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•The optimum thickness of Sb2S3 is 350 nm and for Sb2Se3 is 760 nm.•The optimum metrics of tandem solar cell are: Jsc = 16.32 mA/cm2, Voc = 1.48 V, FF = 60.7 %, PCE = 14.66 %.•The ...optimum acceptor density and bulk defect density in Sb2S3 and Sb2Se3 are: NA = 8.9 × 1015 cm−3 and BDD = 7.21 × 10−15 cm−3.•The optimized radiative recombination rate in Sb2S3 and Sb2Se3 layers are 0.73 × 10−10 cm3/s and 6.5 × 10−11 cm3/s, respectively.
A device simulation presented for a tandem solar cell of Sb2S3 and Sb2Se3 as top (Eg = 1.7 eV) and bottom (Eg = 1.2 eV) absorber layers. We examined the device characteristics, radiative recombination, and optimum thickness of this tandem cell using filtered spectrum analysis and current-matching techniques in COMSOL. An open-circuit voltage of 1.58 V, current density of 15.50 mA/cm−2, fill factor of 56.90 %, and a remarkable efficiency of 14 %. The optimum thickness of Sb2S3 is 350 nm and for Sb2Se3 is 760 nm. Promising characteristics obtained with a Jsc = 16.32 mA/cm2, Voc = 1.48 V, FF = 60.7 %, and an overall power conversion efficiency of 14.66 %. The optimum acceptor and bulk defect density have been calculated to be NA = 8.9 × 1015 cm−3 and BDD = 7.21 × 10−15 cm−3. The optimized values of radiative recombination rate in Sb2S3 and Sb2Se3 are 0.73 × 10−10 cm3/s and 6.5 × 10−11 cm3/s, respectively.
Localized impedance measurements at the needle tip identifying the present tissue type could aid clinicians in needle procedures. To assess the sensitivity field of a hollow, bipolar needle ...electrode, a 3D finite element approach using COMSOL Multiphysics was chosen. The simulated bipolar needle electrode consists of two hypodermic needles (17 G and 23 G) with an insulating layer of polytetrafluoroethylene (PTFE) in between. Impedance values were recorded while steadily increasing the insertion depth of the needle electrode in a layered tissue structure of skin (dermis), fat, and blood. Simulation results reveal a highly local sensitivity volume around the needle tip that can be approximated by half a tri-axial ellipsoid with elliptic radii of 0.735 mm, 2.886 mm, and 1.774 mm. A comparison with simulated and measured impedance values shows great correspondence.
•A phase field model (PFM) for simulating complex crack patterns in rocks is presented.•The phase field model is implemented in COMSOL Multiphysics.•2D and 3D examples are presented.•The crack ...propagation, branching and coalescence in rock specimens are studied.
We present a phase field model (PFM) for simulating complex crack patterns including crack propagation, branching and coalescence in rock. The phase field model is implemented in COMSOL and is based on the strain decomposition for the elastic energy, which drives the evolution of the phase field. Then, numerical simulations of notched semi-circular bend (NSCB) tests and Brazil splitting tests are performed. Subsequently, crack propagation and coalescence in rock plates with multiple echelon flaws and twenty parallel flaws are studied. Finally, complex crack patterns are presented for a plate subjected to increasing internal pressure, the (3D) Pertersson beam and a 3D NSCB test. All results are in good agreement with previous experimental and numerical results.
A phase field model for fluid-driven dynamic crack propagation in poroelastic media is proposed. Therefore, classical Biot poroelasticity theory is applied in the porous medium while arbitrary crack ...growth is naturally captured by the phase field model. We also account for the transition of the fluid property from the intact medium to the fully broken one by employing indicator functions. We employ a staggered scheme and implement our approach into the software package COMSOL Multiphysics. Our approach is first verified through three classical benchmark problems which are compared to analytical solutions for dynamic consolidation and pressure distribution in a single crack and in a specimen with two sets of joints. Subsequently, we present several 2D and 3D examples of dynamic crack branching and their interaction with pre-existing natural fractures. All presented examples demonstrate the capability of the proposed approach of handling dynamic crack propagation, branching and coalescence of fluid-driven fracture.
•A phase-field modeling of dynamic fracture propagation in porous media is proposed.•The phase field method for dynamic cracks in a single-phasic solid is extended for fluid-driven dynamic cracks.•The crack propagation and branching is driven by elastic energy.•The presented results agree well with existing analytical results.•Examples of dynamic crack branching and its interaction with pre-existing natural fractures are presented.
