Modeling of thermal conductivity of ethylene glycol nanofluids containing carbon nanotubes by Multilayer Perceptron neural network

In our previous work [1], pristine and functionalized carbon nanotubes with 1, 2 and 4 hours refluxing times and concentrations of 0.1, 0.25 and 0.5 Vol% were used to prepare nanofluids and their thermal conductivity was measured at 20, 30, 40 and 50 °C. Lots of empirical works cannot be done because they are time consuming and costly. One of the best methods for investigation of low cost and wide range of empirical works is using the modeling methods. The artificial neural network model is a method which replicates the initial sensory processes of the brain. It is possible to design a virtual laboratory using artificial neural networks to predict the results for the same conditions even not measured experimentally. In this work, a multilayer perceptron (MLP) neural network was used to design a virtual lab and modeling the experimental data including the thermal conductivity of ethylene glycol nanofluids containing CNTs. In order to achieve a minimum error, neural networks with different hidden layers (1, 2 and 3 layers) and different number of neurons in each layer (2, 3, 4, 5, 6, 10 and 15 neurons) were studied. The minimum error of 6.5% was obtained for the neural network with two hidden layers by 3 neurons in the first layer and 2 neurons in the second one. This network was used to predict the results in the conditions which were closed to experimental conditions and it was observed that the predicted results were in good agreement with the experimental results

Carbon nanotubes length optimization for preparation of improved transparent and conducting thin film substrates

Transparent and conductive thin films of multiwalled carbon nanotubes (MWCNTs) with different lengths were prepared on glass substrates by the spin coating method. In order to reduce the MWCNTs length, they were functionalized. The initial length of MWCNTs (10–15 μm) was reduced to 1200, 205 and 168 nm after 30, 60 and 120 min refluxing time, respectively. After post annealing at 285 °C for 24 h, the electrical and optical properties were greatly improved for functionalized MWCNT thin films. They strongly depend on the length of CNTs. The optical transmittance of the film prepared using 30 min reflux CNTs was 2.6% and 6.6% higher than that of the 60 min and 120 min refluxed samples respectively. The sheet resistance of this film showed reductions of 45% and 80% as well. The film also exhibited the least roughness. The percolative figure of merit, which is proportional to the transparency and disproportional to the sheet resistance, was found to be higher for the sample with 30 min refluxed MWCNTs

Effects of initial graphite particle size and shape on oxidation time in graphene oxide prepared by Hummers' method

The effects of initial graphite particle size and shape on oxidation time of graphite prepared by Hummers' method have been investigated. The oxidation was performed on three series of graphite particles, clod powder with two different sizes of 18 and 6 μm, and flake shaped powder with an average particle size of 25 μm. The samples were characterized by means of particle size analyzer, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ratio of XRD graphite oxide peak intensity to graphite peak intensity was considered as an indicator of the oxidation degree. It was observed that the oxidation time has a critical dependence on the initial graphite particle size and shape. While the oxidation of the clod samples was completed in several days, the oxidation of flake powder was completed just in 2 h. These findings help researchers to save time by choosing the particle size and shape of initial graphite powders

The improvement of photocatalytic processes: Design of a photoreactor using high-power LEDs

This paper is an attempt to survey the benefits of a well-designed photoreactor containing just 6 ultraviolet (UV) high power light emitting diodes (HPLEDs); the power and wavelength of each UV HPLED are 1 W and 365 nm, respectively, the latter being an efficient source for photocatalytic studies. Although the experiment with the 365-nm LEDs is reported here, other LEDs were predicted for conducting similar experiments including green photocatalytic ones. We installed diodes with respect to the luminescence intensity distribution curves (LIDCs) or intensity patterns. Then, in order to compare the efficiency of the UV-HPLEDs of the HP-LED photoreactor (HPLED-PhR) with that of traditional UV lamps which are extensively used in photocatalytic processes, a set of UV HPLEDs was designed and made up. Next, the performance of HPLED-PhR was compared with that of a traditional fluorescent lamp photoreactor (FL-PhR). As a typical photocatalytic experiment, Zinc Oxide (ZnO) nanoparticles were synthesized via co-precipitation method and used as photocatalyst for purification of water polluted with the reactive blue dye (RB), under UV irradiation in two photoreactors. The results showed that the rate of photocatalytic reaction under the UV-LEDs was two times greater than the rate under the traditional fluorescent UV lamps, while both electrical power consumption and manufacturing cost of the HPLED-PhR were less than a quarter of them for the FL-PhR

Optimization and characterization of NiO thin film and the influence of thickness on the electrical properties of n-ZnO nanorods/p-NiO heterojunction

In this study, we report on the synthesis optimization of NiO thin film to grow preferentially along the (111) direction. The x-ray diffraction (XRD) pattern revealed that the NiO film with 200 nm thickness annealed at 600 degrees C temperature has the best preferential orientation along the (111) direction. Also, atomic force microscope (AFM) images show that the grain size of NiO increases at higher temperatures. Then, ZnO nanorods were grown on the NiO thin film with 100, 200 and 300 nm thickness grown at 600 degrees C. The XRD pattern and scanning electron microscope (SEM) images indicate that the well-aligned ZnO nanorods with hexagonal face have a preferential orientation along the c-axis (002). The current voltage measurements of the n-ZnO nanorods/p-NiO heterojunctions showed a clear rectifying behavior for all diodes. The threshold voltage of the heterojunctions was increased by increasing the thickness of the NiO thin film which was attributed to the increasing of the series resistance (R-s) of the diodes.Funding Agencies|Linkoping University; Shahid Chamran university of Ahvaz</p