| The high frequency pulse tube cryocooler driven by the linear compressor and without moving part at the low temperature end of the cold finger,has evident advantages such as high reliability,long life,low vibration,comparing with Stirling cryocooler and GM cryocooler.Now the inertance-type pulse tube cryocooler is widely used in infrared detector.With the rapid developments of space technology in our country recently,the high efficiency pulse tube cryocoolers are in urgent needs.The pulse tube cryocooler uses the phase shift at the warm ends to achieve the required phase relationship between the mass flow and pressure wave.A better phase relationship can reduce the losses of the regenerator and enhance the efficiency of the pulse tube cryocooler apparently.Investigation on the phase shift is the key to improve the efficiency of the high frequency pulse tube cryocooler.In this study,we design an stirling type pulse tube cryocooler with an active phase control.And the pneumatic free warm piston is used as phase shift of pulse tube cryocooler based on the research of active phase control.The following three aspects are carried out in this paper.1 The theoretical analysis is carried out on the phase characterisrics of the high frequency pulse tube cryocooler.The energy flows in the pulse tube cryocooler are analyzed by the enthalpy flow theory,and the theoretical expression of the ideal cooling power is given.The theoretical research method of the phase characteristics is summarized based on the conservation of mass and energy.The common three phasor diagrams such as orifice-type,double-inet type and inertance-type pulse tube cryocoolers are constructed and compared.2 The numerical simulation and experimental research of stirling type pulse tube cryocooler with an active phase control is carried out.An electrically driven and mechanically damped linear compressor,which is directly connected at the warm end of the pulse tube by using a connecting tube,is used as the active phase controller(APC)instead of using inertance and buffer as a phasor.A stirling type active phase control pulse tube refrigerator is easy to control the electric input power and the displacement phase angle between APC and pressure wave generator(PWG),which helps control the phase angle between the mass flow and the pressure so as to make the pulse tube refrigerator to achieve its optimal performance.In this paper,we use one-dimensional software to simulate the stirling type pulse tube refrigerator with APC.And the stirling type pulse tube refrigerator with APC has been experimentally investigated.The study turns out when the electric input power is constant,the displacement phase angle between APC and PWG is 110 degree and the swept volume ratio(the PWG swept volume / the APC swept volume)is 2.98,the relative Carnot efficiency can reach highest.3 The phase shift design and experiment study on a pneumatic free warm piston pulse tube cryocooler(PTC)is carried out.We report a type of pulse tube cryocooler where pneumatic free warm piston instead of inertance and buffer,is used as a phasor.It can reduce the volume of the phasor and improve the performance of the PTC.The effects of the moving mass and spring stiffness and the area of piston on performance of the PTC are introduced based on numerical simulation.The experiment was shown the performance of refrigerator at different charge pressure and working frequency under constant input power.Experiment results indicate that when the the working frequency increases,displacement phase difference between compressor piston and pneumatic free warm piston(displacement phase difference)increases and the swept volume ratio of the compress piston over the pneumatic free warm piston(swept volume ratio)increases.The cooling power at 84 K was 7 W with an input electric power of 127 W and the relative Carnot efficiency is 14.25%,which improve 30% when compared to the stirling type pulse tube refrigerator with an inertance tube. |
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