Critical analysis of the T-history method: A fundamental approach

Abstract

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

The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) and under Grant agreement N°PIRSES-GA-2013-610692 (INNOSTORAGE), and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The work is partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). Dr. Luisa F. Cabeza would like to thank the Catalan Government for the quality accreditation given to the research group GREA (2014 SGR 123).