Molten Glass Flow Research Articles

Numerical and experimental study of the effect of the induced electric potential in Lorentz force velocimetry

Lorentz force velocimetry (LFV) is a contactless velocity measurement technique for electrically conducting fluids. When a liquid metal or a molten glass flows through an externally applied magnetic field, eddy currents and a flow-braking force are generated inside the liquid. This force is proportional to the velocity or flow rate of the fluid and, due to Newton’s third law, a force of the same magnitude but in opposite direction acts on the source of the applied magnetic field which in our case are permanent magnets. According to Ohm’s law for moving conductors at low magnetic Reynolds numbers, an electric potential is induced which ensures charge conservation. In this paper, we analyze the contribution of the induced electric potential to the total Lorentz force by considering two different scenarios: conducting walls of finite thickness and aspect ratio variation of the cross-section of the flow. In both the cases, the force component generated by the electric potential is always in the opposite direction to the total Lorentz force. This force component is sensitive to the electric boundary conditions of the flow of which insulating and perfectly conducting walls are the two limiting cases. In the latter case, the overall electric resistance of the system is minimized, resulting in a considerable increase in the measured Lorentz force. Additionally, this force originating from the electric potential also decays when the aspect ratio of the cross-section of the flow is changed. Hence, the sensitivity of the measurement technique is enhanced by either increasing wall conductivity or optimizing the aspect ratio of the cross-section of the flow.

Selective laser melting of fiber-reinforced glass composites

A selective laser melting (SLM) process is developed for manufacturing of a novel glass fiber-reinforced glass (GRFG) composite material. Experiments using a continuous wave fiber laser are conducted for demonstrating this SLM process using borosilicate S-glass fibers and fine soda lime glass powders, which have distinct glass transition temperatures. During laser scanning, fine glass powders turn into viscous flow. The molten glass flows through and encapsulates the relatively solid fibers, which are not fused due to their relatively higher glass transition temperature. Upon cooling, a compacted GRFG composite forms with a high volume ratio of intact and well-encapsulated glass fibers.

Effect of Parameters of Isopipe on the Quality of Glass Sheet Produced from Overflow Fusion Process by Numerical Simulation

A numerical model for simulation of molten glass flow with semi-implicit method for pressure-linked equations (SIMPLE) and Volume of fluid (VOF) method during the overflow fusion process was carried out by using FLUENT software. The effect of the geometry parameters of the isopipe and flow rate of molten glass on the flow patterns during overflow was investigated. The results showed that the overflow trough depth only had an effect on the flow rate distribution of glass melt around the inlet point. The tilt angle at the top of the trough had a significant effect on flow rate distribution along the length of the trough, and the desired mass distribution was achieved at the tilt angle 4°∼6°. The flow rate had a large influence on the overflow of the molten glass, which had a directive significance to the overflow down draw sheet manufacturing process.

Simulation of Molten‐Glass Evolution from Spout Lip to Tin Bath

Viscous molten glass with a high temperature flows into a tin bath through a complicated three‐phase flow during the production of glass. It is very important to understand the characteristics of evolution for optimizing float‐glass design as well as preparing high‐quality flat glass. A three‐phase flow system containing molten glass, molten tin under N2/H2 atmosphere in a 600 t/day tin bath from the spout lip to the end of restrictor tile, was simulated and analyzed using ANSYS Fluent 14.0 software. The glass velocity field at the vertical section of the end of restrictor tiles, the relative position of glass material point between the entrance of tin bath and the vertical section of the restrictor tiles end, and the glass flow trend at the wetback area were analyzed. The edge of glass ribbon was formed by the bottom molten glass flow in the spout lip in contact with refractories, and greater proximity to the spout lip edge corresponded with greater proportion was supplied. The simulation indicates that the middle section of the glass cross‐section stria image can reflect the real glass location state at the canal vertical section and has little relationship with the tin bath.

