Bui Hung Thang

A modified model for thermal conductivity of carbon nanotube-nanofluids

Carbon nanotubes (CNTs) are one of the most valuable materials with high thermal conductivity (above 1750 W/m K compared to thermal conductivity of Ag 419 W/m K). Owing to their very high thermal conductivity, CNTs are one of the most suitable nanoadditives in fabricating the nanofluid with thermal conductivities that are significantly higher than those of the parent liquids even when the CNTs’ concentrations are negligible. This work presents a modified model for predicting the thermal conductivity of carbon nanotube-nanofluids (CNT-nanofluids), which take into consideration the effects of size, volume fraction, and thermal conductivity of CNTs as well as the properties of base liquid. The modified model is found to correctly predict the trends observed in experimental data for different combinations of CNT-nanofluids with varying concentrations.

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.

Application of multiwall carbon nanotubes for thermal dissipation in a micro-processor

One of the most valuable properties of the carbon nanotubes materials is its high thermal conductivity with 2000 W/m.K (compared to thermal conductivity of Ag 419 W/m.K). It suggested an approach in applying the CNTs in thermal dissipation media to improve the performance of computer processors and other high power electronic devices. In this research, the multiwall carbon nanotubes (MWCNTs) made by thermal chemical vapour deposition (CVD) at our laboratory was employed as the heat dissipation media in a microprocessor a Personal Computer with configuration: Intel Pentium IV 3.066 GHz, 512Mb of RAM and Windows XP Service Pack 2 Operating System. We directly measured the temperature of the microprocessor during the operation of the computer in two modes: 100% usage CPU mode and over-clocking mode. The measured results showed that when using our thermal dissipation media (a mixture of the mentioned commercial thermal compound and 2 wt.%. MWCNTs), the temperature of the microprocessor decreased 5°C, and the time for increasing the temperature of the microprocessor was three times longer than that when using commercial thermal compound. In over-clocking mode, the processor speed reached 3.8 GHz with 165 MHz of system bus clock speed; it was 1.24 times higher than that in non over-clocking mode. The results confirmed a promising way of using MWCNTs as the thermal dissipation media for microprocessor and 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.

Electron field emission characteristics of carbon nanotube on tungsten tip

Electron field emission characteristic of carbon nanotubes on tungsten tip was investigated in 2?10-6 Torr vacuum. The measurement results showed that the CNTs/W tip could emit electron at 0.7 V/?m (nearly 10 times lower than that of the W tip itself) and reach up to 26 ?A at the electric field of 1 V/?m. The emission characteristic follows the Fowler-Nordheim mechanism. Analysis of the emission characteristic showed that the CNTs/W tip has a very high value of field enhancement factor (? = 4.1 ? 104 cm-1) that is much higher than that of the tungsten tip itself. The results confirmed the excellent field emission behavior of the CNTs materials and the CNTs/W tip is a prospective candidate for advanced electron field emitter.

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.

Carbon nanotubes based lubricating oils for engines

Carbon nanotubes (CNTs) are well-known nanomaterials with many excellent properties such as high hardness, high strength, and excellent thermal conductivity. Owing to their very high thermal conductivity (2000 W/m.K compared to thermal conductivity of Ag 419 W/m.K), CNTs become ones of the most suitable nano additives for fabricating the lubricating oils in order to increase the thermal conductivity of lubricating oils, to enhance the efficiency of heat dissipation for the engine, and to improve the performance efficiency of engine. In this work, we present the obtained results on application of the CNTs in lubricating oils for some engines. The results showed that with the addition of CNTs, the thermal conductivity of lubricating oils increase about 15%, this helps improve the efficiency of heat dissipation for the engine. Experimental results show that when using the lubricating oils containing carbon nanotubes, the temperature of engine dropped about 10°C, fuel saving was upto 15% and longevity of lubricating oil increased upto 20,000 km.

Thermal Dissipation Efficiency in a Micro‐Processor Using Carbon Nanotubes Based Composite

Modern electronic and optoelectronic devices such as μ‐processor, light emitting diode, semiconductor laser issued a challenge in the thermal dissipation problem. Finding an effective way for thermal dissipation therefore becomes a very important issue. It is known that carbon nanotubes (CNTs) is one of the most valuable materials with high thermal conductivity (2000 W/m.K compared to thermal conductivity of Ag 419 W/m.K). This suggested an approach in applying the CNTs as an essential component for thermal dissipation media to improve the performance of computer processor and other high power electronic devices. In this work multi walled carbon nanotubes (MWCNTs) based composites were utilized as the thermal dissipation media in a micro processor of a personal computer. The MWCNTs of different concentrations were added into polyaniline, commercial silicon thermal paste and commercial silver thermal paste by mechanical methods. A personal computer with configuration: Intel Pentium IV 3.066 GHz, 512 MB of ...

NICKEL-BASED MULTIWALLED CARBON NANOTUBE COMPOSITE COATINGS

Carbon nanotubes (CNTs) have been widely known as nanomaterials with excellent mechanical properties. Previous studies reported that the tensile strength of multi-walled carbon nanotubes (MWCNTs) was up to 63 GPa and single-walled carbon nanotubes (SWCNTs) could reach 150 GPa while the highest tensile strength of the steel was found to be about 1.8 GPa. SWCNTs could have Young’s modulus up to 1000 GPa that was much greater than the value of 209 GPa of steel. Therefore, there is a great potential to utilize CNTs as reinforced materials for composites in general and Ni electrodeposition coating in particular to improve hardness, durability, corrosion, and other physical and mechanical properties. This paper presents results of preparing and examining characteristics of the Nickel electrodeposition coatings containing MWCNTs (Ni-MWCNTs). The Ni-MWCNTs composite coatings deposited on a steel plate with the area of 0.4 dm 2 using bipolar pulses at 470 Hz and 50 o C in a 5-liter bath. Amount of CNTs varying from 1 g/l to 3 g/l was dispersed into the solution by using surfactants and ultrasonic vibration. CNTs used in the study was MWCNTs diameters in the range from 20 to 90 nanometers and few micrometers in length. The SEM, EDS, hardness and adhesion tests were conducted to analyze the properties of the electrodeposition coatings. The obtained results indicated that the hardness and adhesion of the Ni-CNTs coating were 1.5 and 1.46 times, respectively, higher than those of the Ni coating. In addition, adhesion of the Ni-CNTs coating was significantly improved.