Model-based optimal design of phase change ionic liquids for efficient thermal energy storage

Abstract

The selection of phase change material (PCM) plays an important role in developing high-efficient thermal energy storage (TES) processes. Ionic liquids (ILs) or organic salts are thermally stable, non-volatile, and non-flammable. Importantly, researchers have proved that some ILs possess higher latent heat of fusion than conventional PCMs. Despite these attractive characteristics, yet surprisingly, little research has been performed to the systematic selection or structural design of ILs for TES. Besides, most of the existing work is only focused on the latent heat when selecting PCMs. However, one should note that other properties such as heat capacity and thermal conductivity could affect the TES performance as well. In this work, we propose a computer-aided molecular design (CAMD) based method to systematically design IL PCMs for a practical TES process. The effects of different IL properties are simultaneously captured in the IL property models and TES process models. Optimal ILs holding a best compromise of all the properties are identified through the solution of a formulated CAMD problem where the TES performance of the process is maximized. [MPyEtOH][TfO] is found to be the best material and excitingly, the identified top nine ILs all show a higher TES performance than the traditional PCM paraffin wax at 10 h thermal charging time.