Liquid Piston Stirling Engines

Abstract

The Fluidyne liquid piston engine is a simple free-piston Stirling engine that can be made from nothing more than some lengths of tubing. The pistons are liquid, so they always fit the cylinder exactly with no need for machining, close tolerances, mechanical seals or bearings. On the other hand, the liquid piston engine in its simplest form operates at close to atmospheric pressure, and at a low frequency - typically 1/2 to 1 Hz. Consequently, the power density is low, and a large machine is needed if a substantial power output is required. These factors, along with the convenience with which a liquid piston machine can be adapted to pumping, have defined the main fields of potential application. Most interest so far has centered around the use of Fluidynes to pump water, particularly for irrigation or drainage pumping in developing countries or in more specialized circumstances where electric power may not be reliably available. However, as any other Stirling machine, the liquid piston engine can be operated as a refrigerator or heat pump and several workers have proposed exploiting this. Walker has suggested that a liquid helium cooler - for example, to service superconducting computers - could be made in which the liquid helium would be contained in a Fluidyne machine, driven by gas pressure variations from outside the cryogenic region. W. Martini has demonstrated that the liquid piston engine can be operated as a heat-actuated heat pump.

Dr. Colin West, Box 262A, Oliver Springs, Tenn. 37840, contributed this chapter on liquid piston Stirling engines — it gives the flavour of his recent more extensive work of the same title . Colin West worked at the British Government research establishment, the Atomic Energy Research Establishment, at Harwell under the supervision of Mr. E.H. Cooke-Yarborough (see Chapter 6) throughout the 1970 ’s. Among other projects he worked on the diaphragm Stirling engine described in Chapter 6, the Harwell TMG. It was during this time that Colin invented the liquid piston Stirling engine that has remained a prime interest source.

He now works at the U.S. Government Oak Ridge National Laboratory, Tennessee, and continues developmental studies of liquid piston Stirling engines in his spare time.

G. Walker