Environmental Engineering Reference
In-Depth Information
Table 1
PCMs with potential use in thermal fluids [
21
,
22
]
Compound name
Phase change
temperature (C)
Thermal conductivity
(W/mK)
Latent heat
(J/g)
Solid-
liquid
Water
0
0.6 (liquid)
334
Myristic acid + Capric
24
0.15 (liquid)
147
CaCl
2
6H
2
O
29
0.56 (liquid)
192
Na
2
SO
4
10H
2
O
32
0.54 (liquid)
251
Paraffin C17
22
0.15 (liquid)
215
Paraffin C18
28
0.15 (liquid)
245
Paraffin C19
32
0.15 (liquid)
222
Capric Acid
32
0.15 (liquid)
152
Zn(NO
3
)
2
6H
2
O
36
0.47 (liquid)
147
Indium
157
82 (solid)
29
FC-72
56
0.06 (liquid)
88
Liquid-
vapor
Ethanol
78
0.2 (liquid)
855
Water
100
0.6 (liquid)
2260
Trihydroxy methyl-
aminomethane
134.5
0.22
285
Solid-
solid
Pentaglycerin
81
0.22
193.2
Neopentyl glycol
43
0.22
131.5
unit mass, and DT is the temperature difference between the heat transfer surface and
the bulk fluid. For example, a 5 % mass fraction of solid-liquid phase-changeable
hexadecane (melting point, 291 K) may enhance the effective heat capacity of FC-
72 by up to 100 % at DT = 10 K. Therefore, the use of PCMs as the dispersed
particles will be able to boost the thermal properties of thermal fluids much more
significantly than non-PCM particles at the same volume fraction.
Current PCMs available for thermal fluid application can be divided into three
main categories: solid-solid, solid-liquid, and liquid-vapor transitions. The ther-
mophysical properties of the state-of-the-art PCMs with potential use in thermal
fluids are listed in Table
1
. Liquid-vapor PCMs, such as ethanol and water, have a
much larger latent heat and therefore result in a higher heat transfer rate, but a
condenser is needed for vapor condensation. Solid-liquid PCMs have small vol-
ume change during phase transition, and therefore the suspension of solid-liquid
phase change particles can be used in the thermal management system designed
for single-phase fluids. Solid-solid PCMs do not involve the liquid phase, so there
is no concern about liquid leakage and thermal expansion during phase transition.
3 PCM Microcapsules
PCM microcapsules comprise a PCM core and a polymer or inorganic shell. The
microcapsules can avoid the PCM leakage and the possible interaction between the
PCM and the matrix. This section will discuss synthesis and characterization of
two types of PCM microcapsules; one is paraffin-polymer microcapsules that are
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