Early on, Wilkes [1] discussed the possibility of using ionic liquids (ILs) as thermal fluids, particularly for high temperature heat transfer applications such as solar thermal energy generation. Stimulated mainly by their low volatility and high thermal stability, several other authors have also raised the possibility of using ILs for this and related purposes.[2-5] Other researchers have investigated the use of ILs as co-fluids with water, carbon dioxide or other substances in absorption cooling applications. Some of the key thermophysical properties necessary for assessing the feasibility of using ILs in these applications have been measured, including thermal conductivity, density, viscosity, melting point/glass transition temperature, the solubility of carbon dioxide and water and heat capacity. In general, experimental densities and viscosities tend to be more available than the other properties, and often there are missing data for particular ILs or the properties are not measured under conditions of interest. Depending on the application, one or more of these properties will be critically important, while others may be less so.Being able to understand and even predict why a given IL has a particular set of properties is important, because the vast number of potential ILs makes it impossible to synthesize and characterize all of them. Ideally, one would like to perform a limited number of experiments on a carefully selected set of ILs and use this information along with modeling and theory to try to understand structure-property relationships. Here we report our efforts at using molecular simulations to predict the key thermophysical properties of ILs necessary for application as thermal fluids. We show that special sampling methods are often required to obtain accurate phase equilibria and that force field development is key for making accurate predictions.  References [1] Van Valkenburg, M. E.; Vaughn, R. L.; Williams, M.; Wilkes, J. S. Thermochemistry of Ionic Liquid Heat-Transfer Fluids. Thermochim. Acta 2005, 425, 181-188.[2] Holbrey, J. D. Heat Capacities of Common Ionic Liquids? Potential Applications as Thermal Fluids? Chim. Oggi-Chem. Today 2007, 25, 24-26.[3] Chen, H.; He, Y.; Zhu, J.; Alias, H.; Ding, Y.; Nancarrow, P.; Hardacre, C.; Rooney, D.; Tan, C. Rheological and Heat Transfer Behaviour of the Ionic Liquid, [C4mim][NTf2]. Int. J. Heat Fluid Flow 2008, 29, 149-155.[4] Paulechka, Y. U. Heat Capacity of Room-Temperature Ionic Liquids: A Critical Review. J. Phys. Chem. Ref. Data 2010, 39, 033108.[5] Liu, H.; Maginn, E.; Visser, A. E.; Bridges, N. J.; Fox, E. B. Thermal and Transport Properties of Six Ionic Liquids: An Experimental and Molecular Dynamics Study. Ind. Eng. Chem. Res. 2012, 51, 7242-7254.

Assessing the performance of ionic liquids as thermal fluids via molecular simulation

248th National Meeting (2014)

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