Journal
APPLIED ENERGY
Volume 138, Issue -, Pages 193-201Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.apenergy.2014.10.077
Keywords
Non-isothermal crystallization; Thermal energy storage; Phase change materials; Aqueous nanofluids; Carbon nanotubes; Graphene
Categories
Funding
- National Natural Science Foundation of China (NSFC) [51276159, 51206142]
- China Postdoctoral Science Foundation (CPSF) [2012M511362, 2013T60589]
- Open Fund Program of the Key Laboratory of Efficient Utilization of Low and Medium Grade Energy (Tianjin University), Ministry of Education of China [201301-102, 201301-302]
- Scientific Research Foundation (SRF) for the Returned Overseas Chinese Scholars, Ministry of Education of China
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Non-isothermal crystallization of aqueous nanofluids in the presence of two types of high aspect-ratio carbon nano-additives, i.e., carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), was characterized by means of differential scanning calorimetry (DSC). A parametric investigation was performed on various concentrations of the nanofluids as well as various cooling rates during the DSC tests. In addition to the supercooling degree and latent heat of crystallization, the crystallization kinetics was also analyzed by both the Ozawa method and a modified Ozawa-based method. It was shown that dilute loading of CNTs or GNPs leads to reduction of the supercooling degree up to 5 degrees C due to the nucleating effect. The planarly-shaped GNPs featuring large contact area perform better than CNTs in facilitating heterogeneous nucleation, which greatly suppress crystal growth during the late phase of non-isothermal crystallization. In contrast to the case of GNPs, CNTs may be able to accelerate crystallization up to nearly 37% at relatively dilute loadings, especially when the cooling rate is low. The CNT-based aqueous nanofluids exhibit more balanced performance in supercooling degree, latent heat of crystallization, and crystallization kinetics, which may be utilized as an emerging candidate of phase change materials for cold thermal energy storage. (C) 2014 Elsevier Ltd. All rights reserved.
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