Critical analysis of the T-history method : a fundamental approach09 Mar 2017
Energy storage is a key challenge to a sustainable energy supply. To design new storage systems accurate and representative thermal property measurements are essential. The T-history method is quick and uncomplicated, however numerous adaptations have been proposed over the years. In this study these methods have been classified and critically assessed based on their mathematical formulation and experimental configuration. They can be broadly categorized according to one of three assumptions regarding the heat transfer coefficient for natural convection: it is constant either as a function of time or temperature, or it is negligible. This work proves in addition that the heat transfer coefficient for natural convection, varies both as a function of time and temperature. This is demonstrated both experimentally and through rigorous simulation of the proposed configurations. Thus T-history methods which show the most promise for precise and unambiguous measurements eliminate convection by making conduction the dominant thermal resistance in the system. These techniques can be tailored to different materials and do not require a simultaneous reference due to the use of a rigorous fundamental model compared to the lumped parameter approximation. The addition of heat flux sensors to quantify actual heat losses are recommended for absolute measurement certainty.