Bath Surface Research Articles

Damped coalescence cascade of liquid drops

During coalescence of a drop with a liquid bath, the damped coalescence cascade (DCC) occurs due to local Marangoni flow generated on the bath surface. The local Marangoni flow accelerates air film drainage between the drop and the bath, leading to suppression of the rebound of daughter drops.

Prediction of decarburisation process along with hydrogen and nitrogen removal by mathematical modelling of RH degassing process

ABSTRACTThe decarburisation process is studied with the help of mathematical modelling of RH degasser with reaction interface area approach, considering multi-component mixed phase mass transport theory. An algorithm is developed by considering Ar gas, bath surface and CO gas bubbles as the reaction sites for decarburisation process. On the basis of this, the model is developed using MATLAB. The model is tested with five sets of data which are obtained from JSW Steel Plant Ltd. The results obtained from the model have been compared with the industrial data as well as the data obtained from literature survey. It is shown that the nitrogen and hydrogen removal are triggered more for higher CO evolution rate. The relations between carbon removal and factors like area of interface, time and vacuum pressure are proposed.

Determination of the True Temperature During Selective Laser Melting of Metal Powders Based on Measurements with an Infrared Camera

The recovery of the true temperature of a metal powder during selective laser melting is examined. A method is proposed for determining the temperature of the surface of the melt bath of a metal powder during selective laser melting based on measurements with an infrared camera. The influence of key melt parameters on the geometry of the melt bath is estimated.

Thermodynamic analysis and experimental study on the oxidation of the Zn-Al-Mg coating baths

Surface oxidation of molten Zn-6Al baths containing 0.0, 3.0 and 6.0wt. % Mg were analyzed using X-ray photoelectron spectroscopy. γ-Al2O3 is formed on the surface of the Zn-6Al bath, while MgAl2O4 and MgO occur at 460°C in the Zn-6Al-3Mg and Zn-6Al-6Mg baths, respectively. Thermodynamic analysis on the oxidation of the Zn-Al-Mg baths was performed. Calculated phase diagrams at 460°C and 560°C show good agreements with the experimental results. MgO or MgAl2O4 exists in almost the entire composition range of the calculated oxidation diagrams. According to the calculation, oxidation products depend on the composition and temperature of the baths. The primary and secondary oxidation products of the Zn-Al-Mg baths can be reasonably explained by oxidation phase diagrams. Utilizing these results, the favorable practical bath melts and operating conditions can be designed.

Biased flows in slab moulds induced by slide gates. Part I: experimental measurements and flow simulation

The effects of the slide or valve gate opening on the fluid flow of liquid steel in a slab mould, using a pyramid-bottom nozzle, were studied using water model and computer fluid dynamic approaches. When the valve gate opening is oriented towards the front broad face of the mould, the discharging jets impact first the back broad face, reach the narrow faces surrounding the mould and flow along the frontal broad face, providing natural biased flows. The combination of LES–VOF models is capable of simulating the flow patterns of water in the mould model as well as the topography of the free bath surface.

Understanding the Critical Parameters of the PAMS Mandrel Fabrication Process

In this paper, we describe the reasoning that leads us to focus on the so-called curing process where a solid poly(ɑ-methylstyrene) (PAMS) shell is formed from the initial solution phase. We demonstrate the existence of a percolation zone at about 55 wt% PAMS, beyond which the roundness of the shell can be expected to be irreversible. Using a simple model and a few supporting experiments to account for the rate of mass transfer of the fluorobenzene solvent phase, we show that curing rate is determined almost entirely by just a short exposure, to the sweeping gas, of the shells that graze the free surface of the curing bath as they move around in it. We propose here that specific control of the curing conditions at percolation would enable rounder mandrels.

Fundamental Investigation of E-Coat Systems for Next Generation Corrosion Control

Electrodeposition of coatings is widely used in the auto industry to protect against corrosion. Increased fundamental understanding is needed to enhance the effectiveness of coatings while decreasing the environmental risks associated with surface treatments and coatings, as well as the processes used to form them. In addition, the incorporation of fundamental understanding into modeling tools will help to improve the quality of predictions and ensure that the desired level of corrosion protection is achieved. Fundamentally based models can also provide insight to guide the development and use of new types of environmentally friendly surface pretreatments. Key parameters of interest to the present study include the coulombic efficiency (mass deposited per charge), the coating resistivity, bath conductivity, the degree of neutralization and the extent of amine substitution. The influence of operating conditions such as temperature and flow on these parameters is also critical. In this study, experiments are performed to investigate the influence of factors such as the degree of neutralization and the extent of amine substitution on the size of resin particles in solution and on the processes that render the resin insoluble, leading to deposition. Models are used to describe and quantify critical mechanisms. The impact of key parameters on the local deposition rate and on the coulombic efficiency is demonstrated. The ability to determine the local deposition rate is critical to the performance of large-scale systems and to our ability to predict that performance for a variety of bath compositions, operating conditions, and surface pretreatments.

