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

注油回转式正排量压缩机的效率在很大程度上取决于壁面不可避免的两相喘振和间隙流，而这两相喘振和间隙流到目前为止还没有得到很好的理解和计算。造成这种情况的一个原因是缺乏准确的实验数据和计算模型，以满足通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特性。考虑到这种情况，需要进一步发展和应用先进的实验方法和部分分子动力学模拟技术来测定这类体系的粘度、界面张力和导热性，作为对DFG研究单位for 5595的贡献。这将在与所提到的压缩机的应用领域和所需属性模型和过程仿真方法的开发相关的状态范围内完成。从首先为系统选择的模型系统和后来为实际的制冷剂-油混合物获得的数据中，将推导出结构-性质关系，这将特别有助于模型的发展。重点是面向未来的制冷剂，如二氧化碳和丙烷，它们与越来越大的分子尺寸的石油替代品相结合，以接近技术混合物的不对称性。气液平衡中界面张力和黏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，将使用振动线法，同时进一步发展应用于颗粒分散的动态光散射（DLS）。这包括根据这种系统的分散稳定性来确定合适的掺杂颗粒。上述技术将与拉曼光谱相结合，研究精确测定流体成分的校准方法。非平衡分子动力学模拟将用于获取相关系统粘度的剪切速率依赖关系，这在实验中很难检测到。虽然确定感兴趣的混合物的导热系数是第二个目标资助期的重点，但在这里已经使用保护平行板仪器测量了油组分的导热系数。首先从热扩散率的数据中得出相应的混合行为的结论，这些数据是由DLS与SLS并行应用于液体体的测量得到的。

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.