The Makings of a Micro-scale Steam Engine

by Simone Ferdinand, Nicholas Fuller, and Joshua Logan

Through previous experimentation on the micro-scale level, the powerful polar capabilities of water has been noted. Many devices that have been released have often been subjected to the strong pulling action of water, called stiction. Once micro machined objects such as cantilevers have been pulled to the substrate by this action, it is practically impossible to separate them without their destruction. Therefore, a micro machine designed to use these capabilities to the furthest extent would be advantageous.

Jeff Sniegouski and Paul McWhorter of Sandia National Laboratories are credited with creating the first microscopic steam engine. The micro actuator stands apart from other electrostatically driven micro actuators by its high torque and displacement. In tests, the engine piston was able to generate 1.16 ´┐ŻN of force, about 100 times the capability of a single electrostatic drive beam. Although there are obvious advantages in the development of this prototype, there are also drawbacks to the device. The designers had two main concerns:

1) The extensive time lapse between the initial thrust and retraction of the piston. (Compared with the powerful 0.1s thrust, the 1s waiting time for the steam to contract back into liquid form is inefficient.

2) The eventual evaporation of the expanding medium. We attempted to improve upon those things.

We decided upon two methods of reducing the time it takes the piston to retract. One way was to allow some way for the steam to escape from the chamber. We created steam release holes that were positioned so that when the piston traveled its furthest distance, the piston would reveal the release holes and steam would be able to leave the chamber.

A second method would be to provide a channel for the steam to travel. While going through the channel, the steam will come into contact with a cooling lattice designed to draw the heat from the steam and allow it to contract back into liquid to be reused.

To combat the eventual evaporation of the fluid, we attached a water reservoir to the steam engine. This will provide a constant supply of fluid that the steam engine would be able to use.