Deceleration of droplets that glide along the free surface of a bath

A droplet obliquely impacting a bath surface of the same fluid can traverse along the interface while slowing at an exponential rate. The droplet rests on a thin film of air, deforms the bath surface creating a dimple and travels along the surface similarly to a wave pulse. Viscous coupling of the droplet and bath surfaces through the air film leads to viscous drag on the bath and perturbs the wave motion of the otherwise free surface. Even though the Reynolds numbers are greater than unity ($\mathit{Re}\,O(10{-}100)$), we show that the droplet’s deceleration is only due to viscous coupling through the air gap. The rate of deceleration is found to increase linearly with droplet diameter.

Inverse Leidenfrost Effect: Levitating Drops on Liquid Nitrogen.

We explore the interaction between a liquid drop (initially at room temperature) and a bath of liquid nitrogen. In this scenario, heat transfer occurs through film-boiling: a nitrogen vapor layer develops that may cause the drop to levitate at the bath surface. We report the phenomenology of this inverse Leidenfrost effect, investigating the effect of the drop size and density by using an aqueous solution of a tungsten salt to vary the drop density. We find that (depending on its size and density) a drop either levitates or instantaneously sinks into the bulk nitrogen. We begin by measuring the duration of the levitation as a function of the radius R and density ρd of the liquid drop. We find that the levitation time increases roughly linearly with drop radius but depends weakly on the drop density. However, for sufficiently large drops, R ≥ Rc(ρd), the drop sinks instantaneously; levitation does not occur. This sinking of a (relatively) hot droplet induces film-boiling, releasing a stream of vapor bubbles for a well-defined length of time. We study the duration of this immersed-drop bubbling finding similar scalings (but with different prefactors) to the levitating drop case. With these observations, we study the physical factors limiting the levitation and immersed-film-boiling times, proposing a simple model that explains the scalings observed for the duration of these phenomena, as well as the boundary of (R,ρd) parameter space that separates them.

Physical, chemical and thermal histories of an oxygen bubble in bath during bottom blown process

A mathematic model has been developed for an oxygen bubble rising in metal during a bottom blown process. The model successfully coupled local reactions and mass transport with heat transport between metal and the bubble surface, and between the latter and the bubble interior. This novel method reveals the physical, chemical and thermal histories of an oxygen bubble during a bottom blown process. An oxygen bubble rising in Fe–3%C metal under conditions of the oxygen bottom blown process was described by the modelling. The results show (1) the heat supplied to the bath is sourced from the secondary combustion in the bubbles rather than from the decarburisation at a bubble surface; (2) the temperature of a bubble surface reached a maximum of few degrees higher than the bath at few centimetres above the nozzle; (3) the maximum heat supplied to the bath by a bubble midway along the bubble trajectory is much more than the total heat supplied by the bubble reaching the bath surface; (4) the energy in the process-off gas is as high as three-fold of that received by the bath; and (5) iron is unlikely to be oxidised in front of the nozzle.

Study of cavity modes in BOF by analysis of sound

Various cavity modes (i.e. dimpling, splashing and penetrating) are important phenomena in estimating splashing in oxygen steelmaking. Though few studies in the literature have addressed this issue, no investigation can be found focusing on identifying modes by physical means. In the current work, sound produced in a cold air-water model was analysed to distinguish various cavity modes. Wave analysis showed that amplitude of sound increased as the mode changed from one to other. From spectrum analysis, it was found that between a certain range of frequencies, there was considerable difference in the sound level as the mode changed from splashing to penetrating. The presence of a second layer over the bath surface did not affect the general outcomes of the analysis. Present work indicates that it may be possible to identify cavity modes by analysing the sound produced from the bath. This would allow greater control of splashing in oxygen steelmaking and potentially help prevent slopping by controlling operation parameters of the process.

Boundary Conditions for Designing the Lining of a Glass-Founding Furnace with Innovative Parameters to Improve Technical Efficiency

This article presents results obtained from numerical modeling of external heat exchange in an innovative gas-fired glass-founding furnace with an output of 2.92 tons/m2·day). Unit heat consumption in the furnace is 4.187 MJ/kg. Boundary conditions are determined for designing and building a lining for the working space of the furnace. It is established that the average and maximum temperatures are 1512.6 and 1608.4°C for the roof, 1548.3 and 1596.3°C for the longitudinal wall (on the burner side of the furnace), and 1553.2 and 1622.2°C for the end wall (next to the flow). The average temperatures of the surface of the bath in the founding and fining zones are 1404.8 and 1426.6°C, respectively.

Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating

Abstract Due to increased demand for defect free, quality critical outer panel material for the automotive sector, continued focus on zinc coating quality is required. The snout area of a continuous galvanizing line is often a major source of coating issues with various surface defects arising from poorly understood and uncontrolled snout practices. This paper investigates the formation of a snout defect termed ‘the arrowhead defect’, named after its characteristic arrowhead shape. Defective samples have been characterised with the use of SEM/EDX and XRD and compared with contaminated sources collected from within the continuous galvanizing line snout. It is common practice to inject wet HNx into the snout in order to inhibit the production of zinc vapour. The wet HNx promotes the formation of a ZnO layer on the surface of the liquid zinc bath, preventing vaporisation and thereby reduces zinc dust contamination. The presence of ZnO, deliberately formed through the injection of wet HNx into the snout was observed within the arrowhead defect and can be identified as the root cause of this defect. Discrete contamination particles were entrained within the tail of the defect. XRD patterns of both the defect & snout contamination have been presented to discern the nature of the contamination entrained within the zinc coating. Characteristic ZnO peaks were observed at θ = 32° for both surface contamination and at increasing penetration depths within the coating in the region of the arrowhead defect. The inclusion of the arrowhead defect in Full Finish material led to an increase in the rate of corrosion 2.5 × that of the corrosion rate on non-defective material, highlighting the need to produce defect free galvanized steel for both aesthetic and corrosion purposes. Whilst the injection of wet HNx as a method of suppressing the formation of zinc vapour is a long standing process for automotive Full Finish production, due to the nature of these oxide-based defects, this process is in fact a “double edged sword” in that it solves one problem but can create another. Alternative techniques to suppress zinc vapour formation should be investigated to further drive up the quality of zinc coatings for automotive applications.

Cellular Automata Modeling of Decarburization of Metal Droplets in Basic Oxygen Steelmaking

In steelmaking, a supersonic jet is blown over the bath to refine the hot metal to produce steel. The refining process primarily consists of removal of impurities from the hot metal to a permissible level. The impact of oxygen jet on the surface of the hot metal bath results in ejection of droplets, which mix with slag and form emulsion. The formed emulsion plays an important role in refining reactions kinetics and understanding of this process is required todevelopimproved process control model for the steel industry. In this paper, cellular automata technique has been explored to simulate decarburization in emulsion caused by interfacial reactions between the metal droplets and slag. In the course of the work, a framework has also been developed to quantify the contribution of carbon monoxide, generated by decarburization, in bloating of metal droplets and formation of halo around the droplets. The model has incorporated diffusion and decarburization reaction based on probabilities to study the evolution of the system. Simulations with varying parameters have been performed and decarburization trends obtained are comparable with the experimentally determined data reported in literatures.

Understanding of Bath Surface Wave in Bottom Blown Copper Smelting Furnace

The waves formed on bath surface play an important role in the bottom blown copper smelting furnace operations. Simulation experiments have been carried out on model of the bottom blown furnace to investigate features of the waves formed on bath surface. It was found that the ripples, the 1st asymmetric standing wave and the 1st symmetric standing wave were able to occur in this model, and empirical occurrence boundaries have been determined. The amplitude and frequency of the standing waves have been systematically investigated. It was found that the amplitude of the 1st asymmetric standing wave is much greater than the 1st symmetric standing wave and the ripples; and the amplitude is found to increase with increasing bath height and flowrate but decrease with blowing angle. The frequency of the 1st asymmetric standing wave is found increasing with bath height but independent of flowrate and blowing angle.

Experimental and Numerical Analysis of the Deformation of a Liquid Aluminum Free Surface Covered by an Oxide Layer During Induction Melting

In an induction furnace, as a result of electromagnetic forces, the free surface of a liquid aluminum bath deforms and takes the form of a dome. The oxide layer that forms spontaneously on the free surface of aluminum melts may also influence the deformation by exerting an additional friction force on the metal. A non-intrusive experimental technique—Structured Light Fringe Projection—was used to measure the complete surface deformation and its fluctuations, for a varying set of operating parameters—inductor current intensity and initial liquid metal filling level inside the crucible. For an axisymmetric geometry, numerical simulations were carried out to calculate in a single framework: (i) the electromagnetic forces using the A–V formulation, (ii) the free surface deformation using the Volume of Fluid method, and (iii) the turbulent stirring of the metal using a RANS-based k–ω model. The friction force due to the oxide layer was modeled by imposing a pseudo-wall condition on the free surface, which makes the interfacial velocity very small compared to the average liquid metal pool velocity. A marked impact on the dome height due to applied friction force is observed. Finally, comparisons between the predicted and measured domes are presented.

