Commercial Code COMSOL Multiphysics Research Articles

Three-dimensional analysis of multiple inclined borehole heat exchangers

This research develops and applies a numerical modelling method for inclined borehole heat exchangers (BHE) in ground-source heat pump systems. Inclined BHEs have the advantage of reducing the ground-level footprint of the overall BHE field. Computational modelling of the ground heat transfer using the commercial code COMSOL Multiphysics has revealed that inclined BHEs offer additional performance benefits compared to vertical BHE fields. When heat is injected constantly, both types of fields perform similarly at first, but over a longer period of time, the inclined BHE fields show significant benefits due to the increased ground volume in the deeper portion of the field. Similar conclusions are reached when transient loading conditions are considered. Notably, when cooling dominates, inclined BHE fields outperform vertical ones for a simulated period of 10 years. This indicates that inclined BHE fields are better equipped to handle imbalanced energy loads. To summarize, inclined BHE fields offer advantages in ground-volume utilization and resilience to energy load imbalances compared to vertical fields.

Water Movement Direction through an Anion Exchange Membrane Fuel Cell Exerted By Gas Humidity and Flow Rate: A Simulation Study

The growing demand for clean energy generation has been urged due to the threat of climate change by greenhouse emissions (1 kg of CO2 per 1 kW h of generated electricity). In 2021, the electricity generation rose to 1530 TW h, 62% coming from fossil fuels [1]. To lower this significant fossil fuels usage, the development and use of alternative energy sources and green fuels have reached a formidable level of interest. Renewable solar and wind energy sources are currently available; however, those appear to be limited by natural fluctuations in energy production relegated to day- and night-time wheatear or geographical regions [2]. Electrochemical energy storage and conversion technologies can be employed to minimize production variations as an alternative to this limitation. The anion-exchange membrane fuel cell (AEMFC) is an excellent alternative for energy generation due to its air CO2-free emissions, low-cost electrocatalyst used at the cathode, and industrial-scale membrane production [3]. The design of a fuel cell involves several tightly interrelated factors, such as electrode and membrane materials, reactor geometry, and characterization of the reaction environment in terms of the momentum, mass and heat transport, electrode kinetics, and current distribution, to find the best operational conditions to reach a suitable energy efficiency [4]. In either case, the present work deals with designing a hybrid flow-field single-fuel cell. The monopolar anode plate is a multiple-serpentine flow field that benefits the water drainage. On the other hand, the cathode plate is an interdigitated leaf-type flow field that might ensure an efficient gas reactant distribution over the entire electrode geometric area.A two-phase flow CFD simulation is performed to analyze the influence of the flow field patterns on the mass transport processes in the electrodes. Moreover, the water movement direction through the membrane as a function of the operational conditions is presented. The commercial code COMSOL Multiphysics was used to solve the transport equations through the finite element method.In the experimental field, the water movement direction between the anodic and cathodic sides shows the capability to favor the electro-osmotic drag (EOD) or the diffusion water transport mechanism under different gas flow rates and humidities, as shown in Figure 1a. Accordingly, the results demonstrated that the EOD predominance was promoted when low symmetric flow rates (125 cm3 min-1 for anode and cathode) were used in the AEMFC. On the contrary, the water diffusion dominance appears under asymmetric flow rates between anode and cathode (125 and 250 cm3 min-1, respectively). The different tested relative humidities do not influence the water direction once the flow rates are given. The AEMFC performance was affected by the water transport mechanism, giving lower peak power densities for EOD-dominated systems (35.2 mW cm-2, in Figure 1b) than those obtained by diffusion (62.8 mW cm-2, in Figure 1c). The most suitable operating condition is for water diffusion dominance at non-saturated streams, where a decrease in performance is experienced as the flow becomes saturated (at higher humidifier temperature). A close agreement between simulation and experimental results was obtained regarding current-potential curves and water movement through the membrane dictated by electro-osmotic drag and water diffusion.

Numerical Investigation of a Thermal Ablation Porous Media-Based Model for Tumoral Tissue with Variable Porosity

Thermal ablation is a minimally or noninvasive cancer therapy technique that involves fewer complications, shorter hospital stays, and fewer costs. In this paper, a thermal-ablation bioheat model for cancer treatment is numerically investigated, using a porous media-based model. The main objective is to evaluate the effects of a variable blood volume fraction in the tumoral tissue (i.e., the porosity), in order to develop a more realistic model. A modified local thermal nonequilibrium model (LTNE) is implemented including the water content vaporization in the two phases separately and introducing the variable porosity in the domain, described by a quadratic function changing from the core to the rim of the tumoral sphere. The equations are numerically solved employing the finite-element commercial code COMSOL Multiphysics. Results are compared with the results obtained employing two uniform porosity values (ε = 0.07 and ε = 0.23) in terms of coagulation zones at the end of the heating period, maximum temperatures reached in the domain, and temperature fields and they are presented for different blood vessels. The outcomes highlight how important is to predict coagulation zones achieved in thermal ablation accurately. In this way, indeed, incomplete ablation, tumor recurrence, or healthy tissue necrosis can be avoided, and medical protocols and devices can be improved.

