Phase behavior of oil-refrigerant mixtures – Experimental investigation

喷油旋转式容积式压缩机广泛用于HVAC（加热、通风和空调）系统中制冷剂的压缩。压缩机的效率在很大程度上取决于压缩机机械部件中的两相喘振和间隙流。由于两相流动的复杂性和工质热力学性质模型的缺乏，两相流动的计算目前仍具有挑战性。为了推进这类计算，必须改进热力学性质模型，这需要准确的实验性质数据。然而，进一步的发展目前受到严重缺乏压缩机中流体的实验热力学数据的限制，压缩机中的流体是油和制冷剂的高度不对称混合物。在此背景下，研究单位FOR 5595的这一子项目的主要目标是对油-制冷剂混合物的热力学性质进行全面准确的测量，重点是密度和汽液相行为。这些数据将最终作为开发油-制冷剂混合物的准确热力学性质模型的基础。当然，高度不对称混合物的混合行为对最初为不对称性较小的混合物开发的实验装置提出了挑战。因此，设想改进和进一步发展现有的实验装置，用于研究增加不对称性的二元混合物，最终目标是研究油-制冷剂混合物。在研究股内共同选定了要测量的二元系统，并以越来越不对称的方式列出如下：（1）丙烷+正戊烷和CO2 +正癸烷;（2）丙烷+正癸烷和CO2 +正十六烷;（3）如果可能的话，丙烷+角鲨烷和CO2 +角鲨烷。拉曼光谱将用于测量气体（制冷剂）在液体（油替代物）中的溶解度。对于纯油和油-制冷剂混合物在液相中的密度测量，将使用振动管密度测定法。为了研究混合物的汽液相行为，将采用微波凹腔谐振器，从而开发一种新的微波腔设计，以研究完整的汽液相行为，包括温度，压力，相分数以及共存相的组成和密度。此外，实验工作的固有部分是将测量系统处的混合物制备和样品处理的基础设施向非对称混合物推进，以确保在已知组成下进行测量。

Oil-injected rotary type positive displacement compressors are broadly used for the compression of refrigerants in HVAC (Heating, Ventilation and Air Conditioning) systems. The compressor efficiency is largely determined by the two-phase surge and gap flows in the compressors’ mechanical components. Due to the complexity of the two-phase flow and the lack of accurate thermodynamic property models of the working fluids, the calculation of these flows is nowadays still challenging. To advance such calculations, thermodynamic property models must be improved, which requires accurate experimental property data. However, further development is currently limited by the significant lack of experimental thermodynamic data for the fluids in the compressors, which are highly asymmetric mixtures of oil and refrigerant. Against this background, the key objective of this subproject of the Research Unit FOR 5595 is to carry out comprehensive and accurate measurements of thermodynamic properties of oil-refrigerant mixtures, focusing on density and vapor-liquid phase behavior. These data will ultimately serve as basis for developing accurate thermodynamic property models of the oil-refrigerant mixtures. Certainly, the mixing behavior of the highly asymmetric mixtures poses challenges to the experimental setups originally developed for less asymmetric mixtures. Therefore, it is envisioned to improve and further develop existing experimental setups for the investigation of binary mixtures of increasing asymmetry with the final goal to study oil-refrigerant mixtures. Binary systems to be measured have been jointly selected within the Research Unit and are listed with increasing asymmetry as follows: (1) propane + n-pentane and CO2 + n-decane (2) propane + n-decane and CO2 + n-hexadecane and (3) if possible propane + squalane and CO2 + squalane. Raman spectroscopy will be used to measure gas (refrigerants) solubility in liquids (oil surrogates). For density measurements of pure oils and oil-refrigerant mixtures in the liquid phase, vibrating-tube densimetry will be utilized. To study the vapor-liquid phase behavior of the mixtures, microwave re-entrant cavity resonators will be employed, whereby a new microwave cavity design is to be developed to investigate the full vapor-liquid phase behavior including temperature, pressure, phase fraction as well as compositions and density of the coexisting phases. Moreover, inherent part of the experimental work is to advance the infrastructure for mixture preparation and sample handling at the measuring systems towards asymmetric mixtures to ensure that measurements will be conducted at known compositions.