Key Components And Overall Performance Study Of The Moving-Magnet Linear Compressor For Striling Refrigerator With Large Cooling Capacity

With the rapid technical improvement of aero scope, solid electronics and cryobiology, free-piston, high cooling capacity Stirling refrigerators based on the moving magnet linear compressor own bright and extensive application prospect. In this paper, the performances of the key components of moving magnet linear compressor and compressor itself have been studied experimentally and theoretically respectively. As a result, the first prototype of moving magnet linear compressor has been manufactured successfully. Generally speaking, the investigation of this paper is composed of coupled three parts, such as the investigation of flexure spring, dynamic and static characteristic study of moving magnet linear motor and the comprehensive performance study of linear compressor and refrigerator.Firstly, the design theory of spiral flexure spring has been given in this paper, in which the spiral profile has been described precisely by the geometrical equations. The smooth transitions between different curves avoid the stress concentration effectively. The theoretical mathematical model based on the infinitesimal force equilibrium equation has been set up and then solved by virtue of integration along with the spiral profile. The expression of axial stiffness has been deduced. By the same way, the dynamic equation of spiral arms has been set up and solve, the natural frequency has been expressed as the function of geometrical boundary. In order to validate the above theory, the finite element and experiment study has also been conducted respectively. On the one side, the performance of eleven different spiral springs on the basis of the finite element analysis have been compared with that of theoretical solution; on the other side, the TSL series stiffness meter has also been used to get the stiffness of single spring and their assembly. In addition, the torque characteristic has also been revealed at first time.Secondly, the investigation of moving magnet emphasizes on the static and dynamic characteristic of electromagnetic force. After determining the design method of electrical and magnetic circuit, based on the Maxwell equations, the mathematical model of magnet circuit has been set up. As the solution of this model, the expression of electro magnetic force reveals its attenuation characteristic with the increase of displacement and meanwhile provides effective information to alleviate this characteristic. The finite element model has also been set up to get the distribution characteristics of magnet field, which has close relationship with the electromagnetic force. In order to validate the theoretical results, the static force measuring apparatuses has been built, by which following three aspects investigations have been done, relation between current and force, relation between force and displacement and steady characteristic of mover. It is found that although there have the positive correlation between the current and force, the force along the stroke is not constant, which is the important characteristic of moving magnet linear motor. The theoretical results agree with the experimental data well. The equilibrium characteristic of mover discovered in the experimental study reveals that there exist one unsteady and two steady equilibrium points. The theoretical solution of force can explain this phenomenon and predict the position of these points. So it is the foundation of optimizing design.Finally, the theoretical and experimental study of overall performance of moving magnet linear compressor has been conducted respectively. In combination with the above spring and motor sub models, the mathematical model of compressor has been set up on the basis of dynamic and thermodynamic analysis. The thermodynamic equations mainly describe the gas thermodynamic process including compression, expansion and leakage. The corresponding differential equations have been set up and solved respectively. The dynamic study mainly focuses on the force balance of mover and voltage balance of driving circuit. Numerical integration has been used to solve this nonlinear equation. Furthermore, the equivalent energy method has been used to linearize those nonlinear equations, so the harmonic and matrix solution can be deduced, on the basis of which, the mechanical-electrical simulating model is obtained. In addition, in order to analyze the steady criterion, stroke-voltage and frequency characteristic, Hurwitz theorem, time domain and frequency domain analysis has been applied to the linear model respectively. Using these analyses, the corresponding performance of compressor can be predicted.The experimental study of moving magnet linear compressor and Stirling refrigerator involves the construction of compressor, refrigerator and subsequent performance measure. Different from moving coil linear motor, the special key points including design process, manufacture technology and large current driving circuit has been presented. By means of varying the operation and geometry parameters of linear compressor including working frequency, voltage, current, charging pressure, mass of mover and clearance, the overall performance of linear compressor has been obtained. By comparison with the experimental study, theoretical model can predict the performance variation very well. It is found that light piston, high charging pressure and high working frequency will bring up large output power; optimal working frequency should be at the range of 85%-90% natural frequency; As for efficiency, the clearance should be as little as possible. But the heat expansion and machining technology should also been considered.The prototype of Stirling refrigerator has been formed by integrating linear compressor with pneumatic expander. The optimal operating points have been found by varying the charging pressure, frequency and input power, the maximum performance is 200K@36W.