A 2-D axisymmetric fluid model simulation of inductively coupled discharges of a methane plasma is presented. The continuity equations for charged species and electron energy are solved with COMSOL ...Multiphysics. A constant frequency and gas pressure, 13.56 MHz and 0.02 Torr, respectively, are used. Initially, a coil power of 100 W is used, but this is later adjusted to include various coil powers up to 600 W. A Boltzmann equation solver is used to calculate the electron energy distribution function (EEDF) and reduced electron mobility. The effects of increased coil power are investigated, and the results indicate that increases in power increases moderately the electron temperature and charge densities. The growth rate of carbon across the substrate holder is mapped to determine a growth profile for the system.
In this letter, a design technique is presented to reduce the cross-axis sensitivity (CAS) in single-drive multi-axis microelectromechanical systems (MEMS) gyroscope. A design technique based on ...resonant mode ordering concerning drive-displacement amplitudes ratio and frequency differences ratio was proposed. A simplified single-drive multi-axis MEMS gyroscope, based on the mode-split approach, was analyzed for cross-axis sensitivity. The designed gyroscope utilizing a driving scheme based on a simple folded coupling spring has equal x and y – axes drive-displacement amplitudes of 3.892 μm respectively. The proposed resonant mode ordering technique was used, and an equal sense-frequency difference of 184 Hz was achieved with respect to drive-mode frequency. The designed gyroscope having common resonant mode order was analyzed, and CAS of x and y – axes was computed to be 0.241% and 0.387% respectively. The proposed resonant mode order technique successfully reduced the cross-axis sensitivity in the designed gyroscope. The reduced cross-axis sensitivities of x and y – axes were 0.025% and 0.076% respectively. Comparison of both designs showed a reduced rate of 89.627% and 80.362% in x and y – axes respectively. The main sensitivities of x and y – axes were computed to be 0.055 nm/dps respectively. Furthermore, the significance of the proposed technique was experimentally verified.
Display omitted
•A design technique was presented to reduce cross-axis sensitivity in single-drive, multi-axis MEMS gyroscope.•Resonant mode order concerning drive-displacement amplitudes ratio and sense frequency differences ratio was proposed.•Cross-axis sensitivity was successfully reduced, showed a reduced rate of 89.627% and 80.362% in x and y – axes respectively.•Furthermore, the significance of the proposed technique was experimentally verified.
In this work, thermal processes occurring in the sputtering unit of a DC magnetron with a hot titanium target are studied. The processes are described within the framework of a stationary heat ...problem with a surface source using a three-dimensional homogeneous Fourier equation. The problem was solved numerically using the Heat Transfer Module of the COMSOL Multiphysics software. The novelty of the work is the creation of a 3D model of a vacuum chamber with a sputtering unit attached to it. In this case, in the boundary conditions, the heat removal from the target of the sputtering unit is specified, not only in the form of radiation and by the elements of the target attachment, but also due to the thermal conductivity of the gas. The effective temperature of the target surface is revealed to be dependent on the discharge current and pressure exponentially. The simulation results conform with the experimental data.
•A magnetron equipped with a sputtering unit with a hot target was studied.•Thermal processes on the target were simulated by the COMSOL Multiphysics software.•Hot target effective temperature drops exponentially when argon pressure increases.•Simulation results conform with the experimental data.
A highly sensitive quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor based on a custom quartz tuning fork (QTF) with a small-gap of 200 μm was demonstrated. With the help of the finite ...element modeling (FEM) simulation software COMSOL, the change tendency of the QEPAS signal under the influence of the laser beam vertical position and the length of the micro-resonator (mR) were calculated theoretically. Water vapor (H₂O) was selected as the target analyte. The experimental results agreed well with those of the simulation, which verified the correctness of the theoretical model. An 11-fold signal enhancement was achieved with the addition of an mR with an optimal length of 5 mm in comparison to the bare QTF. Finally, the H₂O-QEPAS sensor, which was based on a small-gap QTF, achieved a minimum detection limit (MDL) of 1.3 ppm, indicating an improvement of the sensor performance when compared to the standard QTF that has a gap of 300 μm.
