161
Owing to the larger specific heat capacity of the base salt than that of the nanomaterial used in most cases, the calculated specific heat capacity from Eq. (3) should
be smaller than that of the base salt. Nevertheless, the conventional model has failed
to predict the specific heat capacity after comparing the calculated values to the
experimental results, which implies the more complex mechanism involving the
interactions between the eutectic salt and nanomaterial rather than the simple consideration of weighted principle to be responsible for the variation.
6 Mechanism of the Enhancement of Specific Heat Capacity
Nanomaterials are known to be able to enhance the effective thermal conductivity
of heat transfer fluids (HTFs). By analogy, effective specific heat capacity was
preliminarily thought to be improved in the same way. However, previous results
from both the experimental and theoretical studies are indicative of a distinct
mechanism associated with the interactions between nanomaterials and molten
salts. Apart from some intuitional factors such as temperature, particle concentration
and size, microscopic structures formed within the molten salts with nanomaterials,
and the surface elemental distribution have been investigated for explanation of the
variation of specific heat capacity.
6.1 Factors of Nanomaterials Affecting on the Specific
Heat Capacity
• Size of nanomaterials
Discrepancies in the particle size-dependent specific heat capacity of molten salts
have been found in literatures, which may result from the variation of materials and/
or methods used in different experiments. For example, 1 wt.% SiO 2 nanoparticles
of four different sizes (5, 10, 30 and 60 nm) were added into the binary eutectic
mixtures of NaNO 3 –KNO 3 (40–60 wt.%) [11] and Li 2 CO 3 –K 2 CO 3 (62:38 by molar
ratio) [22], respectively. The results showed that the 60 nm nanoparticles of SiO 2
had a more prominent enhancement in specific heat capacity of the eutectic mixture
of Li 2 CO 3 –K 2 CO 3 than those of other sizes, whilst an equivalent enhancement in
specific heat capacity of the eutectic mixture of NaNO 3 –KNO 3 was obtained regardless of the particle size. In addition, divergent results have been obtained under different experimental conditions. For example, Lu and Huang [38] found that the
specific heat capacity of a solid salt increased as Al 2 O 3 nanoparticle size reduced
from 90 nm to 13 nm whereas the reverse trend occurred to the same salt in liquid state.
Although there are not yet consistent explanations of the effects of the nanomaterial size at present, the incongruent findings have provided good references for
future work in which more comparable experimentation can be conducted.
Nanomaterials Enhanced Heat Storage in Molten Salts
Owing to the larger specific heat capacity of the base salt than that of the nanomaterial used in most cases, the calculated specific heat capacity from Eq. (3) should
be smaller than that of the base salt. Nevertheless, the conventional model has failed
to predict the specific heat capacity after comparing the calculated values to the
experimental results, which implies the more complex mechanism involving the
interactions between the eutectic salt and nanomaterial rather than the simple consideration of weighted principle to be responsible for the variation.
6 Mechanism of the Enhancement of Specific Heat Capacity
Nanomaterials are known to be able to enhance the effective thermal conductivity
of heat transfer fluids (HTFs). By analogy, effective specific heat capacity was
preliminarily thought to be improved in the same way. However, previous results
from both the experimental and theoretical studies are indicative of a distinct
mechanism associated with the interactions between nanomaterials and molten
salts. Apart from some intuitional factors such as temperature, particle concentration
and size, microscopic structures formed within the molten salts with nanomaterials,
and the surface elemental distribution have been investigated for explanation of the
variation of specific heat capacity.
6.1 Factors of Nanomaterials Affecting on the Specific
Heat Capacity
• Size of nanomaterials
Discrepancies in the particle size-dependent specific heat capacity of molten salts
have been found in literatures, which may result from the variation of materials and/
or methods used in different experiments. For example, 1 wt.% SiO 2 nanoparticles
of four different sizes (5, 10, 30 and 60 nm) were added into the binary eutectic
mixtures of NaNO 3 –KNO 3 (40–60 wt.%) [11] and Li 2 CO 3 –K 2 CO 3 (62:38 by molar
ratio) [22], respectively. The results showed that the 60 nm nanoparticles of SiO 2
had a more prominent enhancement in specific heat capacity of the eutectic mixture
of Li 2 CO 3 –K 2 CO 3 than those of other sizes, whilst an equivalent enhancement in
specific heat capacity of the eutectic mixture of NaNO 3 –KNO 3 was obtained regardless of the particle size. In addition, divergent results have been obtained under different experimental conditions. For example, Lu and Huang [38] found that the
specific heat capacity of a solid salt increased as Al 2 O 3 nanoparticle size reduced
from 90 nm to 13 nm whereas the reverse trend occurred to the same salt in liquid state.
Although there are not yet consistent explanations of the effects of the nanomaterial size at present, the incongruent findings have provided good references for
future work in which more comparable experimentation can be conducted.
Nanomaterials Enhanced Heat Storage in Molten Salts