Mainul Hasan

Coupled turbulent flow, heat, and solute transport in continuous casting processes

A fully coupled fluid flow, heat, and solute transport model was developed to analyze turbulent flow, solidification, and evolution of macrosegregation in a continuous billet caster. Transport equations of total mass, momentum, energy, and species for a binary iron-carbon alloy system were solved using a continuum model, wherein the equations are valid for the solid, liquid, and mushy zones in the casting. A modified version of the low-Reynolds numberk-ε model was adopted to incorporate turbulence effects on transport processes in the system. A control-volume-based finite-difference procedure was employed to solve the conservation equations associated with appropriate boundary conditions. Because of high nonlinearity in the system of equations, a number of techniques were used to accelerate the convergence process. The effects of the parameters such as casting speed, steel grade, nozzle configuration on flow pattern, solidification profile, and carbon segregation were investigated. From the computed flow pattern, the trajectory of inclusion particles, as well as the density distribution of the particles, was calculated. Some of the computed results were compared with available experimental measurements, and reasonable agreements were obtained.

Modelling of a single confined turbulent slot jet impingement using various k — ϵ turbulence models

Abstract Results of numerical simulation of two-dimensional flow field and heat transfer impingement due to a turbulent single heated slot jet discharging normally into a confined channel are presented. Both low-Reynolds and high-Reynolds number versions of k — ϵ turbulence models were used to model the turbulent jet flow. A control-volume-based finite-difference method was used to solve the governing mass, momentum, turbulent kinetic energy, turbulent kinetic energy dissipation rate, and energy equations iteratively. The parameters studied were the jet Reynolds number (5000

NUMERICAL STUDY OF COUPLED TURBULENT FLOW AND SOLIDIFICATION FOR STEEL SLAB CASTERS

A two-dimensional numerical modeling study was undertaken to account for coupled turbulent flow and heat transfer with solidification in the mold and submold regions of a steel slab coaster. Liquid steel is introduced into a water-cooled mold through a bifurcated submerged entry nozzle. Turbulence phenomena in the melt pool of the caster were accounted for, using a modified version of the low-Reynolds-number {kappa}-{epsilon} turbulence model of Launder and Sharma. The mushy region solidification, in the presence of turbulence, was taken into account by modifying the standard enthalpy-porosity technique, which is presently popular for modeling solidification problems. Thermocapillary and buoyancy effects have been considered in this model to evaluate the influences of the liquid surface tension gradient at the meniscus surface, and natural convection on flow patterns in the liquid pool. Parametric studies were carried out to evaluate the effects of typical variables, such as inlet superheat and casting speed, on the fluid flow and heat transfer results. The numerical predictions were compared with available experimental data.

Laminar flow and heat tranfer from multiple impinging slot jets with an inclined confinement surface

Abstract Results of numerical simulation of two-dimensional flow field and heat transfer due to laminar heated multiple slot jets discharging normally into a converging confined channel are presented. A control volume-based finite difference method was employed to solve the governing mass, momentum and energy equations. To handle the complexity of the geometry a program was developed using a non-orthogonal body-fitted coordinate system. A fully staggered grid system was generated using the solution to a set of elliptic grid generation equations. The parameters studied were: the jet Reynolds number (600

Numerical simulation of turbulent flow and heat transfer in the wedge-shaped liquid metal pool of a twin-roll caster

Abstract Controlled flow and heat transfer are important for the quality of a strip in a twin-roll continuous casting process. A numerical study was carried out to investigate the two-dimensional turbulent flow and heat transfer in the liquid stainless-steet-filted wedge-shaped cavity formed by the two counterrotating roils in a twin-roll continuous casting system. The turbulent characteristics of the flow were modeled using a low-Reynolds-number k-e turbulence model due to Launder and Sharma. The arbitrary nature of the computational domain was accounted for through the use of a nonorthogonal boundary-fitted coordinate system on a staggered grid. A control-volume-based finite difference scheme was used to solve the transformed transport equations. This study is primarily focused on elucidating the inlet superheat dissipation in the melt pool with the rolls being maintained at a constant liquidus temperature of the steel. A parametric study was carried out to ascertain the effect of the inlet superheat, t...

