Dew-Point Densities of Fluid Mixtures - New Approaches for Measurement and Modeling

提出的研究项目的目的是开发新的实验技术来准确测量流体混合物的露点密度，以克服现有技术中的困难。这包括对吸附效应的量化，从而大大减少了不确定性。将形成一种新的理论，它将首次将热力学性质测量和吸附现象这两个公认的领域结合在一起。此外，测量数据将被用来建立多参数基本状态方程，从而将检验关于拟合策略的新想法。流体混合物的相行为的研究是热物理性质研究的主要焦点。为了将这一研究成果应用于科学和工业，例如在天然气处理和碳捕获和储存领域，需要准确描述液体和蒸汽之间的相界的性质模型。发展这类模型的最重要的前提是准确的实验数据，然而，现有的数据集存在着差距和不足。为了建立能够描述混合物相平衡的状态方程，主要使用VLE(汽液平衡)数据。然而，考虑饱和液体和饱和蒸汽密度的汽液平衡数据很少。但正是这些数据提供了关于汽液平衡状态的完整实验信息，这是发展现有状态方程所绝对需要的。20世纪80年代，NIST测量了流体混合物的精确饱和液体密度，在鲁尔大学，到目前为止，专门设计了一种新的高精度实验设备来测量这种类型的数据。相比之下，流体混合物露点密度的准确数据几乎是不存在的。测量包括饱和液体和饱和蒸汽密度在内的流体混合物的全套汽液平衡性质的实验方法非常缺乏。所谓的分析测量方法的最重要的不确定度来源是对组成分析的相进行采样，因为发生了重大问题(例如，改变组成和扰乱平衡)。此外，对于气态，密度测量技术不够准确。因此，需要一种合成方法，即准确地知道样品的组成，并结合精确的密度测量技术。在这种情况下，最近的研究表明，当不考虑吸附效应和毛细管凝聚时，准确地知道组成是不够的。这些令人不安的影响扭曲了测量的密度，因此，需要理解和考虑它们。

The aim of the proposed research project is to develop new experimental techniques for the accurate measurement of dew-point densities of fluid mixtures, which overcome difficulties in currently existing techniques. This includes the quantification of sorption effects, thus, significantly reducing uncertainties. A new theory will be forged, which will combine, for the first time, the well-established fields of thermodynamic property measurement and sorption phenomena. Furthermore, the measured data will be used to establish multiparameter fundamental equations of state, whereby new ideas regarding the fitting strategy will be examined.The investigation of the phase behavior of fluid mixtures is a major focus of thermophysical property research. To make the outcome of this research applicable for science and industry, for example in the fields of natural gas processing and carbon capture and storage, property models accurately describing the phase boundary between liquid and vapor are required. The most important prerequisite for the development of such models are accurate experimental data, however, there are gaps and deficiencies in the presently existing data sets. For the development of equations of state, which are able to describe the phase equilibrium of mixtures, mainly VLE (vapor-liquid equilibrium) data are used. Nevertheless, only very few VLE data consider the saturated liquid and saturated vapor densities. But it is exactly these kinds of data that provide complete experimental information on the VLE state, which would be absolutely required to advance the state of the art of the existing equations of state.Accurate saturated liquid densities of fluid mixtures were measured at NIST in the 1980s, and at Ruhr-University a new and highly accurate experimental apparatus is available by now specifically designed to measure this type of data. In contrast, accurate data for fluid mixture dew-point densities virtually never exist.Experimental approaches to measure the full set of VLE properties of fluid mixtures including the saturated liquid and saturated vapor densities are very scarce. The most significant source of uncertainty of so-called analytic measurement approaches is sampling the phases for composition analysis because substantial problems occur (e.g., changing the composition and disturbing the equilibrium). Additionally, the density measurement techniques are not sufficiently accurate for gaseous states. Hence, a synthetic approach, which means the composition of the sample is accurately known, in combination with an accurate density measurement technique is required. In this context, recent studies have shown that exactly knowing the composition is not sufficient when sorption effects and capillary condensation are not considered. These disturbing effects distort the measured density and, therefore, they need to be understood and taken into account.