Defect and Diffusion Forum Vol. 407

Abstract: The objective of this work was to provide information about the behaviour of Fe-based nanocomposites when exposed to microwaves. It is about rectangular bulk samples of epoxy resin reinforced by nanocrystalline Fe powders and shaped in accordance to the internal section of the R100 metallic waveguide (8.2 to 12.4 GHz) at a fixed thickness of 7 mm. The nanocrystalline Fe powders were obtained by high-energy mechanical milling process using a planetary Retsch PM 400-ball mill. The milling speed was fixed at 200 rpm for three durations and the milling process were performed under Argon atmosphere. The bulk nanocomposites were obtained by dispersion of 30% vol. of the nanocrystalline Fe powders in the resin matrix. Electromagnetic parameters as complex relative dielectric permittivity and magnetic permeability, electric and magnetic loss tangent and reflection loss were calculated using reordered S parameters. The scattering parameters were characterized using a measure cell made off two metallic R100 wave-guides associated to an Agilent 8719 network analyser according to the reflection-transmission technique. The obtained spectra inform on the new electromagnetic properties as well as the absorption characteristic acquired by the bulk nanocomposites due to the presence of the nanocrystalline Fe powders.

Abstract: MnZn Spinel ferrite with the chemical formula of Mn_xZn_1-xFe₂O4 (x = 0, 0.25, 0.5, 0.75, 1.0) were synthesized by a sol-gel auto-combustion method. Structural and morphological properties of synthesized samples were characterized by X-ray diffraction (XRD) and Field Emission Microscopy (FESEM). XRD patterns revealed characteristic peaks corresponding to spinel Mn-Zn ferrite structures. In addition, the structural analysis demonstrates that the average crystallite size of the synthesized samples varied in the range of 30.0-40.0 nm. The FESEM micrographs reveal agglomerated particles with particles size ranging from 60-80nm. Interfacial tension (IFT) and contact angle measurement for MnZn ferrite nanofluids were performed. The results showed that the use of MnZn ferrite nanofluid significantly decrease the oil-water IFT and contact angle.

Abstract: This research studies on the effect of additive (Dolomite) on Biomass powder (Cassava rhizome) which passes Torrefied process and fixed bed at 250 degrees Celsius for one hour and a half. The gasifier with up-draft type was used in this experiment. Air pressure was fixed at 0.1 Bar. The useful heat (Q_useful) and Low heating valves (LHV) was investigated by using an Automatic Bomb Calorimeter. Moreover, the dolomite was varied 0, 10 and 15% by weight mixed with Cassava rhizome achieved with Torrefied process. When Low heating valves (LHV) slightly decreases from 21.96±0.22 MJ/kg to 18.15±0.50 MJ/kg, Q_useful heat from the burning from gasifier sharply increase when it is mixed with dolomite from 753.34±39.18 to 1,003.97±33.49KJ respectively. The loading of dolomite has significance affecting the useful heat. The present study reveals that low heating valves (LHV) decreases and Q_useful heat increase result from dolomite which gives a clean gas product and the Tar molecule can be easily broken. The CO₂ gas from the combustion process was absorbed by CaO, which is the main component in dolomite. The cost of mixing 8.9% of Dolomite with Cassava rhizome is the optimum ratio for the biomass combustion process.

Abstract: Torrefaction process is the innovation to improve the properties of biomass. Residence time is one of the parameters that affects the properties of torrefied biomass. The residence time of a rotary kiln is the time of biomass drop into the cylinder until getting out of the cylinder. So, the propose of this study is the effect of lifters, inclination angle and rotational speed on the residence time of a rotary kiln for the torrefaction process. Palm kernel shell was used in this research. Palm kernel was chopped and minced to reduce size. The rotary kiln (0.3 meters diameter 6 meters in length) was used in this research. The number of lifters in this research were 0, 1 and 2. The rotational speed were 1, 2 and 3 rpm. The inclination angle was 1, 3 and 5 degrees. The hopper was used for the feeding system. The time was collected from biomass drop into the cylinder until getting out of the cylinder. The results reveal that the number of lifters, rotational speed and inclination angle affects the residence time of the rotary kiln. The residence time of rotary kiln was an increase when the number of lifters increase. The residence time of the rotary kiln was decreased when the rotational speed and inclination angle increase. It can be concluded that the least residence time of rotary kiln was 86.94 minute at 0 lifters, 3 rpm and 5 degrees. The most residence time was 9.22 minute at 2 lifters, 1 rpm and 1 degree.

Abstract: Theoretically, ocean waves contain enough mechanical energy to supply the entire world’s demand and, as of late, are seen as a promising source of renewable energy. To this end, several different technologies of Wave Energy Converters (WEC) have been developed such as Oscillating Water Column (OWC) devices. OWCs are characterized by a chamber in which water oscillates inside and out in a movement similar to that of a piston. This movement directs air to a chimney where a turbine is attached to convert mechanical energy. The analysis conducted was based on the Constructive Design Method, in which a numerical study was carried out to obtain the geometric configuration that maximized the conversion of wave energy into mechanical energy. Three degrees of freedom were used: the ratio of height to length of the hydropneumatic chamber (H1/L), the ratio of the height of the chimney to its diameter (H2/d) and the ratio of the width of the hydropneumatic chamber to the width of the wave tank (W/Z). A Design of Experiments (DoE) technique coupled with Central Composite Design (CCD) allowed the simulation of different combinations of degrees of freedom. This allowed the construction of Response Surfaces and correlations for the efficiency of the system depending on the degrees of freedom (width and height of the chamber), as well as the optimization of the system based on the Response Surfaces.

