Reed valve, Oil film, Breakup pattern, Mist generation, 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. This work is focused on the breakup process of the film that is formed between a reed valve and its seat. Emphasis is given on visualization of the breakup pattern and determination of the critical valve lift and velocity at which the film breaks during typical compressor operation. Preliminary experiments were carried out outside of the compressor environment, using a typical valve plate from a reciprocating compressor for household refrigerators. Observations of the breakup pattern show that the liquid film does not remain continuous until breakup into ligaments and droplets. In fact the stretched liquid film is first broken up into equally spaced liquid columns and then by means of the drag force promoted by the vapor flow due to the pressure difference it is blown away from the valve edge and starts the atomization process into a fine mist. Additional experiments were also carried out with two different oil viscosities (32cSt & 120cSt), and four different operating frequencies ranging from 30Hz-60Hz in a scroll type compressor operating under typical residential air conditioning conditions. The valve lift was inferred by visualization and determined using image processing techniques implemented in MATLAB.. The visualizations were also utilized to quantify the droplet cloud velocities, and also valve critical lift before oil is ejected from the gap between valve and seat.