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缩机的效率很大程度上取决于不可避免的两相喘振和壁面区域的间隙流，迄今为止，这一点既没有得到很好的理解，也无法计算。其中一个原因是缺乏准确的实验数据和计算模型，无法确定经常在这种机器中处理的非常不对称的制冷剂和油的混合物所需的热物理性质。采取这种情况下，先进的实验方法和部分也分子动力学模拟技术的粘度，界面张力和导热系数的测定等系统应进一步开发和应用在这里作为DFG研究单位为5595的贡献。这将在与上述压缩机应用领域以及所需属性模型和过程模拟方法的开发相关的状态范围内完成。首先从系统选择的模型系统获得的数据，然后从现实的制冷剂-油混合物获得的数据，将推导出结构-性能关系，这将特别有助于模型开发。重点是面向未来的制冷剂，如二氧化碳和丙烷，它们与分子大小不断增加的石油替代品相结合，以接近技术混合物的不对称性。汽液平衡中界面张力和粘度的测量主要采用表面光散射法。对于压缩液相中感兴趣的混合物的粘度测量，将使用振丝法，同时还期望进一步发展应用于颗粒分散体的动态光散射（DLS）。这包括鉴定在分散稳定性方面适合于这种系统的掺杂剂颗粒。上述技术将与拉曼光谱学相结合，将研究准确确定流体成分的校准方法。非平衡分子动力学模拟将被用来访问相关系统的粘度，这是很难检测实验的剪切速率依赖性。虽然确定有关混合物的导热率是第二个供资期的重点，但在此已经使用防护平行板仪器测量了油组分的导热率。相应的混合物的行为的第一个结论是从数据的热扩散率，这是访问DLS应用到液体散装平行的测量SLS。

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.