Theoretical And Experimental Study On A Moving Coil Linear Compressor With Triangle Flexure Bearings

Cryocoolers have significant applications in many fields, such as aerospace, military, low temperature electronics, cold medicine, weather reports, and gas liquefaction areas. These applications make stringent demands for the reliability, low vibration and long life working time of the cryocooler. The linear compressor driving cryocooler adopts flexure bearings and clearance seal to maintain the non-contact reciprocating motion, which thoroughly eradicates the wear between the cylinder and piston. Because of its advantages of stability, little vibration, low noise, electric power conversion efficiency and long life, lienar compressor is the ideal driving source for the above applications. In addition, the lienar compressor technology could also be used for the refrigerator as the global trend of energy saving.Owing to these advantages of linear compressor, this paper reports the first self-made moving coil linear compressor with triangle flexure bearings in our nation. The theoretical calculation methods, the simulation optimizing approaches, and some experiments are illustrated as follows:1. The electrical and dynamic theory of linear compressorThis paper summarizes the basic design process of a linear compressor, and adopts the complex transition to calculate the structure parameters including the diameter of the piston, the PV power provided by the compressor. The moving coil linear motor was constructed by the electrical theory and some basical parameters of the linear motor, such as the length of the return iron, and the depth of the gap are demonstrated by the formulars.2. Numerical analysis of key components of linear compressorThe finite element method (FEM) is employed to simulate the interior magnetic flux of the linear motor. Aiming to get an optimized structure for the linear motor, a number of different structures were constructed and calculated by FEM process. From these analysises, a single linear motor that could produce magnetic force of 231.7N, when the exciting current is about 7A, is constructed by this simulation. Three different types of flexure bearings, which are concentric spiral flexure bearings, eccentric spiral flexure bearings and trangle flexure bearings, are compared through FEM calculation. The simulation results show that the trangle flexure bearings could generate the highest radical/axial stiffness ratio, and provide the largest natural frequency for the high frequency miniature linear compressor. Finally, the computational fluid design (CFD) software "Fluent" is introduced to describe the detail fluid mechanism in the clearance. The linear clearance, which is smaller than 0.034mm, is used to minimize the clearance seal loss.3. The experimental work of the linear compressorIn order to prove the results of numerical calculation, the stiffness test of spiral flexure bearings are complete by the tension meter. As to the triangle flexure bearings, the axial stiffness from the experiment is 1.43N/mm and 1.47N/mm for the FEM simulation. The nature frequency of the spiral flexure bearings are also tested through the vibration experiments. The nature frequency of single flexure bearing is 25Hz and 135Hz of the flexure bearings group consisting of 5 pieces of bearings.The RC load method is employed to determine the efficiency of the linear compressor. From this experiment, we find that the resonant frequency of this self-made compressor is 25-30Hz, and it could produce the 89W PV power if the electricity power input is 150W, with 60% efficiency. This compressor could drive the pulse tube down to 49.1K, with 1.3 pressure ratio at the inlet of regernerator. Its working frequency is 40Hz and the electricity power input is 540W.