Activation Energy Model Research Articles

New insights into the dynamics of heat and mass transfer in a hybrid (Ag-TiO[formula omitted]) nanofluid using Modified Buongiorno model: A case of a rotating disk

The activation energy model is used in this work to examine how hybrid nanoparticles affect the flow across a rotating disk. Here, we considered nanoparticles of silver (Ag) and titanium dioxide (TiO2) dissolved in water, a base liquid. These nanoparticles have real applications such as photography, photocatalysis, water purification, and solar energy conversion. The current study investigates the combined effects of a changing magnetic field, Darcy Forchheimer, porosity, thermal radiation, Brownian motion, and thermophoresis on hybrid nanofluid flow across a rotating disk. By applying similarity transformations, the partial differential equations system of the current scheme is converted into an ordinary differential equations system, after which it is calculated with MATLAB using the bvp4c scheme. Graphs are used to assess the investigation of mass and heat transport. Also, the change in concentration, temperature, and velocity profiles for various non-dimensional factors are discussed briefly using corresponding graphs. It has been noted that the velocity gradient of mono and hybrid nanofluids is reduced as the magnetic parameter inputs increase. The velocity profiles decline as the input of the Darcy-Forchheimer parameter increases. The outcome demonstrates that temperature and concentration increase as the thermophoresis parameter rises. The concentration profile is enhanced as an activation energy parameter increases. Moreover, the average Nusselt number is 37.73 % at M=0.8, and when M=2.2, the value of the average number decreased by 29.43 %. The concentration of silver (Ag) and titanium dioxide (TiO2) is (0−6)%.

Stability of Cu(InxGa1−x)Se2 Solar Cells Utilizing RbF Postdeposition Treatment under a Sulfur Atmosphere

Alkali halide postdeposition treatments (PDTs) have become a key tool to maximize efficiency in Cu(InxGa1−x)Se2 (CIGS) photovoltaics. RbF PDTs have emerged as an alternative to the more common Na‐ and K‐based techniques. This study utilizes temperature‐dependent current–voltage (JVT) measurements to study a unique RbF PDT performed in a S atmosphere. The samples are measured before and after 6 months in a desiccator to study device stability. Both samples contain Na and K which diffuse from the soda–lime glass substrate. A reference sample and a RbF + S PDT sample both show the development of a rear contact barrier after aging. The contact barrier is higher for the RbF + S PDT sample, leading to decreased current in forward bias. Series resistance is also higher in the RbF + S PDT device which leads to lower fill factor. However, after aging the reference sample has a larger decrease in open‐circuit voltage (VOC). Ideality factor measurements suggest Shockley–Read–Hall recombination dominates both samples. VOC versus temperature and a temperature‐dependent activation energy model are used to calculate diode activation energies for each sample condition. Both techniques produce similar values that indicate recombination primarily occurs within the bulk absorber.

Introducing field evaporation energy loss spectroscopy

Retrieving information on the chemical and bonding states of atoms in a material in three-dimensions is challenging even for the most advanced imaging techniques. Here, we demonstrate that this information is accessible via straight-flight-path atom probe tomography experimental data, however it requires additional processing. Using an activation energy model that involves linear field dependance, and complementing it with DFT simulations, we extract the ion energy loss related to the kinetics of the field evaporation process from the mass peak shape. In turn, we reconstruct how evaporated atoms were originally bound to the surface. We name our data processing approach evaporation energy loss spectroscopy (FEELS), and showcase its application by analyzing microstructural features and defects in an array of metallic materials. Finally, we discuss the general applicability of FEELS to any atom probe data set.

Magnesium Chloride Crystals with Studying Mechanism and Leaching Kinetics of Serpentinite Ore by Hydrochloric Acid

Magnesium chloride hexahydrate crystal (MgCl2.6H2O) is an intermediate product used to obtain Mg metal from its ores. This work aims to produce purified MgCl2.6H2O crystals from natural Egyptian serpentine. Serpentine samples were collected from the Eastern Desert in Egypt and prepared for leaching with HCl solutions. Reaction temperature (°C), leaching time (h), solid/liquid ratio (g/mL), and acid concentration (M) were studied. The optimum leaching conditions achieved 97.6% MgO recovery optimized at particle size less than 75 µm (100%), 95 °C of the reaction temperature for three hours with solid-to-liquid ratio 1:5, and 5 M of HCl concentration. The serpentine dissolution kinetics were studied depending on the solid–liquid reaction and activation energy model. The resultant liquor was purified and crystallized. The kinetic studies indicated that product layer diffusion is the most likely rate-controlling step for serpentinite dissolution in the HCl solution.