Study of the usability of sinusoidal function heat flux based on enthalpy-porosity technique for PCM-related applications

The present study summarizes a two-dimensional (2D) numerical simulation of a phase change material (PCM) melting/solidification processes in a square cavity. The objectives of this study are to study and compare the effect of the application of different applied thermal boundary conditions such as constant or variable thermal flux during the melting and solidification processes of a PCM. Here, the convective heat transfer is taken into account according to the Boussinesq approximation. The commercial code COMSOL Multiphysics is used, and the “Voller model” based on the enthalpy-porosity technique is applied on a fixed computational grid. Results presented in terms of solid–liquid fraction, flow structure, isotherms, and stored and released thermal energy have shown that the melting time for the applied variable heat flux is reduced compared to that of constant heat applied flux. In addition, it was found that the PCM melting time was shorter than the solidification time. Therefore, the use of variable (sinusoidal) heat flux conditions can be useful in engineering applications such as thermal energy storage applications (PCM life cycle test, solar energy where a variable heat flow is involved due to the change of day).

Thermo-Fluid-Dynamics of a Ceramic Foam Solar Receiver: A Parametric Analysis

The high efficiency of concentrated solar power (CSP) in energy conversion makes it a very attractive device for using solar energy as a substitute of nonrenewable energy sources. The open volumetric receiver plays an important role in the performance of a CSP. The optimized design of solar receiver implies the thorough knowledge of the heat transfer between the air and the foam and of the temperature distribution in the receiver. Heat transfer in the cylindrical SiC porous volumetric receiver of a solar tower, undergoing the impact of concentrated solar radiation, is investigated numerically in this paper. Governing equations are written with the volume averaging technique. A two-equation model for the energy equation, under the local thermal nonequilibrium assumption, is used. Numerical simulations are carried out through the commercial code COMSOL Multiphysics. The solid and fluid temperatures, the fluid velocity and the pressure drop, for various boundary and morphological conditions, are predicted and discussed. The receiver efficiency is finally maximized carrying out an extended parametric analysis of process parameters.

Thermal building control using active ventilated block integrating phase change material

In the context of improving energy efficiency and thermal comfort in the building, the use of phase change materials (PCMs) is one of the suggested solutions. The proposed integration solutions concern the building envelope as well as the applications related to its operation. The study of the incorporation of PCM in the walls of the building was the subject of numerous works. However, the antisymmetric character of storing/recovering energy management in the walls is less controlled and do not fit the optimal conditions. In this study, a solution based on the direct integration of a stabilized PCM (gel) in an envelope including ventilation channels, was proposed to overcome this problem of antisymmetry storing/recovering and fitting with different fixed ambient conditions. The final aim is to develop the optimization strategy of a wall combining the heavy inertia offered by the PCM, intra-ventilation control and the contribution to air renewal energy demand.In this context, an experimental study of a concrete block system is conducted to test the thermal response of this configuration by the application of cyclic solicitations. The comprehension of this integrated constructive solution essentially passes by the possession of validated numerical tools. For this, two models have been developed. The first model using the electrical–thermal analogy, based on an RC equivalence, is distinguished by its relative simplicity and weak time computing demand. Each of these two factors, R and C summarise the system properties and has a direct influence on the building transient simulations over a year. The second one is based on direct numerical simulation DNS of the energy and fluid flow equations using commercial code COMSOL Multiphysics. Such DNS is time consuming and could not be used to simulate over a year but aims only to validate the first RC circuit approach. A comparison of these two models with the idealised experimental data was carried out and allowed the validation of the thermal behaviour of the solution based on the integration of the PCM with core ventilation.

