The free vibration and instability of fluid-conveying multi-wall carbon nanotubes (MWCNTs) are studied based on an Euler-Bernoulli beam model. A theory based on the transfer matrix method (TMM) is presented. The validity of the theory was confirmed for MWCNTs with different boundary conditions. The effects of the fluid flow velocity were studied on MWCNTs with simply-supported and clamped boundary conditions. Furthermore, the effects of the CNTs’ thickness, radius and length were investigated on resonance frequencies. The CNT was found to posses certain frequency behaviors at different geometries. The effect of the damping corriolis term was studied in the equation of motion. Finally, a useful simplification is introduced in the equation of motion.

Stable and homogeneous silicone oil based nanofluids of multi-walled carbon nanotubes (MWNTs) were prepared by using hexamethyldisiloxane as surfactant. The used MWNTs were cut by mechanical ball-milling approach following strong acid treatment. Scanning electronic microscopy results show that the MWNTs disperse well in the silicone oil. The addition of hexamethyldisiloxane reduces the viscosity of silicone oil greatly in all the studied temperatures. It is different from some water based nanofluids with surfactant. The minor viscosity augmentation of silicone oil based MWNT nanofluid with high thermal conductivity make it the ideal media in high burden of heat transfer and heat transfer enhancement in special condition. As expected, the viscosity of the nanofluid increases with MWNT volume fraction, but decreases with temperature. The 0.54 vol% MWNT dispersions with the addition of 0.6 wt % hexamethyldisiloxane show no MWNT precipitation for a couple of weeks.

Thermal management in electronics become more challenging as the size of electronics decreases, yet, the heat generated from electronics still increases. To enhance cooling efficiency of conventional cooling schemes such as heat pipes, we experimentally present a use of electrowetting on dielectric (EWOD) digital microfluidic technique to force the cooling liquid medium to move to hot spot area. In this paper, firstly, two different EWOD devices were compared in their cooling performance. One is a system using one plane device and sessile droplet of cooling medium and the other is a system using two parallel planes and liquid is sandwiched in between. Secondly, two types of liquids were used and compared as the cooling medium. De-ionized (DI) water and room temperature ionic liquid (RTIL) have been investigated. RTILs are thermally stable thanks to their low vapor pressure. In addition to thermal stability, RTIL can be tailored task specifically by altering cations and anions. Different experiments were conducted to study the capacity of IL’s to change the surface temperature of the hotspot generated and this was compared with that of DI water. The latter showed higher capacity to remove heat, while evaporation problem was predominant in the sandwiched setup. Three different ionic liquids, 1-butyl-3-methylimidazolium chloride or [BMIM]Cl, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide or [BMIM]Ntf2, and [CMIM]FeCl 4 showed less effect on changing the surface temperature compared to water. It is due to generally lower heat conductivity and higher viscosity of ILs than water. However, RTILs showed high thermal stability by resulting in no evaporation during cooling process while water had vigorous evaporation. Nanofluid of RTIL and multiwall carbon nanotubes (MWCNT) mixture has been tested as the first step toward enhancing thermal conductivity of RTIL.

We report a method to prepare surfactant-free water based nanofluids containing multi-walled carbon nanotubes (CNTs). The as prepared CNTs with hard dispersibility, after being cut by mechanical ball-milling approach following strong acid treatment, can be directly dispersed into water. The thermal conductivity of the nanofluids is optimized by controlling the CNT length and straightness. It is realized by changed the ball-milling times. The thermal conductivity enhancement of water based CNT nanofluids with volume fraction of 1% attains 29.5% by controlling the CNT length and straightness when the temperature is 63.9°C.

The flow of a fluid that is in a state of saturated vapor at the upstream side of a channel is considered. The flow is described by applying the balances of mass, momentum and energy. One-dimensional flow and heat conduction is assumed. Account is taken of the Joule-Thomson effect and, for contact angles smaller than 90°, of the capillary pressure given by the Young-Laplace equation and of the vapor pressure reduction at a curved meniscus due to Kelvin’s equation. For a diameter of the channel below a certain threshold the vapor condenses fully, liquid flows through a part of the channel, the fluid evaporates at a location within the channel and vapor flows through the remaining part of the channel. The threshold diameter below of which the fluid condenses fully is a function of the fluid properties and of the effective thermal conductivity of the fluid-filled channel. The threshold diameter lies in the range from a few tens of nanometers for bad heat conductors to a few hundreds of nanometers for very good heat conductors such as multi-walled carbon nanotubes. Solutions are given for the flow problem with a contact angle of 90° and with contact angles smaller than 90°. The mass flux is considerably larger for contact angles smaller than 90°. However, as long as the contact angle is smaller than approx. 70°, the mass flux is nearly independent of the contact angle.

The interface thermal resistance (ITR) of the interface between vertically aligned multiwalled carbon nanotube (MWCNT) arrays and the SiO 2 /Si and Inconel substrates was investigated. Experimental results were compared with theoretical predictions for the ITR across nanoconstrictions. The model considers classical constriction effects and contributions due to diffuse mismatch thermal resistance. Experimental values of the ITR are much larger than the model predictions. The observed discrepancy may be due to the imperfect mechanical contact between the tubes and substrate or additional contributions to ITR due to the presence of a catalyst layer at the interface.

Multiwall carbon nanotubes show potential for use in various micro- and nanofluidic devices, since they resemble cylindrical channels used in the macroscopic world. However, in situ experimental studies of fluid behavior in nanotubes or nanochannels have been rare. In this work, transmission electron microscopy experiments are performed on closed-end multiwall carbon nanotubes filled with an aqueous multiphase fluid. The nanotubes form an experimental apparatus that is a few orders of magnitude smaller than the smallest channels used in other fluidic experiments. These nanotubes are synthesized hydrothermally, using Ni as a catalyst, and they contain segregated aqueous liquid and gas inclusions with clearly defined interfaces. Using electron irradiation, the multiphase fluid inside individual nanotubes is excited thermally, by expanding and contracting the electron beam. The excellent wettability of the graphitic inner tube walls by the aqueous fluid and the mobility of this liquid in the nanotubes are observed in real time with nanometer-scale resolution. Interface dynamic phenomena are visualized, as driven by thermocapillary forces as well as by evaporation and condensation. The hydrothermal nanotubes examined herein offer a promising platform for studying the behavior of multicomponent, multiphase fluids in nanosize channels at high-pressure conditions. The phenomena documented in this study demonstrate the potential of implementing such tubes in future nanofluidic devices.