Leakage in scroll compressors is a dynamic process affected by several factors including: machining tolerances, thermal effects, operating instabilities, wrap deflections, oil circulation, oil distribution, refrigerant/oil solubility, etc. Previous investigations attempting to characterize the leakage processes inside the scroll compressor pump assembly have yielded little information into the nature of the mechanisms involved. Most analytical models treat leakage in the scroll compressor as a Fanno flow process and do not include the effects of oil; while most experimental efforts involve measuring steady-state leakage flow rates through fixed clearances. Limited knowledge is available regarding the effects of oil on the leakage characteristics of scroll compressors. For these reasons, tests were conducted to determine the effects of oil circulation on the performance of an operating low-side scroll compressor. Due to the adverse effects of high system oil circulation, efforts were also made to develop and test an oil separator and return system internal to the compressor. Various amounts of oil were injected into the compression pockets of a three ton scroll compressor in an attempt to: 1) characterize the oil film behavior on the scroll tips, flanks, and thrust surface, 2) monitor the leakage processes across the scroll tips and flanks using high-speed pressure transducers, and 3) determine how the oil is distributed in the scrolls. The compressor performance, noise, and compression process characteristics were recorded during testing at both steady-state and transient operating conditions. The test results indicate that at low-pressure ratio conditions, leakage losses are governed by thermal effects. At mid-pressure ratio conditions, leakage losses are minimum and are related to the machining tolerances and local deformations, while at high-pressure ratio conditions, leakage is increased because of minute separations of the scrolls as a result of significant back-flow during the discharge process. Overall, indications are that an optimum level of oil circulation exists that results in a significant increase in operating efficiency and decrease in radiated noise (both shown to be a strong function of operating pressure ratio).
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