Modeling of the densification of silver particles during sintering at controlled pressure and temperature

The control of the densification of a powder compact during the sintering process is of primary interest since this affects directly the obtained mechanical and physical properties. For example, silver sintering can be used to obtain joints for assembling optical or electronic components and, in such applications, an efficient thermal conductivity and a good material strength are requested. These properties are shown to be dependent on the density reached during compaction [1]. In our study, a well-established analytical model [2] is first employed to predict the main characteristics of the sintered material, such as the neck growth and the shrinkage during the initial stage of sintering. Effects of the temperature and the applied pressure are accounted for in the calculations, showing the ability of the model to find the optimal process parameters for some given objectives. The results are complemented with the densification estimation at the final stage of sintering obtained from a finite element simulation. The constitutive laws, which are implemented in the commercial code COMSOL Multiphysics, are based on a continuum approach of the sintered material as developed in [3,4].

Numerical Study of Convection and Radiation Heat Transfer in Pipe Cable

Pipe cable is considered as an important form for underground transmission line. The maximum electrical current (ampacity) of power cable system mostly depends on the cable conductor temperature. Therefore, accurate calculation of temperature distribution in the power cable system is quite important to extract the cable ampacity. In the present paper, the fluid flow and heat transfer characteristics in the pipe cable with alternating current were numerically studied by using commercial code COMSOL MULTIPHYSICS based on finite element method (FEM). The cable core loss and eddy current loss in the cable were coupled for the heat transfer simulation, and the difference of heat transfer performances with pure natural convection model and radiation-convection model was compared and analysed in detail. Meanwhile, for the radiation-convection model, the effects caused by radiant emissivity of cable surface and pipe inner surface, as well as the cable location in the pipe, were also discussed. Firstly, it is revealed that the radiation and natural convection heat flux on the cable surface would be of the same order of magnitude, and the radiation heat transfer on the cable surface should not be ignored. Otherwise, the cable ampacity would be underestimated. Secondly, it is found that the overall heat transfer rate on the cable surface increases as the cable surface emissivity increases, and this is more remarkable to the upper cable. While the effect caused by the radiant emissivity on the pipe inner surface would be relatively small. Furthermore, it is demonstrated that, as cable location in the pipe falls, the natural convection heat transfer would be enhanced. These results would be meaningful for the ampacity prediction and optimum design for the pipe cable.

A model of water-spray cooling effect on a continuous casting process

The intention of this study is to give an idea about the influence of water-spray cooling on the solidification process of the liquid metal which enables to locate the shear region. The effect of spray heat transfer coefficient (hspray) during the liquid-to-solid transition through the cooled zone temperature and the metal latent heat of solidification are highlighted. A gray iron continuous casting process subjected to water-sprays cooling was simulated using the commercial code COMSOL MULTIPHYSICS 5.2. The obtained results show the great influence of hspray on the location of transition region as well as the relationship between hspray, wall outer temperature, latent heat dissipation, and the solidification time.

Numerical and experimental study of a SHM system for a drop-ply delaminated configuration

The present paper presents the experimental and FE numerical analyses of a Structural Health Monitoring system for a drop-ply configuration. In order to verify the mechanical experimental setup of the assembling between the host structure and the piezo-film patches in term of constraint, transient and modal analyses are first performed in order to compare the experimental responses to those obtained by from the numerical analyses performed with the commercial code COMSOL Multiphysics®. Then the Finite Element modelling of the piezoelectric sensors, to be used in the numerical analysis of the assembled structure, is validated through the comparison with the experimental data provided by the sensors manufacturer. Lastly, dynamic experimental and numerical analyses are performed on the undamaged and damaged drop-ply configuration in order to verify the effectiveness of a damage index in highlighting the position of the delamination tips.

Bayes approach to solving T.E.A.M. benchmark problems 22 and 25 and its comparison with other optimization techniques

The Bayes approach is used for solution of benchmark problems 22 and 25. The main purpose of the paper is to evaluate its applicability for solving complex technical problems (up to now, this technique was only very rarely used in the domain of such tasks). The parameters of this approach are compared with characteristics of several other heuristic and deterministic optimization techniques implemented in commercial code COMSOL Multiphysics and own open-source application Agros Suite. The results confirm that the Bayes approach is superior in a number of aspects and for the solution of real-life tasks it represents a powerful and prospective alternative to existing optimization methods

Numerical simulation of thermally induced residual stresses in friction stir welding of aluminum alloy 2024-T3 at different welding speeds

The paper deals with a numerical finite element simulation of the residual stress evolution in friction stir welding of 6 mm thick aluminum alloy AA2024-T3. The transient thermal field during the welding process was calculated with the commercial code COMSOL Multiphysics 5.0. Therefore, a thermal-pseudo-mechanical (TPM) heat source was implemented. A subsequent mechanical simulation was performed with varying hardening models for different welding speeds of 60 and 300 mm/min. The influence of softening of the material, which was due to hardening precipitation dissolution associated to the heating, was also investigated. Experiments in terms of thermocouple measurements as well as Vickers hardness and X-ray measurements of the residual stresses were conducted and compared to numerically obtained results. A qualitatively as well as quantitatively good agreement was found for different applied welding speeds.