Kinetic analysis and modeling of maize straw hydrochar combustion using a multi-Gaussian-distributed activation energy model

Kinetic analysis and modeling of maize straw hydrochar combustion using a multi-Gaussian-distributed activation energy model

Magnetohydrodynamic flow and heat transfer of a hybrid nanofluid over a rotating disk by considering Arrhenius energy

This research work explores the effect of hybrid nanoparticles on the flow over a rotating disk by using an activation energy model. Here, we considered molybdenum disulfide and ferro sulfate as nanoparticles suspended in base fluid water. The magnetic field is pragmatic normal to the hybrid nanofluid flow direction. The derived nonlinear ordinary differential equations are non-dimensionalized and worked out numerically with the help of Maple software by the RKF-45 method. The scientific results for a non-dimensionalized equation are presented for both nanoparticle and hybrid nanoparticle case. Accoutrements of various predominant restrictions on flow and thermal fields are scanned. Computation estimation for friction factor, local Nusselt number and Sherwood number are also executed. Results reveal that the reduction of the heat transfer rate is greater in hybrid nanoparticles when compared to nanoparticles for increasing values of Eckert Number and the thermal field enhances for the enhanced values of volume fraction.

DAEM kinetics analysis and finite element simulation of thermal debinding process for a gelcast SiAlON green body

Thermal debinding is an important step in a gelcasting process, and the proper selection of the debinding technique is crucial for the quality of a green body. In this work, the pyrolysis characteristics of an N,N-dimethylacrylamide/N,N′-methylenebisacrylamide gel system in a thermal debinding process of a gelcast SiAlON green body were investigated through nonisothermal thermogravimetric analysis and a thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy analysis. In addition, the pyrolysis kinetics of the thermal debinding process of the gelcast SiAlON green body were described by using a three-parallel-distributed activation energy model. The results showed that the conversion (α) and reaction rate (dα/dT) curves predicted by the kinetic model agreed well with the experimental data. The kinetic parameters (E0,i, k0,i, and σi) of the global thermal debinding process were 116.0–158.0 kJ/mol, 9.31 × 108 s−1 and 2.19–20.52 kJ/mol, respectively. Finally, a solid–fluid–thermal–mechanical coupling numerical model of the thermal debinding process was established through finite element methods on the basis of theories of the porous medium seepage and thermodynamics. The distributions of the residual content of the gel polymer, the temperature, the pressure, and the stress in the green body throughout the entire thermal debinding process were evaluated using this model. It was shown that a high heating rate leads to a high temperature gradient and von Mises stress inside the green body. Moreover, a reasonable debinding technique was proposed to effectively prevent and eliminate defects caused by excessive stress or a temperature gradient inside the green body. In a given DMAA/MBAM gel system, the strongest stress peak can be effectively eliminated by holding at 310 °C for no less than 2 h at a heating rate of 1 °C/min. This work aims to provide a theoretical basis for studying thermal debinding kinetics and optimizing debinding techniques for the gelcasting of various materials.

Kinetics study on non-isothermal crystallization of Ni1.5MnSn0.5Co alloy thin films

ABSTRACTThe crystallization kinetics of the Ni1.5MnSn0.5Co free-standing alloy thin films is investigated by continuous heating differential scanning calorimetry (DSC). The results show that all the DSC traces have a single exothermic peak, with a long high temperature tail. The DSC curves have been analyzed in terms of activation energy and kinetic model. We find that the activation energy of film obtained by both the Kissinger and Ozawa equation methods can give consistent results, the activation energy for crystallization is determined as 221.2 and 220.9 KJ/ mol, respectively. Moreover, the volume fraction crystallized has significantly influence on the local activation energy, and the regular of the nucleation and growth of films has been changed at crystallization process. Our work would enrich the mechanism of the crystallization kinetics for annealing applications of Ni-Mn-Sn-Co thin films in microelectro mechanical systems (MEMS).

