Coalescing oil separator for compressors

Abstract

Oil separation is commonly needed in air conditioning or refrigeration systems to reduce the oil circulation rate and keep the oil inside the compressor. For compactness, the oil separation structure integrated into the compressor is more and more popular than traditional external oil separator. However, a quantitative guideline for the design of oil separation structure is missing for irregular geometry and realistic flow condition at the compressor discharge. This paper presents coalescence, one of the basic mechanisms of droplet separation, studied by flow visualization and analytical models. The misty oil flow through separator is visualized by a high-speed camera and analyzed quantitatively. Oil droplet size distribution is estimated by video processing. Important flow details are revealed, including oil droplet collision, oil droplet coalescence, oil film breakup, and re-entrainment. Separation efficiency is estimated by the ratio between drained and incoming oil mass flow rate. Pressure drop is also measured to evaluate the cost brought by separation structures. An analytical model for coalescing oil separator is developed based on the mass flow balance through multiple layers of coalescing separators. Development of the model starts with the experimental and analytical analysis of first one wire, then a serious of wires to come to a wire pad. The results of the model are verified by experimental measurements in a full vapor compression system with R134a and PAG oil. The results of the model show good agreement with experiment and conclusion provides guidelines for oil separator design and operation.