Measurement of electromagnetic pulses generated during interactions of high power lasers with solid targets

A target irradiated with a high power laser pulse, blows off a large amount of charge and as a consequence the target itself becomes a generator of electromagnetic pulses (EMP) owing to high return current flowing to the ground through the target holder. The first measurement of the magnetic field induced by the neutralizing current reaching a value of a few kA was performed with the use of an inductive target probe at the PALS Laser Facility (Cikhardt et al. Rev. Sci. Instrum. 85 (2014) 103507). A full description of EMP generation should contain information on the spatial distribution and temporal variation of the electromagnetic field inside and outside of the interaction chamber. For this reason, we consider the interaction chamber as a resonant cavity in which different modes of EMP oscillate for hundreds of nanoseconds, until the EMP is transmitted outside through the glass windows and EM waves are attenuated. Since the experimental determination of the electromagnetic field distribution is limited by the number of employed antennas, a mapping of the electromagnetic field has to be integrated with numerical simulations. Thus, this work reports on a detailed numerical mapping of the electromagnetic field inside the interaction chamber at the PALS Laser Facility (covering a frequency spectrum from 100 MHz to 3 GHz) using the commercial code COMSOL Multiphysics 5.2. Moreover we carried out a comparison of the EMP generated in the parallelepiped-like interaction chamber used in the Vulcan Petawatt Laser Facility at the Rutherford Appleton Laboratory, against that produced in the spherical interaction chamber of PALS.

Modeling and analysis of hydraulic dashpot for impact free operation in a shut-off rod drive mechanism

Rotary hydraulic dashpot used for shut-off rod drive mechanism application of a nuclear reactor has been studied in this paper for impact free operation. The rotary hydraulic dashpot has been modeled as a system with 1 degree of freedom (DOF) and the simulation results are experimentally validated. The dashpot is modeled as a hinge joint with moving and fixed vanes as rigid bodies. Shut-off rods are used to shut-down a nuclear reactor and hydraulic dashpot absorbs the energy of freely falling shut-off rod at the end of rod travel. With the increase in the environmental temperature the dashpot becomes underdamped at a point because of reduction in the viscosity of oil and results into impact on mechanism components. Hydraulic dashpot designs are finalized with an optimum combination of dashpot clearances and oil viscosity to meet the drop time criterion and impact free operation at room temperature as well as at elevated temperature. Also with the change in mechanical loads the dashpot becomes underdamped. So the study is further extended to see the effects of various parameters such as moment of inertia, constraint angle and applied moment on the dashpot. Study is focused on obtaining dashpot responses in terms of relative rotation, relative angular velocity and relative angular acceleration at various environmental temperatures. Finite element commercial code COMSOL Multiphysics 5.1 has been used for numerical simulations. Equations for both rigid body dynamics and heat transfer in solids are solved simultaneously. Thus, energy absorbed and local temperature rise in the dashpot operation is also obtained. Both simulation and experimental results at wide range of environmental temperature are presented and compared in this paper. This study forms a good tool to design a hydraulic dashpot, which gives impact free operation in a shut-off rod free fall.

Passive temperature compensation in hydraulic dashpot used for the shut-off rod drive mechanism of a nuclear reactor

Passive temperature compensating hydraulic dashpot has been studied numerically as well as experimentally in this paper. Study is focused on reducing the clearances of the hydraulic dashpot at elevated temperature which intern compensates for the reduction in viscosity of damping oil and the dashpot gives uniform performance for wide range of temperature variation. Temperature compensation effects are mainly due to difference in the thermal expansion of materials. Different combinations of materials are used to reduce the dashpot clearances at elevated temperature. Finite element commercial code COMSOL Multiphysics 5.1 has been used for numerical analysis. Fluid-structure analysis has been carried-out to study the thermal expansion and pressure generated in the hydraulic dashpot. Multiphysics study with solid mechanics, laminar flow and moving mesh interfaces has been carried-out. Thermal expansion results of study-1 (solid mechanics) are further extended in to study-2 (laminar flow and moving mesh) and dashpot pressure is estimated. These results show that bimetallic strip improves the dashpot performance at 55°C but do not fully compensate beyond that and less severe impacts occurs. Specific combinations of design and materials have been presented in this paper for obtaining maximum temperature compensation. A novel passive temperature compensating hydraulic dashpot design has been presented, which is suggested for use over wide range of temperature change without much variation in the damping performance.

