Pham Van Trinh

Enhanced thermal conductivity of nanofluid-based ethylene glycol containing Cu nanoparticles decorated on a Gr–MWCNT hybrid material

In this study, nanofluid based ethylene glycol (EG) containing Cu nanoparticles decorated on a Gr–MWCNT hybrid material (Gr–MWCNT/Cu) was synthesized successfully for the first time via a chemical reduction method. The SEM, HRTEM, FTIR and XRD studies revealed that Cu nanoparticles with an average diameter of 18 nm were well decorated on the surface of both MWCNTs and graphene sheets. The nanofluids containing Gr–MWCNT/Cu material showed good stability and a maximum thermal conductivity enhancement of 41% at 60 °C for the nanofluid containing 0.035 vol% material compared to EG alone. The enhancement is due to the combination of the high thermal conductivity of graphene, CNT and Cu nanoparticles as well as the higher surface area of the Gr–MWCNT/Cu hybrid structure. Experimental results of thermal conductivity were evaluated using different theoretical models, amongst which the Hamilton–Crosser model was found suitable for predicting the thermal conductivity of the nanofluid.

Heat Dissipation for Microprocessor Using Multiwalled Carbon Nanotubes Based Liquid

Carbon nanotubes (CNTs) are one of the most valuable materials with high thermal conductivity (2000 W/m · K compared with thermal conductivity of Ag 419 W/m · K). This suggested an approach in applying the CNTs in thermal dissipation system for high power electronic devices, such as computer processor and high brightness light emitting diode (HB-LED). In this work, multiwalled carbon nanotubes (MWCNTs) based liquid was made by COOH functionalized MWCNTs dispersed in distilled water with concentration in the range between 0.2 and 1.2 gram/liter. MWCNT based liquid was used in liquid cooling system to enhance thermal dissipation for computer processor. By using distilled water in liquid cooling system, CPUs temperature decreases by about 10°C compared with using fan cooling system. By using MWCNT liquid with concentration of 1 gram/liter MWCNTs, the CPUs temperature decreases by 7°C compared with using distilled water in cooling system. Theoretically, we also showed that the presence of MWCNTs reduced thermal resistance and increased the thermal conductivity of liquid cooling system. The results have confirmed the advantages of the MWCNTs for thermal dissipation systems for the μ-processor and other high power electronic devices.

Influence of defects induced by chemical treatment on the electrical and thermal conductivity of nanofluids containing carboxyl-functionalized multi-walled carbon nanotubes

In this paper, we present the results on the influence of chemical treatment time on the structure of carboxyl-functionalized MWCNTs (MWCNT–COOH) and their nanofluids. The morphological and structural studies investigated by FTIR, HRTEM and Raman scattering demonstrated that the structural defects of MWCNT–COOH increase with increasing chemical treatment time. Nanofluids containing MWCNT–COOH treated for a longer time showed better stability due to the increasing of COOH functional groups attached to the surface of MWCNTs. The electrical conductivity of the nanofluids increases with increasing CNT concentration and decreases with increasing chemical treatment time. The thermal conductivity of the nanofluids enhanced when increasing CNT concentration and reached the highest value for MWCNT–COOH with 5 h chemical treatment. By using the effective medium theory (EMT) and experimental data fitting, the thermal boundary resistance (TBR) and the thermal boundary conductance (TBC) of MWCNT–COOH/water were found to be 90 × 10−8 m2 K W−1 and 1.1 MW m−2 K−1, respectively. The interfacial layer thermal conductivity (Ki) between CNTs and base fluid was estimated by using Mursheds model. The highest Ki was obtained to be 2.6 W m−1 K−1 for a nanofluid with 5 h chemical treatment. The results implied that the thermal conductivity of CNT based nanofluids could be improved by increasing the Ki via optimizing of the chemical treatment conditions.

Effect of Surface Morphology and Dispersion Media on the Properties of PEDOT:PSS/n-Si Hybrid Solar Cell Containing Functionalized Graphene

We present the results on the effect of surface morphology and dispersion media on the properties of PEDOT:PSS/n-Si hybrid solar cell containing functionalized graphene (Gr). The hybrid solar cells based on SiNWs showed higher power conversion efficiency (PCE) compared to the planar based cells due to suppressing the carrier recombination and improving carrier transport efficiency. The PCE of hybrid solar cells could be improved by adding Gr into PEDOT:PSS. Different solvents including deionized (DI) water, ethylene glycol (EG), and isopropyl alcohol (IPA) were used as media for Gr dispersion. The best performance was obtained for the cell containing Gr dispersed in EG with a measured PCE of 7.33% and nearly 13% and 16% enhancement in comparison with the cells using Gr dispersed in IPA and DI water, respectively. The increase in PCE is attributed to improving the carrier-mobility, electrical conductivity, PEDOT crystallinity, and ordering.

Fabrication, microstructure, and microhardness of copper composites reinforced by carbon nanotubes

Composites with a copper matrix, reinforced by carbon nanotubes, have been produced by the multistage method including functionalization of carbon nanotubes, their dissolution, mixing with a copper powder, preliminary warm isostatic compaction, and severe plastic deformation by torsion. The microstructure and microhardness of composites containing to 4 wt % of carbon nanotubes have been studied. It has been shown that the matrix grain size after severe plastic deformation significantly decreases, while the internal stress level, dislocation density, and composite microhardness increase with increasing concentration of nanotubes.

Effect of Annealing Time on the Power Conversion Efficiency of Silicon Nanowire Based Solar Cell Prepared by Wet Diffusion Technique

1 Institute of Materials Science, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam 2 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam 3 Center for High Technology Development, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam

Thermal Conductivity of Ethylene Glycol Based Copper Nanoparticle Decorated Graphene Nanofluids

In this paper, thermal conductivity of ethylene glycol based copper nanoparticle decorated graphene (Cu/Gr) nanofluids are successfully synthesized by a chemical reduction technique using ascorbic acid antioxidant agent. Nano-sized copper nanoparticles are decorated on functionalized graphene, and then dispersed uniformly in ethylene glycol (EG) to make the nanofluids. Morphology, phase composition and thermal conductivity of nanofluids are investigated in detail. Thermal conductivity of the nanofluid containing Cu/Gr with mass ratio of 5:1 shows an enhancement about 10% and 29% at 30 ̊C and 60 ̊C comparing with the EG fluid only. The results show the high potential application of Cu/Gr nanofluids in heat transfer fields.