Abstract
The Ragone relation is a facile approach to assess and compare electro-chemical battery performance in terms of two critical performance parameters: power density and energy density. This power and energy nexus is equally relevant for thermal energy storage materials for thermal management applications that require a balance between energy storage capacity and on-demand cooling or heating rates. Here, thermal energy storage is evaluated for sensible heating and for phase-change materials (PCMs). We propose an analytic expression using a lumped mass model for thermal storage through an analogy with heat diffusion that allows for intuitive mapping of materials and components in power-energy space. In addition, a previously proposed figure-of-merit, $\eta_q$, describing the intrinsic capability of PCMs to rapidly absorb or discharge heat is placed in the context of the thermal Ragone (power-energy) relation. This figure of merit serves as a proxy for the cooling power of PCMs and single-phase materials to store thermal energy. Thus, $\eta_q$ plotted against energy density can serve graphically to illustrate performance tradeoffs between different thermal storage materials, as well as composites composed of different materials.
Highlights
A half century ago, Ragone published an overview of electro-chemical and fuel-cell batteries (Ragone, 1968) to compare power and energy performance of batteries in electrical automotive applications, prior to the emergence of plug-in electric vehicle (EVs) (Rotering and Ilic, 2011)
The Ragone relationships for thermal storage materials designed for thermal management were explored, based on an electrothermal analogy
We demonstrated that a lumped thermal mass model worked well to determine the time constant along with the quick positioning of heat power-energy space, which is Ragone relation from the property information
Summary
Reviewed by: Gongnan Xie, Northwestern Polytechnical University, China Xiaofeng Guo, ESIEE Paris, France Patrick Oosthuizen, Queen’s University, Canada. The Ragone relation is a facile approach to assess and compare electro-chemical battery performance in terms of two critical performance parameters: power density and energy density This power and energy nexus is relevant for thermal energy storage materials for thermal management applications that require a balance between energy storage capacity and on-demand cooling or heating rates. A previously proposed figure-of-merit, ηq, describing the intrinsic capability of PCMs to rapidly absorb or discharge heat is placed in the context of the thermal Ragone (power-energy) relation. This figure of merit serves as a proxy for the cooling power of PCMs and single-phase materials to store thermal energy.
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