A Numerical Study of 3D Turbulent Melt Flow and Solidification in a Direct Chill Slab Caster with an Open-Top Melt Feeding System

A 3D control-volume based finite-difference model has been developed to simulate coupled turbulent melt flow and solidification phenomena for a semi-continuous direct chill slab casting of an aluminum alloy (AA-1050). The model considered an open-top melt delivery system for a hot-top mold. The model was verified with the experimental solidification front measurements and a reasonable agreement was found. The computations were carried out by varying important process parameters such as casting speed, inlet melt superheat, and mold–metal contact effective heat transfer coefficient in order to understand their effects on the solidification and cooling behavior of AA-1050.

NUMERICAL INVESTIGATION OF COUPLED TURBULENT FLOW, HEAT TRANSFER, AND MACROSCOPIC SOLIDIFICATION IN A VERTICAL TWIN-ROLL THIN-STRIP CASTER

A vertical twin-roll continuous thin-strip casting process for stainless steel has been mathematically modeled. The model takes into account the coupled turbulent flow, heat transfer, and macroscopic solidification aspects of the process. A low-Reynolds-number K-∊ turbulence model was used to account for the turbulent effects. The transport equations for the wedge-shaped casters cavity were solved using a boundary-fitted nanorthogonal coordinate system. A control-volume-based, iterative finite difference scheme on a staggered grid was used to solve the discretized transformed equations. The SIMPLE algorithm was employed to resolve the velocity-pressure coupling in the momentum equations. The parameters examined in this study include the Darcy coefficient and turbulent damping factor for the mushy region, the roll gap, and the inlet nozzle width. The effects of these process parameters on the turbulent flow and temperature fields, the turbulent eddy viscosity distributions, and the extents of the mushy an...

A numerical study of the complex dynamic behavior of a reactive gas bubble in water

Abstract It is recognized that, in nuclear reactors, oxygen-hydrogen gas bubbles may form and this formation can lead to an explosion hazard. In this study, numerical investigations are conducted into the collapse and explosion of an isolated oxygen-hydrogen bubble immersed in water. The mathematical model of the bubbles radial motion is based on the compressible form of the modified Rayleigh-Plesset equation of the bubble dynamics. The model also takes into account, in differential form, the heat transfer between the gas and the surrounding inert water. Parametric study on the present model is primarily aimed at delineating the effects of exothermicity of the reactive gas mixture and the initial bubble diameter on the bubbles volume and thermal oscillations under various sustained liquid pressure fields. The exothermicity of the bubbles gas content is varied by changing the mole fraction of the mixture of stoichiometric oxygen-hydrogen with the inert gas, argon, as a diluent. The results show that if the incident pressure pulse is not of sufficient strength, the mixture within the bubble does not ignite and the bubble radius remains below the initial equilibrium value throughout the pulsation period. Under the above conditions, due to the low heat capacity of argon compared to that of oxygen and hydrogen, the maximum gas temperature attained by the bubble increases with the increase in argon content or, equivalently, with the decrease in oxygen-hydrogen content. If the incident pressure pulse is strong enough, the bubble is seen to explode and the maximum gas temperature that the bubble attains depends directly upon the initial oxygen-hydrogen content. When the bubble undergoes ignition, with the increase of exothermicity, the maximum bubble radius increases and the period of the volume oscillation becomes longer. Also, with decreasing initial bubble radius, the liquid threshold pressure for bubble explosion increases, while the period of bubble oscillation decreases.

A Numerical Study of 3D Turbulent Melt Flow and Solidification in a Direct Chill Slab Caster with a Porous Combo Bag Melt Distributor

A 3D turbulent melt flow and solidification of an aluminum alloy (AA-1050) for an industrial-sized direct chill slab casting process is modeled. The melt is delivered through a rectangular submerged nozzle and a non-deformable combo bag fitted with a bottom porous filter. The non-Darcian model, incorporating the Brinkman and Forchheimer extensions, is used to characterize the turbulent melt flow behavior passing through the porous filter. The casting speed and the effective heat transfer coefficient at the metal–mold contact region within the mold are varied. The above two parameters are found to have significant influence on the solidification process.

Modeling of the melting characteristics of commercial paraffin wax in an inverted equilateral triangular enclosure: Effect of convective heat transfer boundary conditions

ABSTRACT A horizontal double-pipe heat exchanger with an inverted outer equilateral triangular tube is modeled to numerically investigate the low-temperature thermal energy storage capability of an impure phase change material (PCM). The energy source fluid (hot water) flows through the inner tube and transfers heat to the PCM (heat sink) residing in the annular gap. The results show that the inlet temperature of the heat transfer fluid (HTF) has a significant effect on the melting process compared with the mass flow rate (MFR). The configuration, as well the concentricity/eccentricity of the inner tube has a great influence on the energy storage.