Thermodynamic Characteristics Of The Stirling/ Pulse Tube Hybrid Cryocooler And Its Experimental Verification

The Stirling/pulse tube hybrid cryocooler is comprised of the Stirling cryocooler as the first stage and the pulse tube cryocooler as the second stage,and the two stages are gascoupled.Such a structure allows each stage to operate under the proper working condition of its own,making full use of the advantages of each stage while mitigating their disadvantages.Moreover,the cooling capacity of the hybrid cryocooler can be redistributed between stages by adjusting the movement of the displacer in the first stage,and the timevarying heat loads at both stages can therefore be satisfied.Therefore,the hybrid cryocooler shows great potencial in cooling the space detectors.However,the existing analytical models and open literatures can hardly be applied to analyze the hybrid cryocooler's thermodynamic characteristics as well as make a design,which has limited the development of the hybrid cryocooler.To address this problem,the following subjects are studied.1.Establish the general model of the Stirling-type cryocooler based on the transmission line equation As the theoretical models of the Stirling cryocooler and the pulse tube cryocooler are established based on various theory systems at present,a general model of the Stirling-type cryocooler is established based on the transmission line equation.This model includes the pressure equation and the volume equation.The pressure equation describes the relation between the pressure at various locations and the volume change of the chambers,while the volume equation describes the relation between the volume changer of the chambers and the moving parts of a specific type of the Stirling-type cryocooler.As an analytical model that takes account of the acoustic resistance,the acoustic compliance and the acoustic inductance,the general model can describe the realistic situation in a relatively accurate manner as well as explicitly express the relation between the parameters.2.Establish the theoretical model of the hybrid cryocooler and study its thermodynamic characteristics Based on the general model,the theoretical model of the hybrid cryocooelr is established.The theoretical model indicates the phasor relation between the pressure and the displacement of the moving parts as well as gives the expression of the cooling capacity at both stages.Using the motor-driven displacer Stirling/pulse tube cryocooler as an example,the thermodynamic characteristics of the hybrid cryocooelr is analyzed,including the condition that enables the first stage to produce cooling and the basic law of interstage cooling capacity redistribution.3.Improve the design method of the hybrid cryocooler Based on the thermodynamic characteristics and the related criterion of the hybrid cryocooler,the design method of the hybrid cryocooler is improved.A range of phase difference and swept volume ratio between the piston and the displacer is given by the criterion.Such a range allows the hybrid cryocooler to make full use of its thermodynamic advantages.This improved method makes the design more reasonable and effective.4.Verify the model and the related theories by experiment A prototype machine of the hybrid cryocooler is designed.With the prototype machine,three sets of experiment are performed.The single-stage Stirling cryocooler experiment quantitively verifies the general model of the Stirling-type cryocooler and provides the data for comparison in the following sets of experiment.The hybrid cryocooler experiment with precooling qualitatively verifies the features of the pressure,the condition that the hybrid cryocooler is able to redistribute cooling capacity between stages and the related laws.The hybrid cryocooler experiment without precooling qualitatively verifies that the first stage may produce heat or cooling.