Junhyo Kim

Surface Modification of Graphene Nanoparticles by Acid Treatment and Grinding Process.

Surface modification is necessary to decrease graphenes (GN) stacking process and increase its advantageous properties. In this study, the effects of acid treatment and grinding processes on the structural integrity of GN have been studied. Morphological and structural characteristics of modified GN were investigated by field emission scanning electron microscopy, transmission electron microscopy, gas Pycnometer, particle size analyzer, X-ray diffractometer, UV-Vis spectroscopy and thermal conductivity measurement system which expose some strong evidences of the effects of purification and grinding process on GN nanoparticles in order to get GN based better nanofluid dispersed in water which gives 1.66% and 3.38% enhancement of thermal conductivity at 20 °C and at 40 °C respectively compared to that of DW in this experiment.

Grinding characteristic of multi-walled carbon nanotubes-alumina composite particle

The synthesis of new materials containing multi-walled carbon nanotubes (MWCNTs) and the microstructure of alumina particles were investigated and characterized. The MWCNTs and alumina particles were ground under both the dry and wet conditions with various rotation speeds (200–400 r/min) in planetary ball milling machine, and their combination characteristics were described. The experimental results were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and particle sizing analysis (PSA). SEM result revealed that the combination of MWCNTs — Alumina particles mixed quite well under both the dry and wet grinding with rotation speed of 400 r/min. XRD characterization indicated the better result could get in ground samples at a rotation speed of 400 r/min. PSA result showed the particle size decreased with increase the grinding speeds. From the overall results, we observed that the grinding method can be used to synthesize new material with high efficiency.

Forced Convective Heat Transfer of Aqueous Al2O3 Nanofluid Through Shell and Tube Heat Exchanger.

This study presents the forced convective heat transfer of a nanofluid consisting of distilled water and different weight concentrations (1 wt% and 2 wt%) of Al2O3 nanoparticles flowing in a vertical shell and tube heat exchanger under counter flow and laminar flow regime with certain constant heat flaxes (at 20 °C, 30 °C, 40 °C and 50 °C). The Al2O3 nanoparticles of about 50 nm diameter are used in the present study. Stability of aqueous Al2O3 nanofluids, TEM, thermal conductivity, temperature differences, heat transfer rate, T-Q diagrams, LMTD and convective heat transfer coefficient are investigated experimentally. Experimental results emphasize the substantial enhancement of heat transfer due to the Al2O3 nanoparticles presence in the nanofluid. Heat transfer rate for distilled water and aqueous nanofluids are calculated after getting an efficient setup which shows 19.25% and 35.82% enhancement of heat transfer rate of 1 wt% and 2 wt% aqueous Al2O3 nanofluids as compared to that of distilled water. Finally, the analysis shows that though there are 27.33% and 59.08% enhancement of 1 wt% Al2O3 and 2 wt% Al2O3 respectively as compared to that of distilled water at 30 °C, convective heat transfer coefficient decreases with increasing heat flux of heated fluid in this experimental setup.