Transport of multicomponent electrolyte solutions in saturated porous media is affected by the electrostatic interactions between charged species. Such Coulombic interactions couple the displacement ...of the different ions in the pore water and remarkably impact mass transfer not only under diffusion, but also under advection‐dominated flow regimes. To accurately describe charge effects in flow‐through systems, we propose a multidimensional modeling approach based on the Nernst‐Planck formulation of diffusive/dispersive fluxes. The approach is implemented with a COMSOL‐PhreeqcRM coupling allowing us to solve multicomponent ionic conservative and reactive transport problems, in domains with different dimensionality (1‐D, 2‐D, and 3‐D), and in homogeneous and heterogeneous media. The Nernst‐Planck‐based coupling has been benchmarked with analytical solutions, numerical simulations with another code, and high‐resolution experimental data sets. The latter include flow‐through experiments that have been carried out in this study to explore the effects of electrostatic interactions in fully three‐dimensional setups. The results of the simulations show excellent agreement for all the benchmarks problems, which were selected to illustrate the capabilities and the distinct features of the Nernst‐Planck‐based reactive transport code. The outcomes of this study illustrate the importance of Coulombic interactions during conservative and reactive transport of charged species in porous media and allow the quantification and visualization of the specific contributions to the diffusive/dispersive Nernst‐Planck fluxes, including the Fickian component, the term arising from the activity coefficient gradients, and the contribution due to electromigration.
Key Points
Nernst‐Planck‐based approach to model multidimensional transport, charge interactions, and chemical reactions in flow‐through porous media
Computation and visualization of diffusive/dispersive, electromigration, and activity coefficients' gradient fluxes
Code validated with high‐resolution 2‐D experimental data and first fully 3‐D data set on multicomponent ionic transport
A new mathematical model for spheroidal droplet heating and evaporation is proposed. This model takes into account the effect of liquid finite thermal conductivity and is based on the previously ...obtained analytical solution for the vapour mass fraction at the droplet surface and a new correlation for the convective heat transfer coefficient incorporated into the numerical code. The heat transfer equation in the liquid phase is solved numerically using the finite-element heat transfer module of COMSOL Multiphysics. It is shown that the lifetime of spheroidal (prolate and oblate) droplets is shorter than that of spherical droplets of the same volume. The difference in the lifetimes of spheroidal and spherical droplets, predicted by the new model, is shown to increase with increasing aspect ratios for prolate droplets and decreasing aspect ratios for oblate droplets. As in the case of stationary spherical droplets, the d2-law is shown to be valid for spheroidal droplets after the completion of the heat-up period. The predictions of this model agree with experimental observations. The duration of the heat-up period is shown to decrease with increasing aspect ratios for prolate droplets and decreasing aspect ratios for oblate droplets. The maximal surface temperatures are predicted near the regions where the surface curvature is maximal. The aspect ratios are shown to be weak functions of time, in agreement with experimental observations.
•A new mathematical model for spheroidal droplet heating and evaporation.•Effect of non-uniform surface temperature on droplet heating and evaporation.•The effect of liquid finite thermal conductivity is considered using COMSOL.•An analytical solution for the vapour mass fraction at the droplet surface is used.•A new correlation for the convective heat transfer coefficient is obtained and used.
•Based on the thermal damage concept generated during laser welding of biological tissues, we propose the degree of collagen denaturation and calculate it under progressively increasing dual-beam ...laser effective energy density.•The findings indicate that collagen denaturation did not exhibit a significant increase beyond an energy level of 115 J/mm2. By maintaining the energy density below 135.4 J/mm2 and the welding time at 300 s, precise control over the degree of collagen denaturation within the range of 0.00199–0.0235 is achievable.•By integrating GROMACS molecular dynamics simulations with an investigation of structural alterations in human type I collagen molecules during laser welding, our findings suggest that the optimal temperature threshold for skin wound laser welding is 55℃. When subjected to laser energy density conditions below 115 J/mm2, the thermal impact of the laser on skin tissue predominantly facilitates repair.•Utilizing the COMSOL Multiphysics Helmholtz Equation Module, finite element simulations were conducted to investigate alterations in the optical properties of skin during laser welding.•The findings suggest that at an energy level of 135.4 J/mm2, the photochemical effect assumes a more prominent role while inevitably resulting in a higher peak temperature of 70.4℃. By limiting the duration of laser welding to within 300 s, it becomes feasible to effectively regulate collagen denaturation within a reversible and reasonable range.
Based on the thermal damage concept, our work proposes the concept and calculation method of collagen denaturation degree. By integrating experimental calculations with GROMACS molecular dynamics simulation and finite element COMSOL numerical simulation of skin optical properties, we investigate the mechanisms underlying collagen fiber thermal denaturation and photochemical changes induced by laser irradiation. When the energy is below 115.68 J/mm2, the dominant factor in skin wound repair is the thermal energy delivered by the laser. The collagen denaturation degree can be maintained around 0.0199 during an effective laser welding time of 300 s, resulting in a peak temperature of approximately 55℃ and noticeable wrinkling and scattering of monomeric helical protein chains within the fiber structure. This wrinkled structure indicates macroscopic recombination and recoupling of fractured collagen fibers on both sides of the skin wound. However, when the laser energy density further increases to 135.4 J/mm2, there is only a slight increase in collagen denaturation degree without significant alterations observed. For this phenomenon, Finite element simulations based on Helmholtz equation modules reveal that reflectivity towards laser photons decreases significantly across tissue blocks due to enhanced photonics effects. As energy reaches or exceeds 135.4 J/mm2 levels, photothermal effects assume a more prominent role but inevitably lead to higher peak temperatures (70.4℃). Therefore, precise reduction in laser welding time within 300 s can effectively control collagen denaturation within reversible and reasonable ranges.
