Linking dynamics and equilibrium thermodynamics: entropy scaling and density scaling of siloxane mixtures and other working fluids for Carnot batteries

如果要实现高效率，SPP中雄心勃勃的自上而下的方法需要关于热力学平衡和传输性质的准确数据。在逆向设计中，理论上描述这些性质的合理方程是确定最佳工质和操作条件所必需的。输运性质的预测方程的发展远远落后于平衡性质的发展，因此这是拟议项目的目标。事实上，平衡性质数据和预测方程的更好可用性使得探索输运和平衡热力学之间的联系变得引人注目。本文将以同构理论为背景，用熵标度和密度标度来模拟纯流体和混合物的剪切粘度和导热系数。该项目的目标之一是制定一种值得信赖的方法和建议，以便将熵标度应用于运输属性建模。将对罗森菲尔德在基于硅氧烷及其混合物研究基础上的熵标度理论的开创性工作的可用修改进行批判性评估。罗森菲尔德认为，输运性质，当用适当的物理维度标度时，是残余熵的单变量函数。本项目还侧重于密度标度的理论和方法的发展，因为与熵标度相反，密度标度不需要亥姆霍兹能量状态方程。申请者的准备工作表明，使用与流体有效硬度相关的恒定有效密度标度指数，可以将密度标度的唯一变量转换为残余熵的单变量函数。在这个意义上，提出了密度标度及其与熵标度的关系的研究。这将需要使用基于Mie势的模型流体和混合物，这允许排斥相互作用的变化。作为一类真实的流体，我们将研究直链和环状的硅氧烷化学族及其混合物。化学族的选择将提供研究模型参数和分子结构之间的联系的可能性，这是反向设计所必需的。在混合的情况下，重点将放在混合规则和高度不对称的混合上，其中单变量行为预计会被分解。通常，分子模拟技术将被用来获得均匀分布的杂化输运性质数据集以及剩余熵数据。该项目被认为是战略计划的一部分，包括与其他合作伙伴的高度合作。它不仅限于运输性质比例计划的制定，还包括平衡性质的供应以及根据其他战略石油项目合作伙伴的具体需要研究其他流体。

The top-down methodology ambitioned in the SPP requires accurate data on thermodynamic equilibrium and transport properties if high efficiencies are to be achieved. In inverse design, theoretically sound equations describing these properties are necessary to identify optimal working fluids and operating conditions. The development of predictive equations for transport properties has remained well behind that of equilibrium properties, such that it is the objective of the proposed project. In fact, the better availability of equilibrium property data and predictive equations makes exploring the link between transport and equilibrium thermodynamics compelling. Entropy scaling and density scaling, having isomorph theory as a background, will be addressed for modeling the shear viscosity and thermal conductivity of pure fluids and mixtures. One of the goals of this project is the elaboration of a trustworthy methodology and recommendations for the application of entropy scaling to transport property modeling. A critical evaluation of the available modifications of Rosenfeld’s pioneering work on entropy scaling theory based on studies of the siloxanes and their mixtures will be performed. Rosenfeld suggested that transport properties, when scaled with the appropriate physical dimensions, are an univariate function of the residual entropy. This project also lays a focus on the theoretical and methodological development of density scaling, since it, contrary to entropy scaling, does not require the availability of a Helmholtz energy equation of state. Preparatory work of the applicant showed that the use of a constant effective density scaling exponent, related to the fluid’s effective hardness, can transform the unique variable of density scaling into a univariate function of residual entropy. In this sense, a study of density scaling and its relationship with entropy scaling is proposed. This will require the use of model fluids and mixtures, based on the Mie potential, which allows for variation of the repulsive interaction. As a class of real fluids, the siloxane chemical family, linear and cyclic, as well as mixtures thereof will be studied. The choice of a chemical family will offer the possibility to investigate the link between model parameters and molecular structure, which is required for inverse design. In case of mixtures, emphasis will be put to mixing rules and to highly asymmetric mixtures, where the univariate behavior is expected to break down. Generally, molecular simulation techniques will be employed to obtain evenly distributed hybrid transport property data sets as well as residual entropy data. This project, conceived as a part of the SPP, includes a high level of collaboration with other partners. It is not limited to the development of transport property scaling schemes, but also includes the supply of equilibrium properties and the study of other fluids according to the specific needs of other SPP project partners.