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Hari Sriram
Multiscale Mechanics and Nanotechnology Laboratory
Advisor: Sumit Sinha Ray, Dr. Suman Sinha Ray, Dr. A.L. Yarin
August 2, 2012
Carbon Nanotubes (CNTs) are group of carbon
molecules rolled up into cylindrical structure and are
used in different parts of science such as
microelectronics, biomedical applications etc.
We are using CNTs as carriers of phase change
materials (PCM), like wax, which will serve as a
coolant in microelectronic devices
Transmission Electronic
Microscopy (TEM) image
of PCM intercalated CNTs
Sinha-Ray, S., R. P. Sahu, and A. L. Yarin. "Nano-encapsulated Smart Tunable Phase Change Materials." Soft Matter 7.19 (2011): 8823-827
Find a surfactant that will create a stable suspension as
well as to optimize the CNT and surfactant
concentration
Find the highest weight percentage of CNTs in
suspension that can flow through microchannels
Find the flow characteristics of CNT suspensions with
and without wax
Using the flow characteristics of the wax intercalated
CNTs to see how the suspension absorbs heat in a
microelectronic system by making a prototype of it
with a constant heat flux condition
Pressure from the air line
two way valve
pushes the plunger down
The plunger pushes the oil
down through the pipe
which in turn pushes the
CNT suspension through
the microchannel
The valve is used to release
the oil into the syringe
.
Q exp erimental
Air Line
Air
Plunger
Oil Chamber
Pressure Gauge
Valve Assembly
Suspension Chamber
V
t
three way valve
Microchannel
The connected line is the theoretical flow rate and the scattered points are the
experimental flow rate
We have found sodium dodecylbenzenesulfonate (NaDDBS) to
be the surfactant that creates the most stable suspension
The ratio of CNT concentration to NaDDBS concentration was
found to be 1:10
(a)
(b)
CNT Suspension after
16hrs of sonication and
left to settle for 1 hour
with:
(a) 1mL of NaDDBS
(b) No added surfactant
M. F. Islam, E. Rojas, D. M. Bergey, A. T. Johnson and A. G. Yodh: Nano Letters., 2003, 3, 269-273
We have varied CNT weight percentage for CNT
suspensions as well as wax intercalated CNTs
Experimental flow rate was observed to be 1.2-1.4 times
greater than theory
The experimental flow rate was greater for higher
concentrations of CNTs
Flow Rate of different concentrations of CNT suspension: (a) 0.1% (b) 0.3% (c)
0.6% (d) 1%. The connected line is the theoretical flow rate and the scattered
points are the experimental flow rate
Flow Rate of different concentrations of wax intercalated CNT suspensions: (a)
0.15% (b) 0.2% (c) 0.5% (d) 0.7%. The connected line is the theoretical flow rate
and the scattered points are the experimental flow rate
Formation of nanobubbles caused by the surfactant
Desolubilization of gas in the suspension causes
the formation of the nanobubbles
λ is referred to as the slip length, which is defined
as the fictitious distance below the surface where
the no-slip boundary condition would be satisfied.
.
Q exp erim ental
.
Q theoretical
1
4
No Slip
Partial Slip
Perfect Slip
a
λ=0
λ
0<λ<∞
λ=∞
C. Tropea, A. L. Yarin, and J. F. Foss: ‘Springer Handbook of Experimental Fluid Mechanics’, 1219-1240; 2007, Berlin, Springer.
As the concentration of CNT increased, the concentration of surfactant
increased and therefore created more slip along the walls of the channel
As constant heat flux is added to system, the fluid
absorbs the heat and through convection the heat is
dissipated in the wax
We assume that the flow is at steady state and that all
the heat that is put in the system should be taken out
The heat transfer coefficient will tell us how much of
the heat is taken out of the system
𝒒
𝒉=
𝑨(𝑻𝒆 − 𝑻𝒊
q is the heat put into the system
A is the surface area of the channel
Te-Ti is the change in overall
temperature
J. P. Holman: ‘Heat Transfer’, 253-257; 2010, New York, McGraw-Hill.
Flow characteristics for suspensions of CNT as high
as 1%/wt without wax and 0.7%/wt for wax
intercalated CNT has been seen
The surfactant NaDDBS produces slip along the
walls of the microchannel, producing a higher flow
rate
Vary concentrations of wax intercalated CNTs and
measure the heat transfer coefficient
The financial support from the National Science
Foundation, EEC-NSF Grant # 1062943 is gratefully
acknowledged
Special Thanks to Dr. Christos Takoudis, Dr. Gregory
Jursich
The Poiseuille equations gives the flow profile of a fluid through a
cylindrical pipe with a circular cross sections
Assumptions that are made are that the flow is laminar, fully
developed and at steady state
The fluid is assumed to be viscous and incompressible
The Poiseuille equation is derived from the Navier-Stokes equations
which are the basis the describe the velocity profile of fluids
dz
vz
1 dP
4 dz
R (1
2
r
2
R
2
)
r is the radius of the
fluid
dP/dz is the change
in pressure
R
r
dr
Flow through a cylindrical
channel with circular cross
section
Munson, Bruce Roy, T. H. Okiishi, and Wade W. Huebsch. Fundamentals of Fluid Mechanics. Hoboken, NJ: J. Wiley &
Sons, 2009.
Velocity at the walls are zero
due to friction and the
maximum velocity is at the
center (No-slip boundary
condition)
Q theoretica
R P
4
.
l
8L
Q is the volumetric flow rate
R is that radius of the channel
P is the pressure at the exit valve
μ is the viscosity of the carbon
nanotubes
L is the length of the microchannel
Munson, Bruce Roy, T. H. Okiishi, and Wade W. Huebsch. Fundamentals of Fluid Mechanics. Hoboken, NJ: J. Wiley &
Sons, 2009.