| Stirling/pulse tube hybrid cryocoolers(ST/PTCs)which combine the advantages of both Stirling cryocoolers and pulse tube cryocoolers have the potential to reach low cooling temperature efficiently,and those features make ST/PTC a very promising candidate for long duration deep space exploration mission's cooling system.However,the study of ST/PTC is very limited and the working mechanism and coupling characteristic between stages remain unknown at present.Based on the shortages in the study of working principles and coupling characteristic between stages,this thesis carries out the following work.1)Energy flow analysis and phase relation and of ST/PTCs based on the time-averaged thermodynamic method and phase shifting theoryEnergy flows of ST/PTCs are analyzed based on the time-averaged thermodynamic method,the results show that:ST/PTCs recovers the expansion work of the displacer,the maximum acoustic power in the ST/PTCs equals to the sum of the compression work and the cooling power of the Stirling stages,this result is different from the situation of pulse tube cryocoolers.The efficiency of the Stirling stage is verified based on the energy flows.Phase relations between pressure wave and mass flow are analyzed based on the phase shifting theory,the results indicate that:as a result of the interactions of displacer and expansion space,the phase angle between pressure wave and mass flows shifts from negative(mass flow lags pressure wave)at cold end of the displacer to positive at the inlet of the regenerator of the pulse tube stage.This phase shift guarantees the regenerators of both stages work in an optimum condition and makes the ST/PTC working efficiently.2)An idealized mathematical dynamic model of pneumatic driven Stirling cryocooler is establishedAn idealized mathematical dynamic model of pneumatic driven Stirling cryocooler is established based on some assumptions.The displacements of the displacer and piston are obtained by solving the dynamics equations of that component,the pressure is got by the mass conservation of the cryocooler.The whole picture of the phase relation between the displacements,pressure,and forces are established,and the expressions of cooling power,input power and COP are derived.The results reveal that proper phase relation between displacements and pressure at the expansion space of pneumatic driven Stirling cannot be achieved with the absence of damping force.The essential damping force would dissipate a fraction of acoustic power from the compression space,this dissipation leads to an intrinsic COP of pneumatic driven Stirling less the Carnot COP even with ideal regenerator and lossless compression and expansion.3)Coupling characteristic between stages of ST/PTCs are revealed theoretically and experimentallyA pneumatic driven ST/PTC is designed and tested,and a phenomenon of heating of the Stirling stage is found.The influence of the pulse tube stage on the Stirling stage is studied by introducing the impedance of pulse tube stage to the idealized mathematical model of pneumatic driven Stirling cryocoolers.Results indicate that the adding of the pulse tube stage would decrease the amplitude of the pressure and the phase angle between the pressure and the displacement of the displacer has a tendency of shifting from a negative phase angle to a positive phase angle.A positive phase angle between the pressure and the displacement of the displacer which produce heat would occur if the impedance of pulse tube stage is not well designed or the original phase angle of the Stirling stage is too small.Experiment results have a good coincidence with the theoretical analysis,it shows that the phase angle between the pressure and the displacement of the displacer changes from-16.0° to 17.3° for the home-made pneumatic driven ST/PTC,and the amplitude of the pressure decreases 22%compared with the origin Stirling cryocooler. |
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