Conference Year
2018
Keywords
spool, loss analysis, indicated losses, novel compressor, valve loss
Abstract
An analysis of the indicated and frictional losses is presented for a light-commercial prototype spool compressor. The spool compressor prototype was instrumented with four high-speed pressure sensors, three in the compression process and one in the discharge valve plenum. These sensors were triggered with a high-fidelity rotary encoder attached to the compressor motor shaft. This coupling of rotational position and pressure measurements allowed the development of an indicator (pressure v. volume) diagram for the compression process. Additionally, the added sensor in the discharge valve plenum allowed for a de-coupling of discharge valve losses and flow losses within the discharge plenum itself. The analysis shows that the suction and compression losses for this prototype compressor are relatively small compared with the discharge/valve losses. The total losses during the discharge process are generated by pressure drop and backflow through the discharge valve ports as well as when gas flows from the discharge plenum to out of the compressor body. The compressor was tested at three shaft speeds (900, 1300, 1620 rpm) at a condensing and evaporating temperatures ranging from 100 – 120 °F (37.8 – 48.9 °C) and 25 -60 °F (-3.8 – 15.6 °C), respectively at a fixed suction superheat of 30 °R (16.7 K). It was found that the total losses during the discharge process were the dominant indicated losses in the compressor and the discharge plenum losses accounted for between 32 and 66% of the total losses during the discharge process. As a result of this study, a small modification to the discharge plenum of the compressor was incorporated which resulted in a 1-3% increase in overall isentropic efficiency without additional modifications to the compressor mechanism or valves.