Ionic liquids as heat transfer fluids – An assessment using industrial exchanger geometries

Abstract The objective of this work is to carry out a practical assessment of using a typical ionic liquid as a heat transfer fluid. In order to carry out such an assessment, the thermophysical properties, namely, density, heat capacity, viscosity, and thermal conductivity need to be known for the chosen ionic liquid. A typical ionic liquid chosen for the current study is 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, ([bmim][Tf2N]) based on the availability of thermophysical properties over a range of temperatures. The assessment was carried out by simulating the heat transfer characteristics for this ionic liquid in two different types of heat exchangers, namely, a plate heat exchanger and a shell and tube heat exchanger. The results of the heat transfer behavior for the ionic liquid in these two exchanger types are described. These results are also compared with the results for a conventional industry standard heat transfer fluid. It is demonstrated that although the heat transfer characteristics, in terms of heat transfer coefficient, for the chosen ionic liquid are not particularly attractive, it is possible to obtain reasonable heat transfer coefficients by judicious selection of heat exchanger type, heat exchanger configuration and possible use of heat transfer enhancement technology. Finally conclusions are drawn about the potential of ionic liquids as heat transfer fluids taking into account the heat transfer assessment as well as a number of other practical considerations. From a practical perspective the paper reflects a typical work flow used by a practicing thermal engineer when heat transfer performance characteristics for a given fluid or a given heat exchanger type are to be assessed, with a view of optimizing the overall equipment or system performance.