The thermodynamic performance of a Stirling cryocooler is closely linked to the movements of the two reciprocating components i.e. the compressor piston and displacer. In mechanically constrained units, such as crank-driven models or those with a rhombic drive, performance prediction is simplified by the fact that strokes of the piston and the displacer are fully determined by the geometry of the machines, and so is the phase difference between them. Hence, these are unaffected by the machine speed and gas pressure in the spaces and are thus constant in the analysis. However free piston free displacer units, since the reciprocating parts are constrained only by mechanical springs, the analysis is much more complicated. A number of dynamic and Thermodynamic variables exist which are mutually dependent i.e. strokes, pressures, temperatures and phase shift. Some researchers have coupled the thermodynamics and dynamics giving real picture of the processes. The thermodynamic processes have been assumed to be isothermal in their models. In the present paper the performance parameters have been evaluated by assuming the real processes.
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