Reed valve, Oil, Droplet generation, Flow visualization
Oil in circulation in refrigeration systems generally degrades their thermodynamic and reliability performance. The vast majority of compressors used in the residential, automotive and light commercial air conditioning and refrigeration use pressure actuated reeds as the discharge valves. These valves are the gateway for the oil to leave the compressor to the rest of the system. In this work, a residential AC scroll compressor was equipped with sight windows on the discharge plenum and visualization studies were carried out using high speed imaging and processing techniques to identify the moment of oil mist generation, and also provide quantification of the droplet size and velocity distributions inside the discharge plenums. The compressor was run in a full system setup with measuring devices for mass flow rate, pressure, temperature and OCR (by sampling according to ASHRAE Standard 41.4). Oil viscosity was varied from 9cSt to 68cSt along with OCR(0.5%-3%) and compressor volumetric flow rate, all while using R134a as the refrigerant. It was found that a very fine mist (drops with diameters below 88 micrometers) is generated right at the start of the opening process of the valve followed by interaction between the vapor flow and liquid (oil-refrigerant mixture) flow with the internal geometric features of the discharge plenum to generate larger droplets. It was observed that at higher volumetric flow rates, smaller droplets are produced and that the more viscous the oil, the larger the droplets generated. During the work it became clear the need to investigate the characteristics of the film breakup since there were strong visual indications that the majority of oil droplets came from that process. Those characteristics are addressed on part II of this work.