Reduction of supercooling of water by TiO₂ nanoparticles as observed using differential scanning calorimeter

Abstract

Aqueous dispersions of Titania nanoparticles were cooled using differential scanning calorimetry (DSC). The nanoparticles reduce the supercooling of water by acceleration of nucleation. The experimental results demonstrated the important role in water crystallisation by the internal surface of the sample holder, and that stable nanofluids are required for the measurements to investigate the effect of nanoparticles on freezing. But for dispersions at low concentrations, such as 0.05 wt% and 0.1 wt%, the starting temperatures of freezing were found to be unusual at the cooling rates of 3 C/min and 4.5 C/min, namely they were even lower than that of the deionised (DI) water. It is found that surface controlled nucleation (SCN) is dominant at low cooling rates, while volumetric controlled nucleation (VCN) is dominant at high cooling rates.

Effects of nanoparticles and sample containers on crystallization supercooling degree of nanofluids

“…Wu et al (2009) investigated the cold storage performance of an Al 2 O 3 -H 2 O nanofluid and found that adding 0.2% Al 2 O 3 nanoparticles can shorten the crystallization time of the nanofluid by 20.5% and reduce its SD by 70.9% [8]. Mo et al (2013) and reported that TiO 2 nanoparticles can reduce the SD of water [9,15]. Kumaresan et al (2013) and discovered that scattered multiwalled carbon nanotubes in deionized water can serve as a nucleating agent to reduce the SD of water significantly [10,11].…”

“…Recent studies have suggested the use of nanofluids as phase-change energy storage media [4][5][6][7][8][9][10][11][12][13][14]. As a common phasechange cold storage medium, water is environmentally friendly and cheap; however, water still has such limitations as high crystallization supercooling degree (SD) and relatively poor heat conductivity.…”

Non-isothermal crystallization of aqueous nanofluids with high aspect-ratio carbon nano-additives for cold thermal energy storage

“…Therefore, the presence of nanoparticles may also be able to perform as nuclei in addition to their primary functionality of enhancing the thermal conductivity of nanofluids. In the literature, the freezing point (supercooling degree), latent heat of crystallization, and crystallization kinetics of aqueous nanofluids have been characterized, both isothermally and non-isothermally, for a variety of metallic, metal oxide, and high aspect-ratio carbon nano-additives [27][28][29][30][31][32][33][34][35][36][37][38].…”

Inorganic Salt Hydrate for Thermal Energy Storage

“…Nanoparticles like TiO 2 and Al 2 O 3 [88][89][90][91] are often added into PCMs to increase melting rate and reduce problems of refrigerating mediums such as environmental pollution, low thermal conductivity, large size and high installing and running cost. Hui et al [92] found that LiCl/H 2 O and NH 3 /H 2 O pairs have good performance among several absorbent/refrigerant pairs, which can be used for air conditioning application and subzero applications, respectively.…”