Novel light-weight, high-performance anode-supported microtubular solid oxide fuel cells with an active anode functional layer

Influence of the air-gap, the distance from the tube-in-orifice spinneret to the upper surface of the external coagulant bath during the extrusion/phase-inversion process, on the microstructure of nickel – yttria-stabilized zirconia (Ni–YSZ) hollow fibers has been systematically studied. When the air-gap is 0 cm, the obtained Ni–YSZ hollow fiber has a sandwich microstructure. However, when the air-gap is increased to 15 cm, a bi-layer Ni–YSZ hollow fiber consisting of a thin layer with small pores and a thick support with highly porous fingerlike macrovoids has been achieved. The output power density of microtubular solid oxide fuel cells (MT-SOFCs) with a cell configuration of Ni–YSZ/YSZ/YSZ–LSM increases from 594 mW cm−2 for the cells with the Ni–YSZ anode of sandwich microstructure to 832 mW cm−2 for the cells with the Ni–YSZ anode of bi-layer microstructure at 750 °C, implying that to achieve the same output power density, the weight of the cells with the bi-layer anode support can be reduced to 41.5% compared with that of the cells with the sandwich anode support. Thermal-cycling test shows no obvious degradation on the open-circuit-voltage (OCV), indicating that the MT-SOFCs have robust resistance to thermal cycling.

Multiphase Numerical Model of Molten Steel and Slag Behavior in the Continuous Casting Mould

AbstractThe paper reports the results of numerical simulation of the flow of liquid steel with the use of a multiphase model. The facility under study was a mould designed for continuous casting of steel slabs. The geometry of the facility, along with the computational grid, was generated within the program Ansys-MeshingR. Numerical computations were performed in the programs: COMSOL Multiphysics¯ and Ansys-Fluent¯. The use of the multiphase model enabled the determination of the behavior of the liquid slag layer on the metal bath surface. From the performed computer simulations, the fields of liquid steel motion and liquid steel turbulence kinetic energy distribution in the mould's symmetry plane have been presented. Based on the values recorded at selected measurement points located on the slag surface, a diagram illustrating the variation of the slag layer position during continuous steel casting has been plotted.

機械撹拌式溶銑脱硫反応へ及ぼす脱硫剤添加方法の影響

Effect of a flux addition method on hot metal desulfurization by a mechanical stirring was investigated in a 1/12-water model and a 70 kg hot metal desulfurization tests. Following flux addition method was employed; top addition on bath surface at the first period of desulfurization, continuous addition from the top and powder blasting with nitrogen gas. Desulfurization rate of powder blasting is larger than continuous addition and top addition. The obtained aggregated slag (desulfurization flux) particle diameters after desulfurization were 0.76 mm (top addition) and 0.38~0.44 mm (powder blasting), respectively. Desulfurization behavior was analyzed assuming the interfacial area between the flux and the hot metal is proportional to the estimated aggregated slag particle size. Based on the analysis, the effect of powder blasting with nitrogen gas on improvement of desulfurization efficiency was interpreted to be the combined results of a) promotion of flux dispersion, avoiding aggregation at the time of flux addition and b) prevention of slag particle aggregation in hot metal during stirring.

Effect of Flux Addition Method on Hot Metal Desulfurization by Mechanical Stirring Process

The effects of three flux addition methods on hot metal desulfurization with mechanical stirring were investigated in a 1/12-water model test and a 70 kg hot metal desulfurization test. The flux addition methods studied here were top addition on the bath surface in the first period of desulfurization (batch addition), continuous addition from the top, and powder blasting with nitrogen gas. The desulfurization rate when powder blasting is applied is larger than that of either continuous addition or batch addition. The obtained aggregated slag (desulfurization flux) particle diameters after desulfurization were 0.76 mm (batch addition) and 0.38–0.44 mm (powder blasting). Desulfurization behavior was analyzed assuming that the interfacial area between the flux and the hot metal is proportional to the estimated size of the aggregated slag. Based on this analysis, the effect of powder blasting with nitrogen gas on improvement of desulfurization efficiency was interpreted to be the combined result of a) promotion of flux dispersion and avoiding aggregation during flux addition and b) prevention of slag particle aggregation in the hot metal during stirring.