Hybrid and Fluid Modeling of Ion Activation Energy and Reactive Fluxes to Particulates Suspended in Air and Residing on Surfaces

We report on a computational study of the intersection of plasma filaments in a dielectric barrier discharge with small particulates suspended in air or residing on surfaces. The relative location of the particle with respect to the streamer axis is important on plasma time scale considered in the paper. The particulates residing on the substrate surface are partially enveloped by the sheath formed beneath the filament and the substrate. Ion energies and fluxes incident on the particulate depend on dielectric properties of the underlying substrate materials.

Electron transfer from organic dyes to reduced graphene oxide studied by photoluminescence spectroscopy

Reduced graphene oxide (rGO) sheets are widely used as electron acceptors in energy‐conversion processes and optoelectronic devices. Therefore, it is of great significance to research the electron transfer (ET) between dyes and rGO. Herein, steady‐state and time‐resolved photoluminescence (PL) spectra of Rhodamine B (RhB) in the presence of rGO at different temperatures were measured. At low ratios of RhB to rGO, the emission kinetics reveals that ca. 37.22% of the electrons at excited states of RhB transfer to rGO at room temperature. Also, with the temperature rising, the ET rate slows down while the amount of transferring electrons first increases then decreases. The process of the ET matches well with the Marcus theory of electron–vibration coupling. At high ratios of RhB to rGO, the ET is explained by the model of activation energy. The ET occurs faster at higher temperature.

Photosynthetic characteristics and inferred changes in thylakoid membrane fluidity determine bloom succession between Anabaena and Microcystis in eutrophic lakes

Anabaena and Microcystis are common dominant cyanobacterial genera and frequently form blooms in large shallow eutrophic lakes in China. There is usually a quick succession between these two cyanobacterial blooms in early summer; however, there is currently no solid evidence based on photosynthesis and population competition to explain this phenomenon. This study compared the photosynthetic parameters and the indirectly measured thylakoid membrane fluidity characteristics between Anabaena and Microcystis. The results showed that the growth rate, the maximum photochemical efficiency of PSII (F v/F m), and the maximum relative electron transport rate (r ETR max) of Microcystis cultured at 25 °C were significantly lower than those from cells grown at 15 °C, indirectly suggesting a marked limitation of thylakoid membrane fluidity at low temperatures. Chlorophyll fluorescence dynamics also indicated inhibition of NPQ formation and membrane fluidity when Microcystis was cultured at low temperatures; however, this inhibition was not significant for Anabaena. Fourier transition infrared (FT-IR) spectrometry indicated that the thylakoid membrane of Anabaena can maintain homeostasis fluidity through the upregulation of unsaturated fatty acids when exposed to chilling stress. Increasing the temperature significantly promoted the growth rate of Microcystis, while it had little effect on Anabaena. Moreover, photoinhibition of Anabaena was more easily induced by high light, thus accelerating the bloom succession from Anabaena to Microcystis during warm seasons. An activation-energy model was used to deduce that the threshold temperature of bloom succession was 15.4 °C, which would increase to 16.2 °C and decrease to 14.9 °C under conditions of N-limitation and P-limitation.

A Combined Quantum Mechanics and Molecular Mechanics Study on Nitrogen Oxide Adsorption/Dissociation on a Tungsten Oxide Surface

The kinetics and mechanism of the adsorption and dissociation of nitrogen monoxide (NO) into N2 and O2 molecules on a tungsten oxide nanocrystalline surface have been studied. Calculations were carried out using the framework of density functional theory (DFT) with the ONIOM method at the (B3LYP/LANL2DZ:UFF) level. In this study, four models of the dissociation have been proposed and investigated theoretically. Density of states (DOS) spectral analysis showed that the Fermi level is shifted to higher values and confirmed the effective interaction between the nanocrystal and adsorbate. The band gap is also reduced after adsorption. Quantum reactivity indices showed that the chemical hardness was reduced after adsorption, which corresponds to the reduction in band gap. The electronic chemical potential has been shifted to more positive values while the electrophilicity of the surface has been reduced, both after adsorption. These parameters predict that charge transfers to the surface. Considering the activation energy, the first and second proposed models provide the most probable route of NO decomposition. Finally, from a comparison between the decomposition and oxidation processes, it is confirmed that NO oxidation is preferred.

