Thermal conductivity modeling of MgO/EG nanofluids using experimental data and artificial neural network

The application of nanofluids in energy systems is developing day by day. Before using a nanofluid in an energy system, it is necessary to measure the properties of nanofluids. In this paper, first the results of experiments on the thermal conductivity of MgO/ethylene glycol (EG) nanofluids in a temperature range of 25–55 °C and volume concentrations up to 5 % are presented. Different sizes of MgO nanoparticles are selected to disperse in EG, including 20, 40, 50, and 60 nm. Based on the results, an empirical correlation is presented as a function of temperature, volume fraction, and nanoparticle size. Next, the model of thermal conductivity enhancement in terms of volume fraction, particle size, and temperature was developed via neural network based on the measured data. It is observed that neural network can be used as a powerful tool to predict the thermal conductivity of nanofluids.     

Heat transfer and rheological properties of transformer oil-oxidized MWCNT nanofluid

Power transformers play a key role in power and electrical industries and thus boosting their efficiency is necessary. In this study, the effect of oxidized multi-walled carbon nanotubes on transformer oil thermophysical properties was experimentally investigated. The maximum amount of carbon nanotubes was chosen up to 0.01 mass% to assure the maximum purity of transformer oil. Heat transfer characteristics of transformer oil and nanofluids in two cases of free and forced convection were studied. Breakdown voltage, flash point, pour point, density, electrical and thermal conductivities, viscosity and shear stress, as eight important quality parameters, were determined. According to the experimental results, the Breakdown voltage decreased through concentration increasing. Electrical conductivity is not changed considerable with increasing concentration and temperature. Thermal conductivity of nanofluids and transformer oil changed with increasing temperature and concentration. Furthermore, at all concentrations and temperatures, the viscosity of the nanofluids was lower than that of transformer oil.     

Electrochemical preparation of α-Ni(OH)2 ultrafine nanoparticles for high-performance supercapacitors

Well-dispersed nanoparticles of nickel hydroxide were prepared via a simple electrochemical method. Electrodeposition experiments were performed from 0.005 M Ni(NO₃)₂ bath at a constant current density of 0.1 mA cm^?2 on the steel cathode for 1 h. Recording the potential values during the deposition process revealed that the reduction of water has major role in the base electrogeneration at the applied conditions. The obtained deposit was characterized by the X-ray diffraction (XRD), infrared (IR), differential scanning calorimeter–thermogravimetric analysis, carbon–nitrogen–hydrogen (CHN), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The CHN, XRD, and IR analyses showed that the obtained deposit has α phase of Ni(OH)₂ with intercalated nitrate ions in its structure. Morphological characterization by SEM and TEM revealed that the prepared α-Ni(OH)₂ is composed of well-dispersed ultrafine particles with the size of about 5 nm. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry and galvanostatic charge–discharge tests. The electrochemical measurements showed an excellent supercapacitive behavior of the prepared α-Ni(OH)₂ nanoparticles. It was also observed that the α-Ni(OH)₂ ultrafine particles have better electrochemical characteristic and supercapacitive behavior than β-Ni(OH)₂ ultrafine nanoparticles, including less positive charging potential, lower E _a???E _c value, better reversibility, higher E _OER???E _a, higher utilization of active material, higher proton diffusion coefficient, greater discharge capacity, and better cyclability. These results make the α-Ni(OH)₂ nanoparticles as an excellent candidate for the supercapacitor materials.     

Comparison and Evaluation of Three Diagnostic Methods for Detection of Beet Curly Top Virus in Sugar Beet Using Different Visualizing Systems

To diminish the time required for some diagnostic assays including polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP; due to mainly DNA extraction step) and also triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) into a minimum level, an innovative immunocapture LAMP (IC-LAMP) and immunocapture PCR (IC-PCR) protocol on the basis of beet curly top virus (BCTV) genome was used and optimized. TAS-ELISA was employed first to validate the existence of the virus. All six IC-LAMP primers (i.e. forward outer primer (F3), backward outer primer (B3), forward inner primer (FIP), backward inner primer (BIP), loop forward (LF) and loop backward (LB)) together with IC-PCR primers were designed on the basis of the replication-associated protein (rep) gene (GenBank accession AF379637.1) of BCTV genome. Also, a novel colorimetric IC-LAMP assay for rapid and easy detection of BCTV was developed here, its potential compared with TAS-ELISA and IC-PCR assays. The method, on the whole, had the following advantages over the two mentioned procedures: (i) fascinatingly, no need of DNA extraction; (ii) no requirement of expensive and sophisticated tools for amplification and detection; (iii) no post-amplification treatment of the amplicons and (iv) a flexible and easy detection approach, which is visually detected by naked eyes using diverse visual dyes.     

