Solar energy conversion with thermal cycles - Solar Energy Sciences and Engineering Applications - page 471

Linear alternator Stirling engine

Regenerator

Rear flexure
stack

Front flexure
stack

Mover Piston Displacer

Figure 14.5.8 Schematic representation of a Beta free-piston Stirling generator.

Figure 14.5.9 Double-effect Alpha configuration.

inertial effects due to the presence of three or four pistons, respectively phase-shifted
by 120 ◦ or 90 ◦ , which improve mechanical efficiency since the dual action works the
crank in one direction while compression is directly subtracted from expansion.

14.5.5 Stirling working fluids
The working fluid in a Stirling engine is employed in a closed cycle and has to sat-
isfy the following requirements: (i) good heat transfer coefficients; (ii) low viscosity;
(iii) high thermal stability; and possibly (iv) low cost (Urieli and Berchowitz, 1984).
Light molecule fluids like H 2 or He are considered suitable fluids for solar dish
Stirling applications because they meet the majority of these requirements; however, a
small caveat concerns leakages. In fact, due to the small size of their molecules, these
fluids tend to escape through seals. The problem is more serious for H 2 because of