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16.1 Status quo
This study has examined phenomena material to the performance of closed-cycle, regenerative cryo-coolers. Analytical and numerical techniques have been developed for quantifying the way in which the selected phenomena influence the gas processes. Emphasis has been on approaches that have received little exposure elsewhere.
In the case of the free-displacer Stirling cycle machine, one promising path to improved performance is clear: the potential of grading the regenerator matrix can be investigated in a regime of simulation (using the material of Chapter 5) and optimization (Chapter 9) in parallel with (essential) experimentation.
Any scope for improved regenerator performance is transferable in principle to the pulse-tube variant. However, the route to identifying the optimum in the latter case is not obvious. Whereas half a century of modern development of Stirling coolers has led to some sort of ‘feel’ for required phase angle, volume ratio, etc., nothing comparable exists to guide the choice of proportions for the pulse-tube.
Ideally one might probe the performance potential of the different design options (plain Gifford, orifice, inertance duct, etc.), using the full gamut of modelling techniques. To be credible, however, such a study would call for design specification of several machines of each type, together with respective performance data corresponding to the conditions of test (working fluid, charge pressure, cyclic frequency). ...