hari sriram multiscale mechanics and nanotechnology laboratory advisor: sumit sinha ray, dr. suman...
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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
Flow of Carbon Nanotubes under pressure driven conditions
through microchannels
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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
Background and Motivation
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
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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
Project Goals
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Experimental Setup
three way valve
two way valve
AirAir Line
Plunger
Oil Chamber
Valve Assembly
Pressure Gauge
Suspension Chamber
Microchannel
Pressure from the air line 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
t
VQ erimental
exp
.
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The connected line is the theoretical flow rate and the scattered points are the experimental flow rate
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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
Stable CN T suspensions
CNT Suspension after 16hrs of sonication and left to settle for 1 hour with:(a)1mL of NaDDBS(b)No added
surfactant
(a) (b)
M. F. Islam, E. Rojas, D. M. Bergey, A. T. Johnson and A. G. Yodh: Nano Letters., 2003, 3, 269-273
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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
Results
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Results
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
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Flow characteristics with water
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Results
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
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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.
Reasons for higher flow rate
No Slip Partial Slip Perfect Slip
λ=0 0<λ<∞λ λ=∞
.
exp
.
41erimental
theoretical
Q
aQ
C. Tropea, A. L. Yarin, and J. F. Foss: ‘Springer Handbook of Experimental Fluid Mechanics’, 1219-1240; 2007, Berlin, Springer.
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Average Slip Length vs. Concentration
As the concentration of CNT increased, the concentration of surfactant increased and therefore created more slip along the walls of the channel
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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
Future Work: Heat Transfer in Laminar Flow Tube
q is the heat put into the systemA is the surface area of the channelTe-Ti is the change in overall temperature
𝒉=𝒒¿¿
J. P. Holman: ‘Heat Transfer’, 253-257; 2010, New York, McGraw-Hill.
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Future Work: Heat Transfer Experimental Setup
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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
Summary
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The financial support from the National Science Foundation, EEC-NSF Grant # 1062943 is gratefully acknowledged
Special Thanks to Dr. Christos Takoudis, Dr. Gregory Jursich
Acknowledgments
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Questions?
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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
Additional Slides: Poiseuille flow through circular channels
R
rdr
dz
Flow through a cylindrical channel with circular cross section
)1(4
12
22
R
rR
dz
dPvz
r is the radius of the fluiddP/dz is the change in pressure
Munson, Bruce Roy, T. H. Okiishi, and Wade W. Huebsch. Fundamentals of Fluid Mechanics. Hoboken, NJ: J. Wiley & Sons, 2009.
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Additional Slides: Poiseuille equation
Q is the volumetric flow rateR is that radius of the channelP is the pressure at the exit valveμ is the viscosity of the carbon nanotubesL is the length of the microchannel
Velocity at the walls are zero due to friction and the maximum velocity is at the center (No-slip boundary condition)
Munson, Bruce Roy, T. H. Okiishi, and Wade W. Huebsch. Fundamentals of Fluid Mechanics. Hoboken, NJ: J. Wiley & Sons, 2009.
L
PRQ ltheoretica
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