Experimental investigation of viscosity, interfacial tension, and thermal conductivity of oil-refrigerant mixtures by light scattering and conventional techniques

喷油旋转式容积式压气机的效率很大程度上依赖于壁面区域不可避免的两相喘振和间隙流动，到目前为止，这种流动还没有得到很好的理解和计算。其中一个原因是缺乏准确的实验数据和计算模型来计算通常在这类机器中加工的非常不对称的制冷剂和油的混合物所需的热物理性质。考虑到这种情况，将进一步开发和应用先进的实验方法，部分还包括分子动力学模拟技术，以确定此类体系的粘度、界面张力和导热系数，作为对DFG研究单位5595的贡献。这将在与上述压缩机的应用领域以及所需特性模型和工艺模拟方法的开发相关的状态范围内进行。首先从系统选择的模型系统获得的数据，然后从实际的制冷剂-油混合物获得的数据，将得出结构-性质关系，这将特别有助于模型的开发。重点是面向未来的制冷剂，如二氧化碳和丙烷，它们与分子尺寸越来越大的石油替代品结合在一起，以接近技术混合物的不对称性。在汽液平衡中，界面张力和粘度的测量主要是通过表面光散射(SLS)来实现的。对于压缩液体中感兴趣的混合物的粘度测量，将使用振弦法，同时还希望进一步发展应用于颗粒分散体的动态光散射(DLS)。这包括识别适合于此类系统的分散稳定性的掺杂剂颗粒。上述技术将与拉曼光谱技术相结合，为此将研究准确确定流体组成的校准方法。非平衡分子动力学模拟将被用来获得相关体系粘度的剪切速率依赖关系，这在实验上是很难检测到的。虽然确定感兴趣的混合物的热导率是第二个目标资金期的重点，但在这里已经使用有保护的平行板仪器测量了石油组分的这一性质。首先，从热扩散系数的数据中得出相应的混合物行为的结论，热扩散系数是通过与SLS测量平行地应用于液体主体的DLS来获取的。

The efficiency of oil-injected rotary positive displacement compressors depends strongly on the inevitable two-phase surge and gap flow in the wall region, which to date is neither well understood nor calculable. One reason for this is the lack of accurate experimental data and calculation models for the required thermophysical properties of the very asymmetric mixtures of refrigerants and oils often processed in such machines. Taking up this situation, advanced experimental methods and partly also molecular dynamics simulation techniques for the determination of viscosity, interfacial tension, and thermal conductivity of such systems shall be further developed and applied here as a contribution to the DFG Research Unit FOR 5595. This will be done in state ranges that are relevant both for the field of application of the compressors mentioned and for the development of the required property models and of process simulation methods. From the data obtained first for systematically selected model systems and later for realistic refrigerant-oil mixtures, structure-property relationships will be derived, which will contribute in particular to model development. The focus is on future-oriented refrigerants such as CO2 and propane, which are combined with oil surrogates of increasing molecular size to approach the asymmetry of technical mixtures. The measurement of interfacial tension and viscosity in vapor-liquid equilibrium is mainly performed by surface light scattering (SLS). For viscosity measurements of the mixtures of interest in the compressed liquid phase, the vibrating-wire method will be used, while a further development of dynamic light scattering (DLS) applied to particle dispersions is additionally aspired. This includes the identification of dopant particles suitable in terms of dispersion stability for such systems. The aforementioned techniques will be combined with Raman spectroscopy, for which calibration approaches to accurately determine fluid composition will be investigated. Non-equilibrium molecular dynamics simulations will be used to access the shear-rate dependence of the viscosity of the relevant systems, which is hardly detectable experimentally. While the determination of the thermal conductivity of the mixtures of interest is a focus of a targeted second funding period, this property is already measured here for the oil components using a guarded parallel-plate instrument. First conclusions on the corresponding mixture behavior are drawn from data for the thermal diffusivity, which is accessed by DLS applied to the liquid bulk in parallel to the measurements by SLS.