可變壓縮比渦卷式壓縮機之研究

Abstract

對高效能與可變負載之冷凍空調系統而言，為因應其變動負載之需求，搭配變頻馬達之可變壓縮比渦卷式壓縮機已成為目前發展之主流。本研究第一步先探討渦卷之旁通機構，此為裝於固定渦卷背端之閥機構，用於防止當負載變動時因為渦卷幾何線形之固定容積比限制而在壓縮腔內產生之過壓縮；且其亦有避免冷媒剛進入壓縮腔時因過熱度不足而造成的液阻卻。將此步驟發展之旁通機構數學模型整合於一渦卷式壓縮機模擬軟體中，並針對高壓與低壓外殻之壓縮機架構分別進行模擬分析。結果發現不論在何種負載下，設置之旁通孔皆能有效地排除過壓縮與液阻卻。而配合開發中的渦卷式壓縮機也藉由實驗結果驗證此機構在不同負載條件下，能有效地提升壓縮機之效率。 另一方面，針對變動負載之設計需求，也整合最佳化流程於上述渦卷壓縮機模擬軟體中，以輔助產品開發時之參數最佳化設計。並對降低摩擦功之軸承尺寸最佳化問題加以研究，藉最佳化之流程而獲得在考量強度與液動壓潤滑限制條件下，軸承尺寸的最佳參數組合，以作為產品開發時之設計依據。 此外，針對提高渦卷對之壓縮比(亦即提高線形之容積比)以匹配更寬廣的負載需求方面，本研究也發展可變基圓半徑圓漸開線之渦卷線形的數學模型，並以此發展一種中心較厚且由內向外厚度漸薄之圓漸開線渦卷渦片，其強度與剛性於高溫與高壓負載條件下極具優勢。同時也驗證了圓弧與直線此兩種用於傳統渦卷對以修整中心干涉並達到完美嚙合的數學模型，也可應用於此可變基圓半徑圓漸開線之渦卷線形上，進而達成嚙合修正，同時亦可提高渦卷對之壓縮比。

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.