Laboratoř přenosu tepla a proudění

Browse

Now showing 1 - 5 of 57

Magnetohydrodynamics phenomena in continuous casting process under applied electromagnetic braking (EMBr)
(Elsevier B.V., 2025-06-22) Vakhrushev, Alexander; Karimi-Sibaki, Ebrahim; Wu, Menghuai; Al-Nasser, Mohamad; Hackl, Gernot; Tang, Yong; Watzinger, Josef; Boháček, Jan; Kharicha, Abdellah
n the presented work the effects of electromagnetic braking (EMBr) are gathered, exemplifying key magnetohydrodynamics (MHD) phenomena in continuous casting (CC) process. The complex interactions between turbulent liquid metal flows and a direct current (DC) magnetic field through the meso-to-macro scale cascade are reviewed. We analyze MHD influences on different types of melt motion in CC, including jets, recirculation zones, and shear flows, as well as Lorentz force-induced acceleration in stagnant regions. These phenomena result from the distribution of induced electric current lines closing through either the liquid bulk or the semiconducting solidifying shell. The continuously growing shell, formed against the water-cooled copper mold walls, is significantly affected by the hot melt flow patterns. The study highlights practical applications of EMBr to optimize flow dynamics in the CC process, providing insight into improving casting stability and product quality.
Modeling Heat Transfer in Cylindrical Batteries: Spiral-Based Thermal Conductivity Tensor
(Avestia Publishing, 2025-01-30) Hvožďa, Jiří; Boháček, Jan; Vakhrushev, Alexander; Karimi-Sibaki, Ebrahim
This study investigates the importance of considering the well-known spiral structure of cylindrical batteries in numerical models of heat transfer. Such models typically simplify the internal geometry by a concentric layout of electrodes and separators, resulting in an effective orthotropic thermal conductivity with radial, tangential, and axial components defined in a cylindrical coordinate system. However, the actual spiral structure suggests radius-dependent thermal conductivity. In this study, several thermal simulations were performed, comparing thermal fields obtained with the commonly used cylindrical orthotropy and a more realistic spiral structure. The results show that the spiral structure has a negligible effect on the overall temperature distribution for configurations with dense spirals and higher radial thermal conductivity (2 W·m1·K1). However, for lower radial thermal conductivity (0.2 W·m1·K1), considerable errors were observed even for dense spirals. These findings emphasize the need for studies to justify simplifications made in the thermal conductivity tensor.
A Coupled Magnetohydrodynamics (MHD) and Thermal Stress-Strain Model to Explore the Impact of Gas Cooling on Ingot Solidification Shrinkage in Vacuum Arc Remelting (VAR) Process
(Springer Nature, 2024-09-04) Boháček, Jan; Karimi-Sibaki, Ebrahim; Vakhrushev, Alexander; Mráz, Kryštof; Hvožďa, Jiří; Wu, Menghuai; Kharicha, Abdellah
An advanced 2D axisymmetric magnetohydrodynamics model, including calculations for electromagnetic, thermal, and flow fields, fully coupled with a thermal stress-strain model, allowing the computation of solid mechanical parameters like stress, strain, and deformation within the ingot of the vacuum arc remelting process is presented. This process encounters challenges due to solidification shrinkage, which causes losing contact between the ingot and the mold, reducing the cooling efficiency of the system, resulting in a deeper melt pool and decreasing ingot quality. Herein, the width of the air gap along the ingot, the precise position of contact between the ingot and mold, and the profile of the melt pool, affected by gas cooling, are calculated. The global pattern of transport phenomena, such as (electro-vortex) flow and electromagnetic fields in the bulk of the ingot, is insensitive to helium gas cooling through the shrinkage gap. However, including gas cooling significantly improves heat removal through the mold, which consequently reduces the pool depth of the Alloy 718 ingot, leading to an improvement in the quality of the ingot.
A numerical study on effects of current density distribution, turbulence, and magnetohydrodynamics (MHD) on electrolytic gas flow with application to alkaline water electrolysis (AWE)
(Elsevier, 2024-07-20) Karimi-Sibaki, Ebrahim; Vakhrushev, Alexander; Wu, Menghuai; Boháček, Jan; Kharicha, Abdellah
A three-phase Eulerian model is proposed to investigate the induced flow due to the generation of gas bubbles between two parallel plates without forced convection with application to alkaline water electrolysis (AWE). Earlier models, assuming a laminar regime, accurately predicted the multiphase flow near electrodes but struggled to calculate bulk liquid electrolyte flow away from them. Herein, we study the influences of electric current density distribution, turbulence effects, and the interaction between flow and the magnetic field known as magnetohydrodynamics (MHD). Based on our modeling results, the traditional method using an averaged uniform current density along electrodes (e.g. here 2000 A m 2) is feasible, as incorporating calculated nonuniform current distribution minimally affects the multiphase velocity field. The Lorentz force, originating from flow interaction with the (self-induced) magnetic field, is negligible compared to forces like drag or bubble dispersion. Consequently, MHD effects only become relevant upon introducing an external magnetic field. Including turbulence in the model, being minor in magnitude but non-negligible, significantly improves the predicted velocity profile. Modeling results are validated against an experiment.
A multiphase model for exploring electrochemical Marangoni flow
(Elsevier, 2023-10-01) Karimi-Sibaki, Ebrahim; Vakhrushev, Alexander; Kadylnykova, Anastasiia; Wu, Menghuai; Ludwig, Andreas; Boháček, Jan; Kharicha, Abdellah
A multiphase numerical model based on the volume of fluid (VOF) method is proposed to simulate the transient, electrochemically-generated Marangoni flow in a system comprising a NaOH electrolyte and a eutectic gallium–indium (EGaIn) metal droplet. The model incorporates appropriate equations to accurately represent the transport phenomena, including flow, electric potential, and electric current density, within the entire system. The model includes the transient variation in the interfacial tension as a function of electric current density at the interface, leading to the generation of Marangoni flow and enabling the tracking of droplet shape evolution. Notably, the model successfully captures the elongation of the droplet towards the cathode, which is validated through comparison with available experimental data.

Browse

Recent Submissions