Hyun Uk Kang

Estimation of Thermal Conductivity of Nanofluid Using Experimental Effective Particle Volume

The thermal conductivities of nanofluid containing a small amount of ultra-dispersed diamond (UDD), silver, and silica nanoparticles were measured using a transient hot-wire method. To explain the enhancement of thermal conductivity of nanofluid, the effective volume of nanoparticles was used instead of the real volume to predict the thermal conductivity of nanofluid. The liquid layering on the surface of nanoparticles may be described as the effective volume of nanoparticles. This liquid layering is one important mechanism of the heat transfer in nanofluids. The effective volume of nanoparticles was estimated from high shear viscosity of nanofluid using the Einstein equation. The Hamilton–Crosser model with an effective volume fraction of nanoparticles resulted in better correlation for the thermal conductivities of nanofluids.

Synthesis of Silica Nanofluid and Application to CO2 Absorption

Abstract This study focused on the synthesis of stable nanofluids and their direct application to the CO2 absorption process. A sol-gel process was used as the synthesis method of nanoparticles in nanofluid. The particle size and stability were determined by SEM image and zeta potential of the nanofluid. Three types of nanofluids containing approximately 30 nm, 70 nm, and 120 nm particles were synthesized and all nanofluids had a stable zeta potential of approximately − 45 mV. Addition of nanoparticles increased the average absorption rate of 76% during the first 1 minute and total absorption amount of 24% in water. The capacity coefficient of CO2 absorption in the nanofluid is 4 times higher than water without nanoparticles, because the small bubble sizes in the nanofluid have large mass transfer areas and high solubility.

Synthesis of hydrophilic coating solution for polymer substrate using glycidoxypropyltrimethoxysilane

Hydrophilic coating solutions were synthesized by adding glycidoxypropyltrimethoxysilane (GPS) to the colloidal silica suspensions adjusted to different pH. The coating solutions were coated on polyethyleneterephthalate (PET) film substrates. The pH of the colloidal silica suspensions adjusted before adding the GPS had a profound effect on chemical structure of the coating solutions and hydrophilic property of the coating films. 29Si NMR spectroscopic studies showed that the solution prepared under an acidic condition (pH 4) consisted of hydrolyzed GPS monomers without siloxane bond and dimer with one siloxane bond, whereas that under a basic condition (pH 9.6) was made up larger oligomers with two or three siloxane bonds. Contact angles for water in the coating films prepared under acidic conditions exhibited smaller than those under basic conditions, indicating more hydrophilic in acidic conditions. In especial, in the case of coating films preparedunder highly acidic conditions (pH 1 and 2), the contact angles were less than 5°, which is superhydrophilic.

Characterization and Photoluminescence of CdS Nanoparticles Synthesized in Diethyl Ether-Sodium Dioctylsulfosuccinate-Water Microemulsion System

Spherical cadmium sulfide (CdS) nanoparticles, 4–5 nm in diameter, were synthesized using an aqueous cadmium nitride [Cd(NO3)24H2O] and sodium sulfide [Na2S9H2O] solution in a microemulsion system. The effects of the water to surfactant molar ratio (W = [water]/[surfactant]), the concentration of precursors, the Cd to S precursor ratio, and the density of the ultrasonic wave on the properties of the CdS nanoparticles were examined. The luminescent properties and the size effect of the nanoparticles were characterized using UV–vis absorption and photoluminescence (PL) spectra. The PL emission intensity did not change significantly with an increase in precursor and surfactant concentrations. The absorption edge and PL peak energy of the CdS nanoparticles shifted to shorter wavelengths with an increase in cadmium nitride concentration owing to a phase change and a decrease in CdS nanoparticle size.

Synthesis and characterization of Mn, Pr doped ZnS and CdS/ZnS nanoparticles

Nanoparticles of Mn and Pr-doped ZnS and CdS-ZnS were synthesized by wet chemical method and inverse micelle method. Physical and fluorescent properties were characterized by X-ray diffraction (XRD) and photoluminescence (PL). ZnS nanoparticles annealed optically in air shows higher PL intensity than in vacuum. PL intensity of Mn and Pr-doped ZnS nanoparticles was enhanced by the photo-oxidation and the diffusion of luminescent ion. The prepared CdS nanoparticles show cubic or hexagonal phase, depending on synthesis conditions. Core-shell nanoparticles enhanced PL intensity by passivation. The interfacial state between CdS core and shell material was unchanged by different surface treatment.