Showing papers by "Bao Yang published in 2010"

Effect of nanoparticle clustering on the effective thermal conductivity of concentrated silica colloids

Abstract: Recent research on nanofluids has offered particle clustering as a possible mechanism for the abnormal enhancement of the effective thermal conductivity $(k)$ when nanoparticles are dispersed in liquids. This paper was devoted to verify experimentally and theoretically the significance of the effect by altering the cluster structure, size distribution, and thermal conductivity of solid particles in water. Starting with well dispersed ${\text{SiO}}_{2}$ sols in water as a reference system, we control the aggregation kinetics by adjusting $p\text{H}$. Contrary to previous model predictions, the present experiment showed that clustering did not show any discernable enhancement in the thermal conductivity even at high volume loading. A series of fractal model calculations not only suggested that the conductive benefit due to clustering might be completely compensated by the reduced convective contribution due to particle growth, but also recommended the need for higher thermal conductivity and optimized fractal dimension of particles for maximizing the clustering effect.

Thermal- and Phase-Change Characteristics of Self-Assembled Ethanol/Polyalphaolefin Nanoemulsion Fluids

Abstract: The strategy of adding solid particles to fluids for improving thermal conductivity has been pursued for more than one century. Here, a novel concept of using liquid nanodroplets for enhancing thermal performance has been developed and demonstrated in polyalphaolefin nanoemulsion fluids with dispersed ethanol nanodroplets. The ethanol/polyalphaolefin nanoemulsion fluids are spontaneously generated by self-assembly and are thermodynami- cally stable. Their thermophysical properties, including thermal conductivity and viscosity, and impact on convective heat transfer are investigated experimentally. The thermal conductivity enhancement in these fluids is found to be moderate but increases rapidly with increasing temperature in the measured temperature range of 35-75°C. A very remarkable increase in the convective heat transfer coefficient, by a factor of up to 2.2, occurs in the nanoemulsion fluids due to the explosive vaporization ofthe ethanol nanodroplets at the superheat limit (i.e., spinodal states, about 122°C higher than the atmospheric boiling point for ethanol). Such an explosive liquid-vapor phase transition might augment the fluid heat transfer through the heat of vaporization (which intuitively raises the base fluid specific heat capacity) and the fluid mixing induced by the sound waves. The development of such phase-changeable nanoemulsion fluids would open a new direction for thermal fluids studies.

Stress-induced nanostructures through laser-assisted scanning probe nanolithography

Abstract: We demonstrate a methodology using a laser-assisted scanning probe nanolithography (LASPN) technique to generate organized nanostructures. Experimental approach combined with finite element analysis was utilized to study the interfacial interactions between a gold-coated probe of an atomic force microscope and a single crystal silicon substrate. Research results proved that the tip temperature had been raised via LASPN to 900 K at a laser power of 12 mW. Nanolines were formed during sliding while the silicon substrate was heated at a laser power of 5 mW. We propose an energy model to explain the phenomenon. SCANNING 32: 327–335, 2010. © 2010 Wiley Periodicals, Inc.