Performance Investigation On Liquid-Helium Temperature Two-Stage Pulse Tube Cryocooler With ～3He/～4He As Working Fluid

No moving part existing in the cold part of a pulse tube cooler makes lower vibration, therefore higher reliability and lower electromagnetic noise level. The developments in phase shifting methods and magnetic regenerative materials have made great progress in pulse tube refrigeration. Up to now, the single-stage pulse tube cooler has become a competitive commercial refrigerator. And a minimum temperature of 2K or so could be achieved by liquid helium multi-stage pulse tube coolers with 4He as the working fluid, though the efficiency at 4.2K is still lower than that of G-M or Solvay cryocoolers. So far, the lowest no-load minimum temperature was 2.07K obtained by Thummes et al with a liquid nitrogen precooled two-stage pulse tube cryocooler using 4He as the working fluid. This current work is aimed at liquid helium temperature pulse tube refrigeration. Investigation on extending the refrigeration temperature limitation and improving performance in liquid helium temperature region by use of 3He as the working fluid of a pulse tube cooler is developed.For regenerative cryocoolers using 4He as the working fluid, a refrigeration temperature limit of 2K or so is induced by the X superfluid phase transition of 4He. The sharp increase of the fluid specific heat accompanying the superfluid phase transition makes regenerators disabled. Besides, the thermal expansion coefficient ap of 4He also equals zero around 2K, which means no temperature changes caused by adiabatic compression or expansion, so no refrigeration produced by pulse tube coolers. So researchers have tried to break the temperature barrier of 4He by using 3He, whose superfluid phase transition occurs in the mK temperature region and thermal expansion coefficient approaches zero around IK. A minimum no-load temperature of 1.47K with 3He was obtained by a two-stage GM cooler. And by a three-stage pulse tube cryocooler, a minimum no-load temperature of 1.78K with 3He was achieved by Eindhoven group.The properties of the isotope He-3 differ considerably from those of He-4 at low temperatures because of quantum effects. Thermodynamic properties of cryogenic fluids areinvolved in many fields of cryogenic engineering. So extensive and accurate property data make the base of cryogenic system designs. So far the properties of many common fluids could be obtained by state equations, calculation models and software, except helium-3. On one hand, there are not sufficient property data about helium-3. On the other hand, the data collective work of it was seldom developed. So in this paper firstly the thermodynamic properties of helium-3 needed by the design of cryogenic systems using helium-3 as the working fluid were collected. And based on the work of Gibbons etc., using a modified Strobridge equation and a modified quantum version of the principle of corresponding states,a computer program--He-3 Pack--was built which could calculate the properties ofHe-3 between 1 and 100 K, up to 10MPa, including the PVT properties, entropy, enthalpy, internal energy, thermal conductivity and viscosity. The calculation results obtained by He-3 Pack agree with the technical report AFML-TR-67-175 from Air Products and Chemical Inc. to Air Force Materials Laboratory. The relative error of the PVT properties and entropy is less than 2% and that of the enthalpy is within 8%. The accuracy of the database could be improved in our future work.In order to make full use of the advantage of single-stage pulse tube coolers and develop the research using 3He as the working fluid to break the refrigeration temperature limitation of regenerative cryocoolers induced by X superfluid phase transition of 4He, a newly-designed two-stage pulse tube cooler consisting of two separate single-stage pulse tubes was built. This feature makes it possible to run only the 2nd stage with either 4He or expensive 3He working fluid. And in comparison with the conventional 4 K PTCs with common gas supply, the interdependence of the two stages appears to be significantly smaller in the present cooler. To save the amount o...