Effects of Soret Diffusion on Premixed Counterflow Flames

Soret diffusion is a secondary mass diffusion and it affects laminar flames with very light or heavy species and large temperature gradients. To get a general understanding of Soret effects on stretched flames, we conduct theoretical analysis on a premixed counterflow flame with Soret diffusion. A deliberately idealized premixed counterflow flame model is analyzed asymptotically within the framework of large activation energy, potential flow, and thermal-diffusive model. A correlation among flame stretch rate, flame position, and flame temperature is derived and is used to assess the effects of Soret diffusion on counterflow flame structure, Markstein length, and extinction stretch rate. Results show that Soret diffusion quantitatively affects the premixed counterflow flame and that the influence of Soret diffusion strongly depends on Lewis number and stretch rate. For light fuels, the premixed counterflow flame becomes stronger after including Soret diffusion. The opposite trend occurs for heavy fuels. The influence of Soret diffusion is found to increase with the stretch rate. A linear change between normalized Markstein length and Soret diffusion coefficient is observed, indicating that flame becomes more sensitive to stretch rate after including Soret diffusion. Furthermore, Soret diffusion is shown to greatly increase the extinction stretch rate of light fuels. These results indicate that for highly-stretched premixed flames containing very light species, the impact of Soret diffusion cannot be neglected.

Effective Moisture Diffusivity, Activation Energy and Dielectric Model for Palm Fruit Using a Microwave Heating

A microwave heating process for palm fruit can quickly remove the moisture content and destroy any free fatty acids (FFA) in palm fruit. In this paper, the key parameters for palm fruit to design an effective microwave heating system, effective moisture diffusivity, activation energy and dielectric model are reported. These parameters can predict the temperature distribution and moisture ratio in var. Tenera palm fruit when using a 2.45 GHz microwave, heating at four different power levels (160, 320, 480, 800 W). By assuming that each palm layer is homogeneous, a model composed of physical layers (mesocarp, shell and kernel) was developed. The effective moisture diffusivity of the palm fruit is determined by Fick’s second law for mass transport mechanism. The calculated value of the effective moisture diffusivity of the palm fruit increases with the temperature since the water molecules in the palm fruit diffuses quickly at high temperature. In addition, the activation energy of palm fruit ranges from 31.06 to 48.91 kJ(mol)-1 with the different microwave powers, which were obtained by applying the linear regression technique to the Arrhenius equation model. Finally, the comparisons between the computed and the actual experiment for the moisture ratio with the different microwave powers were computed from the effective moisture diffusivity in the palm fruit. The results obtained from both data sets highly correlate.

The interrelated effect of activation energy and grain boundary energy on grain growth in nanocrystalline materials

Abstract The interrelated effect of activation energy and grain boundary energy on grain growth and thermal stabilization in nanocrystalline materials was investigated. Departing from Borisov's equation and Kirchheim's grain boundary energy model, an activation energy model was derived incorporating solute segregation and grain growth. An integrated thermokinetic model for nanoscale grain growth was then developed by incorporating the coupled effects of activation energy and grain boundary energy. By application of the model to nanoscale grain growth of dense nanocrystalline gadolinia-doped ceria, a good agreement between the model predictions and the experimental results was obtained. It is shown that the interrelated effect of increased activation energy and decreased grain boundary energy induced thermal stability in the nanocrystalline materials.

The Mathematical Model and Emperiences Algorithm of Activation Energy of Mixed Wastes

Through the single center of gravity mixture experiment design, the thermogravimetric combustion experiments of the cotton, easy chopsticks, food bags and its mixed components were done. Then the combustion characteristics curves of thermogravimetric and thermogravimetric differntial, and each group point average activation energy were obtained by above experiments. Using three Scheffe polynomial and the average activation energy of each waste component combustion, we get the activation energy calculation empirical formula of mixed waste combustion empirical formula. Through the three vertices of gravity method mixed waste combustion test, the experimental results of mixed waste activation energy fit well with the activation energy calculated from empirical formula. The activation energy calculated from empirical formula is correct, therefore, can be used to calculate the empirical formula derived from mixed waste activation energy. Application of this method has important guiding significance to the design of waste incinerator actually works and the waste combustion adjust.

