Experimental investigation of the rheological and phase change behavior of adipic acid as a phase change material (PCM) for thermal energy storage at 150 °C

Phase change materials (PCM) can store and release thermal energy mostly through a transition from solid to liquid and vice versa. This transition and its related parameters such as melting point, enthalpy and heat capacity were most often studied from a thermodynamic point aspect. Investigating the phase transition from a rheological point of view can provide us with important information such as viscosity change during the transition and in the melt. Considering the importance of natural convection during the melting of a PCM, the rheological knowledge can improve the estimations resulting from the numerical analysis of a phase change transition. However, there are a few studies on rheological behavior of PCMs. Here, the rheological behavior of an organic PCM, adipic acid, is studied. This PCM melts at 150 degrees C which corresponds to a medium temperature range for application in industrial waste heat recovery. Rotational and oscillatory tests under thermal insulation have been performed using a controlled stress rheometer and a plate geometry. Finally, the heat flow measured by Differential Scanning Calorimetry (DSC) is compared to the rheological oscillatory test results to provide a detailed information of phase transition range. To the authors best knowledge, this study is the first study in the rheology of a PCM at medium to high temperature (150 degrees C).