output pressure of 0.42 MPa and is quiet, light, and safe, and produces a large capacity of pneumatic flow. Most significantly, the device does not require a large amount of operation power because it uses saved latent heat.