Selective complexation of alkali metal ions and nanotubular cyclopeptides: a DFT study

A density functional theory based on interaction of alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) with cyclic peptides constructed from 3 or 4 alanine molecule (CyAla3 and CyAla4), has been investigated using mixed basis set (C, H, O, Li⁺, Na⁺ and K⁺ using 6-31+G(d), and the heavier cations: Rb⁺ and Cs⁺ using LANL2DZ). The minimum energy structures, binding energies, and various thermodynamic parameters of free ligands and their metal cations complexes have been determined with B3LYP and CAM-B3LYP functionals. The order of interaction energies were found to be Li⁺ > K⁺ > Na⁺ > Rb⁺ > Cs⁺ and Li⁺ > Na⁺ > K⁺ ? Rb⁺ > Cs⁺, calculated at CAM-B3LYP level for the M/CyAla3 and M/CyAla4 complexes, respectively. Their selectivity trend shows that the highest cation selectivity for Li⁺ over other alkali metal ions has been achieved on the basis of thermodynamic analysis. The main types of driving force host–guest interactions are investigated, the electron-donating O offers lone pair electrons to the contacting LP* of alkali metal cations.     

Exo/endo stereocontrolled synthesis of spiroindoloindolizidines by using classical and microwave conditions via the 1,3-dipolar cycloaddition reaction

Using both classical reflux and microwave-mediated conditions, a series of new spiroindoloindolizidines was synthesized by multicomponent 1,3-dipolar cycloaddition of azomethine ylides in unprecedented exo/endo stereocontrolled. Both conditions easily afforded two identical and separable exo/endo diastereomeric ratios of cycloadducts. However, the ratio of two diastereomeric products obtained from conventional conditions was reversed in all examined cases when the reactions were explored under microwave-mediated conditions. As expected, utilizing the microwave-assisted conditions produced higher yields and reaction rates compared to classical conditions. The structure and exact stereochemistry of synthesized cycloadducts were determined by applying various 2D-NMR spectroscopic techniques and single-crystal X-ray diffraction. Finally, the mechanism of the reaction has been briefly investigated by using density functional theory (DFT) calculations.     

Rapid and green synthesis of 4H-benzo[b]pyrans using triethanolamine as an efficient homogeneous catalyst under ambient conditions

Research on Chemical Intermediates - 4H-benzo[b]pyrans were obtained rapidly in high yields using triethanolamine as an efficient, eco-friendly and low-cost basic catalyst. One-pot three-component...     

Experimental design for estimation of the distribution of the convective heat transfer coefficient for a bubbly impinging jet

Journal of Thermal Analysis and Calorimetry - In this study, a two-dimensional inverse algorithm is developed to determine the heat transfer coefficient distribution of a two-phase air–water...     

Hybrid thermal management of lithium-ion batteries using nanofluid,metal foam,and phase change material: an integrated numerical–experimental approach

Safety issues of Li-ion batteries imposed by unfavorable thermal behavior accentuate the need for efficient thermal management systems to prevent the runaway conditions. To that end, a hybrid thermal management system is designed and further investigated numerically and experimentally in the present study. The passive cooling system is fabricated by saturating copper foam with paraffin as the phase change material (PCM) and integrated with an active cooling system with alumina nanofluid as the coolant fluid. Results for various Reynolds numbers and different heating powers indicate that the hybrid nanofluid cooling system can successfully fulfill safe operation of the battery during stressful operating conditions. The maximum time in which all PCM field is changed to the liquid phase is defined as the onset of the stressful conditions. Therefore, the start time of stressful conditions at 41 W and Re 420 is increased from 3700 s with nanofluid composed of 1% volume fraction nanoparticles (VF-1%) to 4600 s with nanofluid VF-2% during high current discharge rates. Nanofluid cooling extends the operating time of the battery in comparison with the water-based cooling system with 200-s (nanofluid with volume fraction of 1%) and 900-s (nanofluid with volume fraction of 2%) increases in operating time at Reynolds of 420. Using nanofluid, instead of water, postpones the onset of paraffin phase transition effectively and prolongs its melting time which consequently leads to a decrease in the rate of temperature rise.

     

Robust fixed-time attitude stabilization control of flexible spacecraft with actuator uncertainty

Nonlinear Dynamics - A robust fixed-time control framework is presented to stabilize flexible spacecraft’s attitude system with external disturbance, uncertain parameters of inertia, and...