Sudip Simlandi

Heatline Visualization During Solidification of a Eutectic Solution in a Rectangular Cavity

The present work is focused on the visualization of heatline during solidification. The investigation considers a rectangular cavity filled with eutectic aqueous ammonium chloride solution. In order to develop Rayleigh-Bennard convection in the cavity, the temperatures of the top and bottom walls are maintained below and above eutectic temperature of the solution, respectively, whereas the vertical walls are assumed to be adiabatic. The solidification process is modelled by a set of mass, momentum and energy conservation equations coupled with boundary conditions. The governing differential equations are solved using semi-implicit finite volume method according to SIMPLER algorithm with the help of line-by-line TDMA solver. The evolution of heatline pattern during solidification is presented. From the evolution of solid–liquid interface, it is found that the solidified layer undergoes remelting at the solid–liquid interface during later stages of solidification as a consequence of thermal superheat. In the present work, the cause of the remelting phenomenon during solidification is investigated in details using energy flux vectors. It is observed that convection loop pattern i.e. energy flow below the remelted interface changes at the time of remelting.

Studies on Transport Phenomena during Continuous Casting of an Al-Alloy in Presence of Electromagnetic Stirring

In the present work, a numerical study is performed to predict the transport phenomena during continuous casting of an aluminum alloy (A356) in presence of weak stirring. A set of volume averaged single phase conservation equations (mass, momentum, energy and species) is used to represent the casting process. The electromagnetic forces are incorporated in the momentum equations. The governing equations are solved based on the pressure-based finite volume method according to the SIMPLER algorithm using TDMA solver along with an enthalpy update scheme. The simulation predicts the temperature, solid fraction and species in the computational domain. A parametric study is also performed.

Study on Rheological Behavior of Semisolid A356 Alloy During Solidification

In the present work, a model is developed to predict the rheological behavior of an Al-alloy (A356) in semisolid state where the alloy is sheared between two parallel plates during continuous cooling. The flow field is represented by the momentum conservation equation where the non-Newtonian behavior of the semisolid alloy is incorporated considering the Herschel–Bulkley model. In the slurry, the agglomeration and de-agglomeration phenomena of the suspended particles under shear are represented using a time dependent structural parameter. The temperature field during cooling is predicted considering the transient energy conservation equation, and hence the fraction of solid and the yield stress of the semisolid alloy are continuously updated. Considering an apparent viscosity of the semisolid alloy as a function of structural parameter, shear stress and shear rate, the governing equations are solved analytically. Finally, the work predicts the variation of the apparent viscosity of the semisolid A356 alloy with fraction of solid. At first, the present prediction is validated against an available experimental data and, thereafter, the work predicts the effect of process parameters such as shear rate and cooling rate on the apparent viscosity.

Study on Thixotropic Property of A356 Alloy in Semi-Solid State

In the present work, the thixotropic property of a semisolid aluminium alloy (A356) under deformation is investigated numerically where the Couette flow between two parallel plates is considered. The flow field is represented by momentum conservation equations where the non-Newtonian behavior of the semisolid material is represented by the Herschel-Bulkley model. The agglomeration and the de-agglomeration phenomena of the suspended particles under shear are represented using a time dependent structural parameter influenced by the rate of strain and shear stress. The simulation predicts the flow field, rate of strain and apparent viscosity of the semisolid materials under transient and steady state conditions. It is found that the apparent viscosity shows a transient nature during sudden change in the shear rate, and its value decreases with increasing shear rate and vice-versa. It is also found that the present prediction shows a good agreement with prior work.

Numerical investigation on cooling behaviour of buildings using phase change material

This work considers cooling of buildings using a suitable PCM on its rooftop in a hot climate country. The PCM absorbs solar radiation by melting in day time and releases absorbed heat by solidification at night to the ambient. Both melting and solidification involve complex transport phenomena those are governed by mass, momentum and energy conservations. For simulation, the set of governing equations is discretised based on control volume method using power law scheme. Finally, the SIMPLER and TDMA algorithms are used to solve the discretised linear algebraic equations. The two-phase interface during melting and solidification is traced using enthalpy update scheme. Prediction involves melting, solidification behaviours of PCM, and variation of room temperature throughout the day. As observed, the recycling of PCM is possible for the next successive days if thermal conductivity enhancer (TCE) is added in PCM. Accordingly, a TCE is considered for recycling of the PCM.

Behaviour of Semisolid Slurry Flows through a Channel

In case of metal sheet forming of alloys in semisolid state, modelling of the process is very essential to predict flow behaviour, temperature distribution of the alloy etc. towards improvement of the product quality and to reduce manufacturing costs. Accordingly, the present work develops a model to predict the behaviour during metal sheet forming of an Al-alloy (A356) in semisolid state. The semisolid alloy passes through a rectangular channel having small depth and larger width. The alloy in semisolid state is cooled from the top at a controlled rate. In the model, the respective flow field is represented by the momentum conservation equation. The non-Newtonian behaviour of the semisolid slurry is incorporated considering the Herschel–Bulkley model. The agglomeration and de-agglomeration phenomena of the suspended particles under shear are represented using a time dependent structural parameter. The temperature field is predicted considering the transient energy conservation equation, and hence the fraction of solid is continuously updated. The solution considers an apparent viscosity of the semisolid alloy as a function of structural parameter, shear stress and shear rate. The governing equations are finally solved by finite difference method. The work predicts velocity, temperature and liquid fraction distribution of the semisolid slurry.

Modelling of Extrusion Process for Aluminium A356 Alloy

In the present work, a model is developed to study extrusion process of A356 alloy in semi-solid state. The distinct rheology of the semisolid alloy reduces energy necessity during extrusion process. Accordingly, a proper rheological model of the alloy is considered in the model towards a detailed study of the process. A combination of analytical and numerical solutions is considered for solving the governing equations. The work finally predicts distribution of velocity and shear stress of the alloy under shear in the considered domain. It also predicts the energy requirement during the extrusion process. It is demonstrated that for semisolid extrusion, reasonably less energy is required as compared to a conventional extrusion process Keywords: Extrusion, semi-solid alloy, apparent viscosity, extrusion power

Studies on Double Diffusive Convection and Macro-segregation During Solidification of an Al-Alloy Based on Macro–Micro Model

In the present work, a study on the double diffusive convection and the macro-segregation during solidification of an Al-alloy (A356) is considered based on the macro–micro model. The model considers a volume average single-domain approach to represent all the variables and properties as continuum in the entire domain where the transport phenomena during solidification are represented by mass, momentum, energy and species conservation equations. The evolution of solid during solidification, in the model, is predicted based on the microscopic phenomena, i.e. considering the nucleation and the growth of the nuclei. A semi-implicit finite volume method is adopted to discretize the governing equations and the discretized linear simultaneous equations are solved based on the SIMPLER and the TDMA algorithms. The simulation involves prediction of temperature, velocity and species in the computation domain during solidification of the alloy. A parametric study is also considered.