Use of concentrated radiation for solar powered glass melting experiments

To investigate the feasibility of using concentrated solar radiation to provide process heat for glass production, a high flux solar simulator was used to melt glass forming batches. Initial experiments involved melting various glass forming batches which demonstrated that rapid and full conversion of the crystalline raw materials into an X-ray amorphous vitreous state was possible. A pure silica batch produced an X-ray amorphous product but it was not possible to refine the melt in these exploratory tests. A powdered, ternary soda–lime–silica (SLS) glass forming batch melted vigorously, with rapid gas removal, resulting in a completely transparent glass. Industrial SLS pellets were subsequently used in semi-continuous melting experiments, whereby the batch was intermittently fed into the melting zone while the beam was kept on. Additional secondary heating and insulation around outlet of the melting zone was required to achieve a semi-continuous flow of molten glass to an output crucible.

Kinetic model for quartz and spinel dissolution during melting of high-level-waste glass batch

The dissolution of quartz particles and the growth and dissolution of crystalline phases during the conversion of batch to glass potentially affects both the glass melting process and product quality. Crystals of spinel exiting the cold cap to molten glass below can be troublesome during the vitrification of iron-containing high-level wastes. To estimate the distribution of quartz and spinel fractions within the cold cap, we used kinetic models that relate fractions of these phases to temperature and heating rate. Fitting the model equations to data showed that the heating rate, apart from affecting quartz and spinel behavior directly, also affects them indirectly via concurrent processes, such as the formation and motion of bubbles. Because of these indirect effects, it was necessary to allow one kinetic parameter (the pre-exponential factor) to vary with the heating rate. The resulting kinetic equations are sufficiently simple for the detailed modeling of batch-to-glass conversion as it occurs in glass melters. The estimated fractions and sizes of quartz and spinel particles as they leave the cold cap, determined in this study, will provide the source terms needed for modeling the behavior of these solid particles within the flow of molten glass in the melter.

Numerical modeling on the discharged fluid flow from a glass melter by a Lagrangian approach

Abstract In Japan, it is planned to use vitrification to immobilize high level radioactive liquid waste (HLLW) obtained from the nuclear reprocessing process. In the vitrification process, the HLLW will be mixed with molten glass in a joule-heated glass melter. The molten glass is then poured into a canister through a nozzle at the bottom of the melter. When some abnormalities occurred, feature of the discharged flow become different from that in normal conditions. We cannot observe the state of the molten glass inside the melter directly because of the severe environment. Accordingly, we cannot investigate the cause when the abnormalities occurred. Hence, numerical simulation of the discharged flow becomes important to understand and recover from operational problems or abnormalities with the glass melter. However, existing numerical models of the glass melter do not really simulate the discharged glass flow. In the present study, we introduce a new algorithm into an existing Lagrangian approach to efficiently simulate the discharged glass flow. To verify the model, 3D simulations were performed on a real scale system and got compared with the results of experimental validation tests. The simulation results show good agreement with the experimental results. Consequently, the new Lagrangian approach accurately simulates the molten glass flow.

Molten glass flow stability during fiber drawing through a nozzle

We report a computer simulation study of the diameter uniformity of optical fibers produced by drawing through a nozzle. We determine the natural frequency and decrement of melt flow rate oscillations downstream of the nozzle and examine the effect of temperature ripple on deviations of the fiber diameter from its nominal value. It is shown that cooling the melt jet stabilizes the melt flow and the fiber diameter.

Method for Evaluating Thermal Convection in Molten Glass Flow in a Glass Tank Furnace

Various computer simulations of molten glass flow have been used for the design, operation and trouble shooting of glass tank furnaces. It is necessary to predict the degree of thermal convection of molten glass, whose viscosity is affected by the major composition of glass and thermal conductivity of which varies with the ferrous oxide (FeO) content. The thermal conductivity decreases as the FeO content increases. Thermal convection is characterized by the Rayleigh number, Ra, and the Prandtl number, Pr. Typically, Ra is expected to be large for a small thermal conductivity, but the actual thermal convection is weaker in this case than when the thermal conductivity is large. To elucidate the underlying convection mechanism, a two-dimensional mathematical flow model is developed in this study. Non dimensional formulation of the governing equations shows that Pr–1 affects the degree of thermal convection. The effective value of Ra, Raeff, is introduced to evaluate the influence of temperature-dependent properties on thermal convection. An evaluation method of thermal convection is proposed and extended to glasses with different thermal conductivities.