A thermokinetic description of nanoscale grain growth: Analysis of the activation energy effect

The inhibition of grain growth by solute segregation in nanoscale materials has often been described using kinetic models (e.g. Acta Mater 1999;47:2143) or thermokinetic models (e.g. Acta Mater 2009;57:1466), in which constant activation energy and a negligible effect of solute segregation on activation energy were assumed. In this paper, an intact thermokinetic model for nanoscale grain growth was developed by incorporating mixed effects of activation energy and grain boundary (GB) energy. By application of the model to nanoscale grain growth in Ni–P, Pb–Zr, Fe–Zr and Ru–Al alloys, the validity of the present model was confirmed, in combination with verification of the initial condition of GB segregation. On this basis, the increase of activation energy and the decrease of GB energy are interrelated and thus the kinetics and the thermodynamics of normal grain growth are linked. Based on a comparison of three characteristic velocities VTK, VGE and VAE of GB derived from the present thermokinetic model, grain boundary energy model and activation energy model, a mechanism of controlled nanoscale grain growth was proposed, which indicated a transition from a kinetic-controlled to a thermodynamic-controlled process.

Kinetics of Oxygen Diffusion into Multilayer Ceramic Capacitors during the Re-Oxidation Process and its Implications on Dielectric Properties

Re-oxidation is an important thermal process to minimize oxygen vacancies and produce high reliable Ni-MLCCs. The re-oxidation of these devices is then investigated with a series of “in-situ” impedance measurements between 400 and 500 °C in air. From the relative impedance change, chemical diffusion coefficients, associated activation energy and effective equivalent circuit model are determined. Those values were found to be reasonable compared with previous researchers’ data. Moreover, the proposed effective equivalent circuit model successfully represents the real Ni-MLCC morphology. From transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), it is found that the electrical properties and reliabilities of the Ni-MLCCs re-oxidized under different conditions are identical.

Evaluation of the activation energy of viscous flow for a binary mixture in order to estimate the thermodiffusion coefficient

The evaluation of the activation energy in Eyring's viscosity theory is of great importance in estimating the thermodiffusion coefficient for associating and non-associating fluid mixtures. Several methods were used to estimate the activation energies of pure components and then extended to mixtures of linear hydrocarbon chains. Results show that the recent model of Abbasi et al. [J. Chem. Phys. 131: 014502, 2009.] gives a good outcome in determining the activation energy of the components of a binary mixture. The activation energy model for pure components is shown to be useful for obtaining the activation energy of the mixture. In this paper, the activation energy model using alternative forms of Eyring's viscosity theory is used to estimate the thermodiffusion coefficient values for hydrocarbon binary mixtures. Comparisons of predicted thermodiffusion coefficients using different theoretical models with the experimental data show good capability of the activation energy model.

Device Modeling at Cryogenic Temperatures: Effects of Incomplete Ionization

We present a device performance modeling methodology that self-consistently resolves device operation at cryogenic temperatures (T > 30 K) in conjunction with incomplete ionization effects that take into account the change in dopant activation energies as a function of doping. Using this methodology, we developed a device simulator that predicts n-channel MOSFET (NMOSFET) device characteristics for a wide range of temperatures by solving semiconductor equations, along with the Poisson equation. Comparison of our calculated results with measurements shows that proper inclusion of variations in activation energy as a function of doping level is necessary for accurately monitoring device operation at cryogenic temperatures. Using dopant activation energies that are independent of doping levels leads to current rolloff and eventually device turn-off at low-temperature simulations. However, activation energy models that give lower activation energies for higher doping levels result in improved NMOSFET performance at colder temperatures, which agrees with experiments. Furthermore, calculations indicate that different incomplete ionization models affect the NMOSFET characteristics mainly through changes in the resistances of the heavily doped source and drain regions, and the substrate.