Cao Bing-Yang

Experimental Studies on Thermal and Electrical Properties of Platinum Nanofilms

We experimentally studied the in-plane thermal and electrical properties of a suspended platinum nanofilm in thickness of 15 nm. The measured results show that the in-plane thermal conductivity, the electrical conductivity and the resistance-temperature coefficient of the studied nanofilm are much less than those of the bulk material, while the Lorenz number is greater than the bulk value. Comparing with the results reported previously for the platinum nanofilm in thickness of 28 nm, we further find that the in-plane thermal conductivity, the electrical conductivity and the resistance-temperature coefficient decrease with the decreasing thickness of the nanofilm, while the Lorenz number increases with the decreasing thickness of the nanofilm. These results indicate that strong size effects exist on the in-plane thermal and electrical properties of platinum nanofilms.

Rarefied Gas Flow in Rough Microchannels by Molecular Dynamics Simulation

The molecular dynamics simulation method is applied to investigate the rarefied gas flow in a submicron channel with surface roughness which is modelled by an array of triangle modules. The boundary conditions are found to be determined not only by the Knudsen number but also the roughness, which implies that the breakdown of the Maxwell slip model under the conditions that the surface roughness is comparable to the molecular mean free path. The effects of the rarefaction and the surface roughness on the boundary conditions and the flow characteristics are strongly coupled. The flow friction increases with increasing roughness and with decreasing Knudsen number.

Thermal Conductivity of Carbon Nanotubes Embedded in Solids

A carbon-nanotube-atom fixed and activated scheme of non-equilibrium molecular dynamics simulations is put forward to extract the thermal conductivity of carbon nanotubes (CNTs) embedded in solid argon. Though a 6.5% volume fraction of CNTs increases the composite thermal conductivity to about twice as much as that of the pure basal material, the thermal conductivity of CNTs embedded in solids is found to be decreased by 1/8-1/5 with reference to that of pure ones. The decrease of the intrinsic thermal conductivity of the solid-embedded CNTs and the thermal interface resistance are demonstrated to be responsible for the results.

Thermal Conduction in a Single Polyethylene Chain Using Molecular Dynamics Simulations

Research on the thermal conduction in a single polymer chain is significant for the improvement of the thermal property of bulk polymer materials. We calculate the thermal conductivity of a single polyethylene (PE) chain by using both the Green—Kubo approach and a nonequilibrium molecular dynamics simulation method. The results suggest that the thermal conductivity of an individual polymer chain is very high although bulk PE is a thermal insulator, even divergent in our case. Moreover, the thermal conductivity of PE chains is observed to increase with the chain length.

Experimental study on the in-plane thermal conductivity of Au nanofilms

Abstract The in-plane thermal conductivity of Au nanofilms with thickness of 23 nm, which are fabricated by the electron beam-physical vapor deposition method and a suspension technology, is experimentally measured at 80–300 K by a one-dimensional steady-state electrical heating method. Strong size effects are found on the measured nanofilm thermal conductivity is much less than that of the bulk material. With the increasing temperature, the nanofilm thermal conductivity increases. This is opposite to the temperature dependence of the bulk property. The Lorenz number of Au nanofilms is about three times larger than the bulk value and decrease with the increasing temperature, which indicates the invalidity of the Wiedmann-Franz law for metallic nanaofilms. *Supported by National Natural Science Foundation of China (Grant No. 50606018)

Thermal conductivity of dielectric nanowires with different cross-section shapes

Non-equilibrium molecular dynamics simulations have been performed to investigate the effect of the cross-section shape on the thermal conductivity of argon nanowires. Some typical cross-section shapes, such as triangle, square, pentagon, hexagon and circle, are carefully explored. The simulation results show that with the same cross-sectional area of the regular polygons, the thermal conductivities decrease with the reduction of the sides of the polygons, and the thermal conductivity of the circular nanowire is larger than those of the other polygonal ones. Phonon gas kinetic theory is used to analyse the phonon transport in nanowires, and the concept of equivalent diameter is proposed to illustrate the characteristic dimension of the none-circular cross-section.

Advances of capillary filling of Newtonianfluids in micro- and nanochannels

Capillary filling is extensively involved in natural science and engineering technology, such as oil recovery, building conservation, ink printing, etc. Due to large surface to volume ratio, capillary action is very prominent at micro- and nonoscale regime, and recent years it has triggered a tremendous acceleration of research related to the capillary filling process in micro- and nanochannels. For instance, the capillary action is used to eliminate some additional accessories such as electric drive devices or syringe pumps, which can greatly simplify the design of microfluidic and nanofluidic devices. All these facts show that a thorough understanding of the kinetics of capillary-driven filling in micro- and nanochannels is of great significance. Almost a century ago, Lucas and Washburn reported an analytical solution for capillary filling of Newtonian fluids in a small cylindrical capillary tube: the filling distance is proportional to the square root of time, which is also known as the classical LW equation. Although the LW equation can well describe macroscopic capillary filling process, it’s availability at micro- and nanoscale regime is still an open question, which has attracted a lot of attention. This paper summarizes the progress of capillary filling kinetics in micro- and nanochannels in views of theoretical models, numerical simulations and experimental studies. All the three perspectives indicate that the capillary filling process should be discussed by dividing into four stages as follows: (1) purely inertial time stage, where the filling distance is proportional to the time t ; (2) visco-inertial time stage, where the inertia force, capillary force and viscous force have comparable effect on the filling kinetics; (3) purely viscous time stage, where the capillary force is balanced by viscous force and the filling distance is linearly related to the t 1/2; (4) the gravity should be considered when the pipe is vertical and there is a viscous and gravitational time stage. In purely viscous time stage, the LW equation can qualitatively describe the capillary filling process in micro- and nanochannels. Quantitatively, however, significant deviations between the experiment or simulation results and theoretical expectations have been observed in capillary filling process. Although several factors are considered to explain the deviation, such as the dynamic contact angle, bubble formation, electro-viscous effect and other factors, there is no unified understanding on the capillary filling kinetics. Finally, possible pending problems are summarized based on the results in previous work. In addition, brief introduction and prospect have been made on capillary filling of non-Newtonian fluids.