In this paper, a macroscopic mathematical model is developed for simulation of transport phenomena during ternary alloy solidification processes, taking into account non-equilibrium effects due to ...solutal undercooling. The model is based on a fixed-grid, enthalpy-based, control volume approach. Microscopic features pertaining to non-equilibrium effects on account of solutal undercooling are incorporated through a novel formulation of a modified partition coefficient. The effective partition coefficient is numerically modeled by means of macroscopic parameters related to the solidifying domain. Numerical simulations are performed for ternary steel alloy by employing the present model and the resulting convection and macrosegregation patterns are analyzed. It is observed that the consideration of non-equilibrium solidification in the present mathematical approach is able to capture the thermo-solutal convection and leads to prediction of accurate value of macrosegregation. The results from the present model matches well with the experimental observations published in the literature.
The macro-scale segregation of alloying elements during the casting continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. ...Defects such as A-segregates are still commonplace, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today’s steel ingots are as chemically homogeneous as possible.This article briefly reviews the development of our current understanding of macrosegregation phenomena during the 20th century, before going on to assess the latest developments in the field of macrosegregation modelling. The aim of the text is to highlight the shortcomings of applying contemporary macromodels to steel-ingot casting, and to suggest practical alternatives. In addition, the experimental characterisation of macrosegregation is explored, and a review of the various techniques currently available is presented.
With the vigorous development of the electronics industry today, study on the recycling of electronic waste has become an important and urgent subject nowadays. However, more work should be done on ...purification of recycled metal, especially metallurgical approaches which are more environmentally friendly. This study proposed a continuous metallurgic purification method to remove impurities from recycled aluminum. Numerical study via multiphase modelling was conducted to evaluate and optimize the purification efficiency of this metallurgic method. Parametric study was carried to analyze the influence of mold temperature and casting speed on purification efficiency. The simulation results showed that the method has great potential for purification of recovered metals, refining the aluminum from 2 N to 3 N within three cycles. The formation mechanism of Si macrosegregation region in the outer region of the rod has been discussed in detail, which indicates the key factor of the melt flow at the solidification front. The problem of purification process purely via thermal-solutal flow was stated and traveling magnetic field was introduced to further increase the purification efficiency. In general, this work provides a verified promising continuous metallurgical purification method for impurities removal from recycled aluminum.
Numerical simulations can provide insight into physical phenomena during alloy solidification processes that cannot be observed experimentally. These model predictions depend on the material, process ...and numerical parameters which contain inherit uncertainties due to their origin in experimental measurements or model assumptions. As a step towards understanding the effect of uncertain inputs on solidification process modelling, uncertainty quantification and sensitivity analysis are performed on a transient model of transport phenomena during the solidification of grain refined Al-4.5 wt.% Cu in a rectangular cavity. The effect of microstructural model parameters, thermal boundary conditions and material property input uncertainties are examined for their effect on macrosegregation levels and solidification time. Predictions of the macrosegregation level are most sensitive to the dendrite arm spacing of the rigid mushy zone.
In this work, we developed a numerical approach based on an experimental platform to determine the working conditions on a cryoplatform and to predict and evaluate the cryogenic printing of ...hydrogels. Although hydrogels have good biocompatibility, their material properties make it difficult to print them with high precision and shape fidelity. To overcome these problems, a cryogenic cooling platform was introduced to accelerate the physical stabilisation of each deposited layer during the printing process. By precisely controlling solidification (crystallisation), each printed material can withstand its own weight to maintain shape fidelity, and the porosity of the scaffolds can also be controlled more selectively. The thermophysical properties of gelatine hydrogels were investigated to gain a better understanding of the phase change upon freezing. The corresponding material properties and experimental observations of gelatine solidification served as the basis for developing a computational fluid model (CFD) to mimic the solidification of gelatine hydrogels using a cryoplatform at different process conditions and extruder speeds. The goal was to develop a tool simple enough to predict acceptable process conditions for printing gelatine hydrogels using a cryoplatform.
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•Coupled FVM-CA multi-scale solidification model for simulation of 3D grain-structure.•A new macroscopic averaging strategy for predicting the CET and ECT Events.•Establishing process ...parameters and grainstructure relationship for a casting process.•Instantaneous grain-growth lines match very well with the simulated grain structure.
Understanding of columnar-to-equiaxed transition (CET) and equiaxed-to-columnar transition (ECT) is difficult not only due to the involvement of multiple factors like advection of equiaxed grains, fragmentation of dendrites, etc. but also due to its complex relationship with temperature gradient (G), solidification velocity (R), and cooling rate (Ṫ) at the solidification front over a broad range of solidification conditions. Parametric multi-scale, multiphysics grain structure simulations were performed to develop the relationship between process-parameters and grain structure for the casting process over a wide range of process parameters. The effect of interfacial heat transfer coefficient, superheat, and nucleation site density on the grain structure is studied using a coupled finite-volume-method-cellular-automaton (FVM-CA) multi-scale, multiphysics solidification model. A numerical averaging strategy at the solidification front is proposed for monitoring the occurrence of CET and ECT. We attempt to study the grain structure evolution obtained from the multi-scale model with the transient macroscopic average thermal parameters. Unlike the previous attempts here we evolve criteria independently from the macro-model that obeys the phase diagram. It was found that the temperature field has the imbibed signatures for the occurrence of CET and ECT.
In this paper, a macroscopic mathematical model is developed for simulation of transport phenomena during ternary alloy solidification processes, taking into account non-equilibrium effects due to ...solutal undercooling. The model is based on a fixed-grid, enthalpy-based, control volume approach. Microscopic features pertaining to non-equilibrium effects on account of solutal undercooling are incorporated through a novel formulation of a modified partition coefficient. The effective partition coefficient is numerically modeled by means of macroscopic parameters related to the solidifying domain. Numerical simulations are performed for ternary steel alloy by employing the present model and the resulting convection and macrosegregation patterns are analyzed. It is observed that the consideration of non-equilibrium solidification in the present mathematical approach is able to capture the thermo-solutal convection and leads to prediction of accurate value of macrosegregation. The results from the present model matches well with the experimental observations published in the literature.
•The transport quantities dedicated to the fine fragmentation process are proposed.•The source terms of transport equations are introduced and discussed.•The approach how to implement the model into ...the Eulerian MC3D code is proposed.•The solidification effect on the vapour explosion strength is demonstrated.
Melt droplet solidification is one major phenomenon acting on the mitigation of the strength of vapour explosions in situations related to nuclear safety. The modelling of solidification effects is then an important challenge for the evaluation of fuel–coolant interaction. We present an attempt for modelling the crust that might develop around melt droplets and its effect on the fine fragmentation within an Eulerian formulation of the flow equations, with application to the MC3D code.
A physically-based modelling of the melt droplets temperature profile and a fragmentation criterion for partly solidified droplets are presented. The implementation of these models in the specific case of Eulerian modelling of the melt droplet phase is described. Two additional transported model parameters based on the most important droplets features regarding the fuel–coolant interaction behaviour are derived. The first property to transport is the crust stiffness because it enables the correct prediction of the amount of droplets participating in the droplet fragmentation process. The second is related to the energy transfer from the droplet interior to the surface. This enables to improve the surface temperature determination and reflects the history of the droplet cooling. Also the potential effect of solidification on the vapour explosion strength is shown.
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