Research on Scroll Compressors with Variable Compression Ratio
|關鍵字:||渦卷;壓縮機;可變壓縮比;最佳化;scroll;compressor;variable compression ratio;optimization|
A scroll-type compressor (STC) with variable compression ratio using a variable-speed motor has become a major trend in recent years because of the requirements for variable capacities in high efficient refrigeration and air-conditioning systems. This study first develops a bypass valves mechanism which is disposed to the backside of a fixed scroll of STC. The over-compression resulted from the mismatch between the intrinsic volume ratio (the designed compression ratio) in STC and the variable operating pressure ratio (variable capacity) can be prevented by using this mechanism. In addition, this mechanism can also avoid the liquid slug while the refrigerant flows into the chamber of STC without enough superheat for fully vaporized. The mathematical model for the bypass valves has been constructed and integrated into a STC simulation computer package, and the high and low side structures of STC are also simulated respectively. Simulation results find that the subtle disposition of bypass valves can prevent the over-compression and liquid slug problems regardless various operating conditions. One practical STC product, with bypass valves built in it, has also validated the effect through the actual STC efficiency experiments. In addition, an optimization module had been combined into the simulation package for aiding the design of STC with variable capacities and speeds. One application regarding reducing frictional losses in bearing components of STC is demonstrated and discussed in this dissertation. By using the numerical optimization procedure, the optimum parametric combinations in bearings can be found with considerations of hydrodynamic lubrication and strength constraints. It is expected that this procedure can become the base in developing STC product design. In order to raise the compression ratio for the scroll pair (i.e. to raise the intrinsic volume ratio) to match even wider loading conditions, a new geometric model of the scroll profiles constructed from an involute of circle with variable radii has been built. One kind of these profiles with greater wrap thickness at the center and decreasing thickness from the inside outwards can provide better strength and rigidity. Finally, this study also demonstrates that the arc and line modifications, used in the conventional scroll profile, can be also applied to this new scroll profile. The two most important purposes, avoiding interference at the center of the scroll pair and boosting the intrinsic volume ratio to match the specified operating conditions, are both achieved by properly choosing one of these two modifications according to design requirements.
|Appears in Collections:||Thesis|
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