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Fig. 14 Intensity I versus
wave vector q measured in
ethanol-in-PAO
nanoemulsion fluids [
11
]
5
Ethanol in PAO nanoemulsions
Alcohol/PAO Nanoemulsions
4
3
2
1
0.01
0.1
Wave Vector q(A
-1
)
5.1.2 Thermal Conductivity of Ethanol-in-PAO Nanoemulsion Fluids
Figure
15
shows the relative thermal conductivity in Ethanol-in-PAO nano-
emulsion fluids as a function of the ethanol loadings. The observed conductivity
increase in the Ethanol-in-PAO nanoemulsion fluids is rather moderate. The
prediction by the Maxwell model is also plotted in Fig.
15
for comparison. The
relative thermal conductivity is defined as k
eff
/k
o
,wherek
o
and k
eff
are thermal
conductivities of the base fluid and nanoemulsion fluids, respectively. The
effective medium theory reduces to Maxwell's equation for suspensions of well-
dispersed, noninteracting spherical particles,
k
eff
k
o
¼
k
p
þ
2k
o
þ
2/
ð
k
p
ffi
k
o
Þ
k
p
þ
2k
o
ffi
/
ð
k
p
ffi
k
o
Þ
ð
7
Þ
where k
o
if the thermal conductivity of the base fluid, k
p
is the thermal conductivity
of the particles, and / is the particle volumetric fraction. This equation predicts
that the thermal conductivity enhancement increases approximately linearly with
the particle volumetric fraction for dilute nanofluids or nanoemulsion fluids (e.g.,
/ \ 10 %), if k
p
[ k
o
and no change in particle shape. It can be seen in this figure
that the relative thermal conductivity of Ethanol-in-PAO nanoemulsion fluids
appears to be linear with the loading of ethanol nanodroplets over the loading
range from 0 to 9 vol%. However, the magnitude of the conductivity increase is
rather moderate in the ethanol-in-PAO nanoemulsion fluids, e.g., 2.3 % increase
for 9 vol% (k
PAO
= 0.143 W/mK and k
alcohol
= 0.171 W/mK [
35
,
83
]). No strong
effects of Brownian motion on thermal transport are found experimentally in those
fluids although the nanodroplets are extremely small, around 0.8 nm.
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