A novel experimental rig to investigate the effect of the refrigerant on the oil supply of a variable capacity reciprocating compressor

The oil pumping plays a key role in the reliability and efficiency of compressors adopted in refrigeration systems. However, the investigations available in the literature on this subject do not consider the presence of the refrigerant and its effects on the oil supply. This paper reports the development of a novel experimental rig to measure the flow rate provided by the oil pump of a hermetic variable capacity reciprocating compressor considering the presence of the refrigerant in contact with the lubricating oil. A visualization system was also developed to investigate the transient outgassing phenomenon that takes place in the oil supply system when a sudden depressurization occurs, such as during the compressor startup. Measurements were carried out with the AB ISO VG 5 oil and the R-600a as the refrigerant fluid under different pairs of evaporating and condensing temperatures and compressor speed. Considering that the AB ISO VG 5 oil and air are immiscible, tests were also performed with air to isolate the effect of the refrigerant fluid on the oil supply. The results show that the oil flow rate is decreased due to the presence of refrigerant, with this effect becoming slightly stronger as the evaporating temperature is increased. The visualization system revealed that the outgassing brought about by the solubility between oil and refrigerant fluid has the potential to temporarily interrupt the oil supply.