The heat dissipation has been rarely investigated in solar cells although it has a significant impact on their performance and reliability. For the first time, an extended three-dimensional (3-D) ...simulation of heat distribution in perovskite solar cells is presented here. We use COMSOL Multiphysics to investigate the temperature distribution in conventional perovskite solar cells through a coupled optical-electrical-thermal modules. Wave optics module, semiconductor module, and heat transfer in solid module are coupled in COMSOL Multiphysics package to perform the simulation in 3-D wizard. The electrical behavior, optical absorption, and heat conduction or convection are considered to gain insight into heat dissipation across the cell. The simulation results suggest that the heat produced in the cell is best dissipated from the metallic contact where the PbI2 defect forms because of oxidation or decomposition of the perovskite layer at moisture exposure. The generated heat varies significantly from the front FTO contact to bottom metallic electrode. The more heat dissipation and accumulation is observed at the junction and electrode sides too. In our simulations, we consider the Joule heating, nonradiative recombination heating, and heat flux in every layer of the cell and calculate the carrier's concentration, electric field distribution, Joule heating, Shockley-Read-Hall heating, total heat flux, and temperature distribution across the solar cell structure. The simulations reveal that the metallic contact must be selected as a highly heat conductive material in order to accelerate the heat dissipation on the bottom of the cell and to enhance the cell reliability against temperature increase under normal operation.
A numerical 3D model of coupled transport phenomena and texture changes during the roasting of chicken breast meat in a convection oven was developed. The model is based on heat and mass transfer ...coupled with the kinetics of temperature induced texture changes of chicken breast meat. The partial differential equations of heat and mass transfer as well as the ordinary differential equations that describe the kinetics of the texture changes were solved using COMSOL Multiphysics® 5.2a. The predicted temperature, moisture and texture (hardness, chewiness and gumminess) profiles were validated using experimentally values. The developed model enables the prediction of the texture development inside the chicken meat as function of the process parameters. The model predictions and measured values show the clear effect of changing process settings on the texture profiles during the roasting process. Overall, the developed model provides deep insights into the local and spatial texture changes of chicken breast meat during the roasting process that cannot be gained by experimentation alone.
•A mechanistic 3D model for the roasting of chicken breast meat was developed.•Temperature and moisture profiles were predicted.•The heat and mass transfer was coupled with the kinetics of texture changes.•This enabled the prediction of the spatial texture changes during the roasting process.•A good agreement between model predictions and experimental values was found.
Application of nanosecond pulsed electric fields to insulating nanoparticles can be used to prepare oriented high-performance composites, but the mechanism and related laws are still unclear. ...Therefore, in this article, highly insulating boron nitride nanosheet (BNNS) nanoparticles are selected, their alignment motions under different nanosecond intraburst frequencies (100 Hz-1 MHz) are studied for the first time in both experiments and simulations, and the two sets of results are compared and analyzed. The results show that the simulation results based on COMSOL are in good agreement with the experimental results, the variations in the local orientation angle with time and the local orientation time with intraburst frequency can be expressed by an allometric function, and the variation in the center-to-center distance with time can be described by an exponential decay function. Further experiments show that with the continuous application of the pulsed electric field, short chains of BNNSs continue to move to form longer chains, and long chains of 342 <inline-formula> <tex-math notation="LaTeX">\mu </tex-math> </inline-formula>m form under the external application of the pulsed electric field for 3 min. The good agreement between experiments and simulations verifies the strong reliability of the proposed theory and the established mathematical model for predicting the orientation alignment motion of BNNS particles. The theory and simulation method can be used as effective tools to predict the trajectories of nanoparticles under a nanosecond pulsed electric field and their final alignment into chains.
•Effects of viscous dissipation on thermo-viscous fingering instability are studied.•The finite element method is used to model the viscous fingering in porous media.•An Arrhenius equation of state ...is considered for viscosity of both phases.•It is found that increasing the viscous dissipation stabilizes the flow field.•The effects of Lewis number and thermal lag coefficient are studied in detail.
The thermo-viscous fingering instability associated with miscible displacement through a porous medium is studied numerically, motivated by applications in upstream oil industries especially enhanced oil recovery (EOR) via wells using hot water flooding and steam flooding. The main innovative aspect of this study is the inclusion of the effects of viscous dissipation on thermal viscous fingering instability. An Arrhenius equation of state is employed for describing the dependency of viscosity on temperature. The normalized conservation equations are solved with the finite element computational fluid dynamics code, COMSOL (Version 5) in which glycerol is considered as the solute and water as the solvent and the two-phase Darcy model employed (which couples the study Darcy flow equation with the time-dependent convection-diffusion equation for the concentration). The progress of finger patterns is studied using concentration and temperature contours, transversely averaged profiles, mixing length and sweep efficiency. The sweep efficiency is a property widely used in industry to characterize how effective is displacement and it can be defined as the ratio of the volume of displaced fluid to the total volume of available fluid in a porous media in the displacement process. The effects of Lewis number, Brinkman number and thermal lag coefficient on this instability are examined in detail. The results indicate that increasing viscous dissipation generates significant enhancement in the temperature and a marked reduction in viscosity especially in the displaced fluid (high viscous phase). Therefore, the mobility ratio is reduced, and the flow becomes more stable in the presence of viscous dissipation.
PDF