Numerical and experimental study of hydraulic dashpot used in the shut-off rod drive mechanism of a nuclear reactor

Hydraulic dashpot design for shut-off rod drive mechanism application in a nuclear reactor has been analyzed both numerically and experimentally in this paper. Finite element commercial code COMSOL Multiphysics 4.3 has been used for numerical analysis. Experimental validation has been done at two different cases. Experimental test set-ups and hydraulic dashpot constructions have been described in detail. Various combinations of dashpot oil viscosity and clearance thickness have been analyzed. Important experimental results are also presented and discussed. Pressure distributions in the dashpot chambers obtained from COMSOL are given for both the set-ups. Numerical and experimental results are compared. Dashpot designs have been qualified after detailed analysis and testing on full-scale test stations simulating actual reactor conditions (except radiation).

3D Numerical Simulation of Heat Transfer of a Heated Plate under the Electric Field Generated by a Needle Electrode

A three-dimensional numerical model that couples the electric field, velocity field, and temperature field is developed based on the commercial code COMSOL Multiphysics. The influences of several factors on convective heat transfer on a heated plate in the electric field generated by a needle electrode are observed. The factors are the applied voltage, the distance between the two electrodes, and the size of the ground plate. The results show that applied voltage is one of the most important factors for the convection heat transfer. The convection heat transfer efficiency significantly increases with the improvement of the applied voltage. From the perspective of the model size, the decrease of the distance between two electrodes and the size of the plate could improve the average convection heat transfer coefficient. Smaller ionic wind device needs lower applied voltage and less electric energy to obtain the same average convection heat transfer coefficient as the bigger one, which provides the theoretical basis for the potential of miniaturizing the ionic wind cooling device.

Slotted Blades Savonius Wind Turbine Analysis by CFD

In this paper a new bucket configuration for a Savonius wind generator is proposed. Numerical analyses are performed to estimate the performances of the proposed configuration by means of the commercial code COMSOL Multiphysics® with respect to Savonius wind turbine with overlap only. Parametric analyses are performed, for a fixed overlap ratio, by varying the slot position; the results show that for slot positioned near the blade root, the Savonius rotor improves performances at low tip speed ratio, evidencing a better starting torque. This circumstance is confirmed by static analyses performed on the slotted blades in order to investigate the starting characteristic of the proposed Savonius wind generator configuration.

A new approach to compute multi-reflections of laser beam in a keyhole for heat transfer and fluid flow modelling in laser welding

It is widely accepted that laser reflections can play a critical role during keyhole laser welding. The energy concentration, the mask effects and the laser polarization can directly affect the molten pool dynamic. In this paper a new approach to compute laser reflections is proposed which consists of treating laser under its wave form by solving Maxwell's equations. The method has the advantage to be easily coupled with heat transfer and fluid flow equations and can be immediately transposable in any 2D, 2D axi or 3D configurations. The reliability and limits of this approach are discussed through different numerical examples. The complete model takes into account the three phases of the matter: the vaporized metal, the liquid phase and the solid base. To predict the evolution of these three phases, coupled equations of energy, continuity, momentum and Maxwell are solved. The liquid/vapour interface is tracked using the level-set method. All these physics are solved simultaneously with the commercial code COMSOL Multiphysics®. The calculated temperatures, velocities and free surface deformation are analysed. Examples of simulations leading to the formation of porosity are also presented. Finally, melt pool shapes evolution are compared to experimental macrographs.

A model comparison to predict heat transfer during spot GTA welding

The present work deals with the estimation of the time evolution of the weld fusion boundary. This moving boundary is the result of a spot GTA welding process on a 316L stainless steel disk. The estimation is based on the iterative regularization method. Indeed, the three problems: direct, in variation and adjoint, classically associated with this method, are solved by the finite element method in a two-dimensional axisymmetric domain. The originality of this work is to treat an experimental estimation of a front motion using a model with a geometry including only the solid phase. In this model, the evolution of this solid domain during the fusion is set with the ALE moving mesh method (Arbitrary Lagrangian Eulerian). The numerical developments are realized with the commercial code Comsol Multiphysics® coupled with the software Matlab®. The estimation method has been validated in a previous work using theoretical data ([1]). The experimental data, used here for this identification are, temperatures measured by thermocouples in the solid phase, the temporal evolution of the melt pool boundary observed at the surface by a fast camera and the maximal dimensions of the melted zone measured on macrographs. These experimental data are also compared with numerical results obtained from a heat and fluid flow model taking into account surface tension effects, Lorentz forces and the deformation of the melt pool surface under arc pressure.