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Expanded Vermiculite: A Promising Natural Encapsulation Material of LiNO 3 , NaNO 3 , and KNO 3 Phase Change Materials for Medium‐Temperature Thermal Energy Storage
Author(s) -
Deng Yong,
Li Jinhong,
Nian Hongen
Publication year - 2018
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201800135
Subject(s) - materials science , thermal energy storage , thermal conductivity , phase change material , nano , thermal stability , latent heat , chemical engineering , thermal , composite material , thermodynamics , physics , engineering
In the study, with LiNO 3 , NaNO 3 , and KNO 3 as medium‐temperature phase change materials (PCMs) and expanded vermiculite (EVM) as the encapsulation material, form‐stable composite PCMs (fs‐CPCMs) are prepared. The experimental value of maximum encapsulation mass fractions of LiNO 3 ‐EVM, NaNO 3 ‐EVM, and KNO 3 ‐EVM is, respectively, 84.6, 85.7, and 87.0 wt%, which is lower than the theoretical value since the pore structures of EVM are not fully filled by PCMs. SEM results indicate that the PCMs are uniformly distributed and embedded into the pores or on the surfaces of EVM. The excellent chemical compatibility of PCMs with EVM is confirmed by XRD and FT‐IR results. DSC tests indicate the phase change temperatures of three fs‐CPCMs are between 243.1 and 325.1 °C and that latent heats are between 83.1 and 295.4 J g −1 . After 100 melting/solidification cycles, the decrease in latent heats of fs‐CPCMs are below 1.91%, exhibiting desirable thermal reliability. The thermal conductivity of LiNO 3 ‐EVM, NaNO 3 ‐EVM, and KNO 3 ‐EVM is, respectively, 0.51, 0.44, and 0.33 W/(m K), indicating acceptable thermal energy charging/discharging rate. TGA analysis reveal that fs‐CPCMs show good thermal stability within the designed working temperature range. Therefore, EVM is a promising natural encapsulation material for medium‐temperature heat storage.