Abstract: Water suspension with heat transport into unsaturated-saturated porous media is analyzed. The numerical modeling includes the infiltration of silt. Moreover, the heat energy of suspension is exchanged with the heat energy of the matrix. The deposited silt influence the porosity and hydraulic permeability. The flow model is based on Richard's type equation and empirical van Genuchten - Mualem model describing capillarity driving force and saturation-pressure relation governing the flow in unsaturated part of porous media. The developed numerical method is usable for solving inverse problems determining some model parameters. The numerical method is based on flexible time discretization and a finite volume method in space variables. The nonlinearity in the flow part of the model is solved by iterative linearization based on the idea in Celia et all. The correctness of the numerical approximation is justified also by a different numerical approximation based on space discretization leading to the reduction of the whole system to the solution of ordinary differential equations. But this method requires significantly more computation time. This is not suitable for solving inverse problems. The used method is justified in numerical experiments solving the direct problem.

Abstract: This paper deals with numerical simulation and the geometrical analysis of an ocean Wave Energy Converter (WEC), which has as the operating principle the Oscillating Water Column (OWC). The goal was to evaluate the geometric shape influence of the OWC chamber in the hydropneumatic power available. Therefore, four geometric shapes were analyzed: i) Rectangle (RT), ii) Trapezium (TP), iii) Inverted Trapezium (TI) and iv) Double Trapezium (DT). For this, the OWC device was subject to a JONSWAP wave spectrum with peak period (T_S) equal to 7.5 s and peak wave height (H_S) equal to 1.5 m. To do so, Constructal Design was employed varying the Degree Of Freedom (DOF) H₁/L (ratio between the height and length of the OWC chamber entrance). The problem constraints were the entrance area and the total area of the OWC chamber that were kept constant. For the numerical solution a Computational Fluid Dynamics (CFD) code, based on the Finite Volume Method (FVM),de0 was used. The multiphase Volume of Fluid (VOF) model was applied to tackle with the water-air interaction. The results indicated that when the Rectangle (RT) geometrical shape was employed an improvement of nearly 99% was achieved.

Abstract: In this work, a flower-shaped ZnO/GO/Fe₃O₄ ternary nanocomposite was synthesized via the co-precipitation method. Two significant goals of the study were boosting the degradation efficiency of ZnO and achieving a fast and simple synthesis approach. The structure, properties, and morphology of the product were characterized, and the effect of the ZnO flower-shaped structure in combination with GO nanosheets and magnetite nanoparticles was investigated on the photocatalytic activity. The structure and quality of the prepared nanocomposite were assessed by X-ray diffraction pattern, UV-visible DRS spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM). The catalytic activity of the nanocomposite was assessed by spectrophotometric analysis. The developed nanocomposite offered high photodegradation efficiency in Rhodamine B degradation under UV-C light in comparison with pure ZnO. At a specific period, the efficiency of the synthesized sample was about two times greater than that of pristine ZnO particles. Our nanocomposite is anticipated to have practical benefits in wastewater treatment given its good performance, economic savings through reducing the amount of catalyst consumption and saving time, and being a facile and fast synthesis method.

Abstract: Absolute diffusion rates of KMnO₄ in vertical and flattened diffusimeters show the concentration gradient force as being stronger than the gravitational force. Hot water molecules move downward on self-diffusion against buoyancy. Diffusive convection (DC) in warm water and double-diffusive convection (DDC) in warm, saline water take place inside the diffusimeter with DDC transferring more heat than DC. In the diffusing medium the original reagents change or retain their compositions to give the diffusate molecules to diffuse. In water, the change is mostly hydration. The syngener BaCl₂.2H₂O separately with congeners 3CdSO₄.8H₂O, ZnSO₄.7H₂O, and ZnSO₄.H₂O presents two distinct pairs of overlapping concentration versus rate curves, first for having very close MWs of BaCl₂ and CdSO₄ and second for having ZnSO₄.H₂O as the common congener for both the zinc sulfates. Chlorides of Li, Na, and K diffusing at hindered rates in glucose solution show the least rate for LiCl inevitably on grounds of low mass and high Li⁺ hydration radius. Diffusion blocking occurs at higher glucose concentration. Diffusion of 0.6M AgNO₃-0.6M NH₄Cl standardizes this diffusimeter. Mass transfer of HCl, H₂SO₄, and H₂C₂O₄ show oxalic acid diffusing as hydrate and 88 percentage transfer of sulfuric acid in 5 minutes. The Superdiffusive Anti Graham’s Law, V_d ∝√M , is further consolidated by Ca (NO₃)₂-M₂CO₃(M = Na, K, NH₄⁺) and Ca (NO₃)₂-Na₂HPO₄ diffusions. Odd and even diffusions are illustrated by AgNO₃-NH₄Cl and AgNO₃-BaCl₂ diffusions.

Abstract: Experimental analyses are performed to determine thermal conductivity, thermal diffusivity and volumetric specific heat with transient plane source method on hollow sphere structures. Single-sided testing is used on different samples and different surfaces. Results dependency on the surface is observed.