Refrigerant, lubricant, solubility, dillution measurement, capacitor sensor
The solubility of refrigerants in the lubricant is a key factor for the life time of a compressor. The new Low Global Warming Potential (LGWP) refrigerants are showing generally higher solubility in lubricants than usual refrigerants. It is important to compare the dilution changes in the oil sump during compressor operation due to refrigerants properties. Sampling is a measurement method commonly used to measure dilution in working compressor but can be time consuming and it disturbs the system behavior. Additional security precautions need to be taken when sampling flammable refrigerant. This paper presents a measurement method based on the permittivity properties of fluids and their mixtures. The investigations consider the use of HFC, HC, HFO and their blends. In most of the cases presented, the method used delivers satisfying results. But care should be taken for some fluids that exhibit polar properties. This paper also presents measurement results of viscosity and dilution in the oil sump of a compressor. Results showed a very good correlation with sampling and PTVS curves (Daniel plots) from suppliers when running at stabilized conditions, using a linear mixing rule for relative permittivity. This method allows measurement without disturbing the system and decreases the time needed for the experiment.