Civil Engineering Reference
In-Depth Information
merits and limitations; however, the size of the nanoparticles can be controlled
more efficiently with the wet-chemical sol-gel approach. The elucidation on the
detailed preparation methodology of the different types of nanomaterials has been
reported in Capek (
2004
).
9.2 Preparation of PCM Embedded with Nanomaterials
The nanomaterials obtained using any of the aforementioned methods have to be
doped into the pure (base) PCM in order to realize the thermophysical property
changes in the PCM. The nanomaterials are initially characterized for their surface
morphology, surface structure, crystallization, thermal stability, etc., using the
respective analytical techniques including scanning electron microscope (SEM),
transmission electron microscope (TEM), Fourier transform infrared (FTIR)
spectroscopy, X-ray diffraction (XRD), thermogravimetric-differential thermal
analysis (TG-DSC) and so on.
As the first step in doping nanomaterials into the pure PCM, the weight pro-
portions of nanoparticles with respect to the pure PCM are to be determined. In
general, the weight proportions of nanomaterials, usually represented in weight
percentage (wt%), are represented by the relation given by
Weight of the nanomaterial
Weight of the nanomaterial
þ
Weight of the PCM
Weight percentage of nanomaterial
¼
ð
Þ
ð
11
Þ
For instance, the weight of nanoparticles (W
np
, g) that is required for the
preparation of 0.1 wt% of 100 g of PCM solution can be calculated using
the above relation, as given by
0
:
1
100
¼
w
np
w
np
þ
99
:
9
ð
12
Þ
Based on the computation, the required quantity of the nanoparticles is
dispersed into the pure PCM using high-frequency ultrasonic vibration technique.
The ultrasonication helps the powder nanoparticles to be evenly distributed into
the pure PCM solution; thereby the nanoparticles can stay stable without getting
settled down in the solution.
In order to keep the nanomaterials stable on a long run, the surfactants or
stabilizing agents are added to the PCM solution, which would maintain the
nanoparticles from being agglomerated and settle down due to the intermolecular
forces of attraction. However, the mixing of surfactant with PCM solution may
sometimes affect the thermal properties of the PCM being subjected to several
thermal cycles.