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•Energy conversion in a horn type sonicator was investigated under batch and continuous flow.•Acoustic power was varied depending on the liquid properties at a fixed nominal power of ...transducer.•A power relation was proposed for acoustic power prediction as a function of dimensionless groups.•Temperature, Pr and Oh numbers are the mains factors affecting acoustic to nominal power ratio.•Lower thermal energy conversion was obtained in continuous flow compared to batch configuration.
The level of knowledge on the non-thermal contribution of ultrasonic wave’s energy to perform physico-chemical phenomena is one of the bottlenecks for the commercialization purposes. Under constant nominal power of transducer (Pn), the input electrical power (Pin) is less and sensitive to the medium’s physical properties. This study attempts to assess the conversion of acoustic to thermal power experimentally and numerically using COMSOL Multiphysis@ for a 24 kHz horn-type sonicator through a medium without any sono-chemical effect. Single- and homogeneous two-phase Newtonian mixtures of sunflower oil and water (o/w) with a relatively wide range of density (914–998 kg/m3) and viscosity (0.5–63.5 mPa.s) were irradiated in a lab-scale vessel (1 L) under batch and continuous flow configuration. The direct influence of Pn (80–400 W) and o/w ratio (0–1) on temperature rise and subsequent thermo-physical properties of liquid and the indirect influence on Pin and thermal energy conversion (TEC) were investigated employing calorimetric method. A new engineering concept including a power factor correlation was proposed and validated for prediction of Pin as a function of liquid space velocity (ϑ), temperature, Prandtl (Pr) and Ohnesorge (Oh) dimensionless groups. The results showed that under constant temperature and Pn, increasing Pr and Oh increased Pin with a similar trend for both modes of operation. An increase in temperature directly led to a decrease in Pin with a power factor closed to “-1”. The Pin in continuous flow was higher compared to batch configuration at similar temperature, liquid properties, and Pn. This effect was more significant with increasing ϑ. An increase in ϑ at constant Pn led to a decrease in the inlet/outlet temperature difference in continuous flow and an increase in Pin. Increasing Pn resulted in higher TEC for both configurations; however, TEC was relatively lower in continuous flow than batch configuration indicating more efficient sonication in continuous flow.
•Multiphase flow and multicomponent reactive transport in coupled compartments•Impact of atmospheric forcing on gas component transport and geochemical reactions•COMSOL-PhreeqcRM coupling to simulate ...porous medium/free-flow systems•Key features of the coupled model illustrated with benchmark and application examples
The exchange of gas components across the subsurface/atmosphere interface influences multiphase flow and reactive transport in the subsurface and is crucial for many biogeochemical processes, for the emission of greenhouse gases, and for the fate of volatile contaminants. In this study, we present a modeling approach to simulate non-isothermal multiphase flow and multicomponent reactive transport in coupled subsurface/atmosphere compartments. The model is based on a coupled porous medium/free flow domain in which the Navier-Stokes equation is used to describe single-phase (gaseous) flow in the free-flow subdomain and Darcy's law is applied for two-phase flow in the porous medium subdomain (i.e., two-domain approach). The implementation is performed by coupling COMSOL Multiphysics and PhreeqcRM, which enables the investigation of the interplay between multi-physical processes (i.e., flow, mass and heat transport) in the coupled compartments and geochemical reactions in the porous medium. We first present a set of benchmark examples in which key features of the proposed model are tested against other numerical simulators and an analytical solution. Successively, we take advantage of the unique capabilities of the proposed approach to explore conservative and reactive transport of gas components in a coupled porous medium/free flow domain. The results show that the exchange processes between the compartments control the location of reactive zones and the extent of geochemical reactions (i.e., mineral dissolution) by changing the spatiotemporal distribution of fluid phases and enhancing the interphase mass transfer of key gas components such as oxygen and carbon dioxide.
We discuss the use of the commercial finite element software COMSOL Multiphysics® for electrochemical analysis. Practical considerations relevant to finite element modelling are highlighted. A review ...of contemporary applications of this software is supplied; the subjects concerned reveal the particular suitability of general-purpose finite element methods for non-standard geometries, complex reaction chemistry, hydrodynamic electrochemistry, and rapid verification of standard results.
•Account of built-in methods for electrochemistry in COMSOL Multiphysics.•Critical discussion of meshing finite element models for diffusion problems.•Review of publications using COMSOL Multiphysics in electroanalytical chemistry.
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