Thermoconvective flow of molten glass heated by direct induction in a cold crucible

Thermoconvective flow of molten glass heated by direct induction in a cold crucible

Effect of Isopipe Temperature on the Glass Sheet Forming for Overflow Fusion Process by Numerical Simulation

The overflow fusion process was an important method for the manufacture of glass sheet that is currently used for the production of TFT/LCD display devices. The design of forming apparatus was critical for very high surface quality of glass to allow the successful application of semiconductor type material. However, there is only a little of researches had been presented in the literatures, because of difficulties and expansions in experiments. In this study, a numerical model for simulation of molten glass flow through the isopipe during overflow fusion process was carried out. The effect of temperature of forming apparatus and of molten glass on the flow patterns during overflow fusion process was investigated. It was found that the stability and flatness of sheet glass was influenced strongly by the temperature of forming apparatus and molten glass. A precise control of overflow temperature and temperature distribution of isopipe was needed for maintaining a stable flow and uniform thickness.

Design of a sheet forming apparatus for overflow fusion process by numerical simulation

The overflow fusion process is an important method for the manufacture of glass sheets and is currently used for the production of TFT/LCD display devices. The design of the forming apparatus is critical for obtaining very high surface quality glass to allow the successful application of semiconductor type materials. However, there is only little work presented in the literatures, because of difficulties and expansions in experiments. In this study, a numerical model for simulation of molten glass flow through an isopipe during the overflow fusion process was carried out. An explicit finite difference algorithm with the surface tracking method has been proposed. The effect of the geometry of the forming apparatus, flow rate and viscosity of molten glass on the flow patterns during overflow was investigated. It was found that the stability and flatness of the sheet glass was influenced by the design of the forming apparatus, and the flow rate and viscosity of molten glass flow. The tilt angle at the bottom the of a trough should be high enough (5–7°) to avoid the accumulation of molten glass. The smaller root angle (<50°) was better for recombination of two stream of glass. High flow velocity will induce an unsteady flow profile along the wall of the isopipe. A precise control of the working temperature was needed for maintaining an equal thickness along the isopipe.

An integrated mathematical model of float process

Abstract An integrated mathematical model of the float process has been developed. This integrated model consists of a glass ribbon forming model, a float bath heat transfer model and a molten tin flow model. In the float process, glass ribbon forming and heat transfer in the bath influence each other. That is, the viscosity of the glass ribbon depends strongly on its temperature. Also, molten tin flow, which plays an important role in the bath heat transfer, is caused by glass ribbon traction and buoyancy convection. Therefore these three models are linked with one another. In the first model, the molten glass flow on the molten tin is simulated as viscous fluid flow. In the second model, three-dimensional radiative heat transfer is simulated. In the third model, three-dimensional turbulent flow of the molten tin is simulated. It is found that the simulated results are in good agreement with the measurements in the actual process. This integrated model can be used to study the mechanism in the float process, and moreover to optimize the operating conditions and to design float baths.

Large-scale numerical analysis of materials processing systems: High-temperature crystal growth and molten glass flows

Abstract We present Galerkin finite element computations of heat transfer and fluid dynamics in high-temperature materials processing systems. Examples are presented of how large-scale numerical simulations have been used to gain insight into the workings of several processes, specifically the growth of large, single crystals and the flow characteristics of molten glass. These systems are characterized by nonlinear interactions between field and interfacial phenomena — the transport of momentum, heat and mass and effects of solidification and capillarity. Additional complications are caused by the effects of internal radiative energy transport within participating media (internal radiation).

