Hari Sriram Multiscale Mechanics and Nanotechnology Laboratory Advisor: Sumit Sinha Ray, Dr. Suman Sinha Ray, Dr. A.L. Yarin August 2, 2012.

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

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

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

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

.

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

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

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

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

Flow characteristics with water

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

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.

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

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.

Future Work: Heat Transfer Experimental Setup

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

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

Questions?

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.

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.

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