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 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.