Application of the Radiotracer Method of Molten Glass Flow Process Identification for Optimization of Tank Furnaces

Some examples of application of the mathematical flow model proposed by Wolf and Resnick for the glass melting process optimization have been presented. The model description of the process was verified experimentally. The tracer selection criteria have been discussed. The method of radiotracer injection and the detection – recording apparatus have been described. The examples of parameters' values of the tank furnaces operation have been calculated. Tank furnaces of different design and final product were considered. Some general conclusions as well as technological recommendations formulated on the grounds of radiotracer investigations and with use of complex flow model of the molten glass have been presented.

Identification of the Molten Glass Flow Process in Tank Furnaces

Identification of the Molten Glass Flow Process in Tank Furnaces

Method for forming glass fibers

A glass fiber attenuation apparatus and process wherein molten glass is supplied from a molten glass body to an orifice plate at substantially atmospheric pressure to prevent molten glass flow through an orifice at which attenuation has ceased, thus permitting continuation of the attenuation process despite breakouts at individual orifices. The preferred embodiment of the method includes the steps of cooling the orifice plate undersurface to a non-wetting temperature and delivering molten glass to the orifice plate at a pressure less than the internal, surface tension-generated pressure of any bead formed on the undersurface of the orifice plate upon attenuation cessation at that orifice. The preferred embodiment of the apparatus includes a perforate pressure plate immersed in the body of molten glass and superimposed over the orifice plate to effect a pressure drop upon normal attenuation flow which is sufficient to reduce the pressure immediately above the orifice plate to substantially atmospheric pressure or, in any event, to a pressure less than the internal pressure of a bead or globule formed on attenuation cessation at an orifice. The orifice plate may be of either the planar, non-tipped type or of the tipped type, and the orifice plate may be cooled to the appropriate temperature either by gas flow cooling directed at the undersurface of the orifice plate or by fin shields.

Temperature control of poiseuille flow with particular application to flow of molten glass

The problem considered is that of controlling the temperature distribution of a fluid in fully developed laminar flow through a circular tube. It is assumed that suitable heating and cooling arrangements are available in a refractory casing surrounding the tube and that in its passage through a section of the tube of given length the mean temperature of the fluid has to be reduced (or increased) by a specified amount. The main feature of the problem lies in the additional requirement that the temperature distribution at the final cross-section must also be controlled to achieve some desired distribution. The problem is solved by application of optimal control theory. A quadratic cost functional is set up which includes a term measuring the closeness of fit to the desired exit temperature distribution and a constraint term to avoid unrealistic temperatures in the refractory. The solution is obtained by use of a Matrix-Riccati algorithm and also by dynamic programming. Numerical results are presented for a particular flow of molten glass. Typical exit and refractory temperature distributions are exhibited and the benefits of control are demonstrated. The results show clearly the extent to which the desired temperature distribution can be achieved for given available power.

The Manufacture of Continuous Glass Fibres

One of the most exacting applications of platinum is in the production of glass fibre. This involves the rapid flow of molten glass at temperatures around 1300°C through a series of small orifices which must retain their size and alignment. Current trends in the design of platinum alloy bushings are towards a greater output of fibre per unit weight of platinum employed.

ZGS PLATINUM

Abstract ZGS Platinum is a grain stabilized platinum containing a small amount of highly dispersed zirconium oxide. Its properties combine to provide greater high-temperature strength and, in some applications, greater contamination resistance than that of pure platinum. Applications include laboratory crucibles and dishes. An exacting application is in the production of fibre glass which invloved the rapid flow of molten glass at temperatures of 1250-1350 C through a pierced plate which must retain its shape and alignment. This datasheet provides information on composition, physical properties, microstructure, hardness, elasticity, and tensile properties as well as creep. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Pt-2. Producer or source: Matthey Bishop Inc..