Passive Thermal Energy Storage Systems Research Articles

Thermo-optically responsive phase change materials for passive temperature regulation

Many phase change materials (PCMs) experience a change in transparency when undergoing a phase transition. These thermo-optically responsive materials can be used to generate passive temperature control systems for building enclosures. The integration of optical and thermal switches into smart temperature-controlling elements requires rationally designed PCMs featuring tunable optical and thermal properties. Two polymers, poly (Octadecyl methacrylate) (PSMA) and poly(2-(2-(octadecyloxy) ethoxy) ethyl methacrylate) (PE2SMA) were synthesized and evaluated for their potential use in passive thermal energy storage systems. UV–Visible Spectroscopy, Near Infra-Red Spectroscopy, and Differential Scanning Calorimetry were used to evaluate the effect that changes in the polymer chemical structure had on the optical and thermal properties of the resulting materials. Insertion of a 6-atom flexible spacer (diethylene glycol) between the pendant crystalline motif and the polymer backbone of PSMA resulted in increases of latent heat storage capacity from 62 J/g to 94 J/g and thermal conductivity from 0.218 W/mK to 0.318 W/mK. Notably, insertion of a flexible spacer also resulted in a melting transition temperature increase from 37.7 °C for PSMA to 48 °C for PE2SMA. The visible transmittance of the polymers increased from 0% to 90% upon transition from crystalline to amorphous state. This study presents a synthetic strategy to control thermal and optical properties of polymeric PCMs materials. The material properties and structure-property relationships derived from this study will enable the refinement of the models used to predict the performance of passive temperature-regulating systems. More accurate models will guide the development of the thermo-responsive polymeric materials required for better perfoming temperature-regulating building enclosures.

Polyvinyl Alcohol-salt Hydrate Mixtures as Passive Thermal Energy Storage Systems

Inorganic salt hydrates are promising candidates as latent heat storage materials entailing, for example, a high thermal energy storage density and cheap price [1,2] in spite that they have many handicaps. For almost all applications, Phase change materials (PCMs) have to be encapsulated, that is, they have to be hermetically sealed within barrier containments, preferably within small microcapsules. Encapsulation improves heat transfer, cycling stability, and material compatibility with the environment. However, no attempt has been completely successful to microencapsulate salt hydrates so far due to the high surface polarities of these substances, edge alignment effects, their tendency to alter their water content [3]. This work is aimed to encapsulate some commonly used salt hydrates; sodium sulphate decahydrate (Na2SO4.10H2O) and calcium chloride hexahydrate (CaCl2.6H2O) in a hydrophilic polymer; polyvinyl alcohol (PVA) stably for passive thermal energy storage systems. So that an economically beneficial application mean will be validated.