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

拟议研究项目的目的是开发新的实验技术，以精确测量流体混合物的露点密度，克服目前现有技术中的困难。这包括吸收效应的量化，从而显著降低不确定度。一个新的理论将被锻造出来，它将第一次把热力学性质测量和吸收现象这两个已确立的领域结合起来。此外，测量数据将用于建立多参数基本状态方程，由此将研究拟合策略的新思路。流体混合物相行为的研究是热物性研究的一个主要热点。为了使这项研究的成果适用于科学和工业，例如在天然气加工和碳捕获与储存领域，需要准确描述液体和蒸汽之间相边界的属性模型。建立此类模型最重要的前提是准确的实验数据，然而目前已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，主要使用汽液平衡数据。然而，只有很少的VLE数据考虑了饱和液体和饱和蒸汽密度。但正是这些类型的数据提供了完整的VLE状态的实验信息，这绝对需要推进现有状态方程的最新技术。在20世纪80年代，NIST测量了流体混合物的精确饱和液体密度，而在鲁尔大学，一种新的、高度精确的实验装置现在已经可用，专门用于测量这种类型的数据。相比之下，流体混合物露点密度的精确数据几乎从未存在过。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VLE特性的实验方法非常缺乏。在所谓的分析测量方法中，最重要的不确定性来源是对组成分析的相进行采样，因为会出现实质性问题（例如，改变组成和扰乱平衡）。此外，密度测量技术对气体状态的测量不够精确。因此，需要一种综合方法，这意味着样品的组成是准确已知的，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冷凝时，确切地知道成分是不够的。这些干扰效应扭曲了测量的密度，因此，它们需要被理解和考虑。

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.