| Modern technology calls increasingly for provision of cooling at cryogenic temperatures: super-conductivity research; imaging equipment for search-and-rescue; contemporary diagnostic medicine (MRI – magnetic resonance imaging); space exploration; advanced computer hardware; military defence systems. Where is desirable to generate the cooling effect close to the point of heat removal, electrically powered Stirling and pulse-tube machines offer advantages over traditional, passive systems (Leidenfrost and Joule-Thomson). The Stirling has the greater number of moving parts, but operates on a straightforward gas processes cycle. The pulse-tube dispenses with the displacer, exploiting instead a lack of equilibrium in the gas processes to provoke internal enthalpy migration and thus cooling. However, the kinematic simplicity of the pulse-tube is achieved at the cost of inscrutability of the gas process cycle.
To date there has been no agreed approach to the thermodynamic design of either type. In particular, the choice of regenerator packing has remained a matter for time-consuming – and thus expensive – trial-and-error development. There has been no way of knowing whether an existing ‘fully developed’ unit is performing to the limit of its thermodynamic potential. Stirling and Pulse-tube Cryo-coolers addresses these problems. Re-cycling of known material is held to a minimum in favour of an original approach, which will not be found elsewhere. Development proceeds by graphic visualization of the gas processes explored, but above all by following unifying themes: a gas dynamics handling flow modelling real gas behaviour via incorporation of van der Waals’ equation of state. No opportunity is missed to exploit the power of dynamic similarity. Features include: *An ideal cycle for the pulse-tube yielding heat, mass-flow and work; *Previously unseen phenomena of real gas behaviour; *Pictorial reliefs of pressure wave interactions; *Multiple wave reflections in graphic perspective *First solution of the ‘regenerator problem ‘ by a full, unsteady gas dynamics treatment; *First ever depiction of pulse-tube boundary-layer events (heat conduction, ‘streaming’) driven by interacting left-and right-running pressure waves *First analysis of the graded regenerator and optimisation of gas path design; *Embryonic ‘cook-book’ method of ab initio cooler design based on dynamic similarity and thermodynamic scaling. Stirling and Pulse-tube Cryo-coolers raises the threshold from which first-principles design of regenerative cryo-coolers may start. Those wishing to extend their study of the subject beyond the well-trodden, ideal gas/quasi-steady-state rationalisations will require this book.
|
