High-speed high-strength fiber drawing

Journal of Heat Transfer

2013

This paper considers the thermal aspects that frequently arise in practical materials processing systems. Important issues such as feasibility, product quality, and production rate have a thermal basis in many cases and are discussed. Complexities such as property variations, complex regions, combined transport mechanisms, chemical reactions, combined heat and mass transfer, and intricate boundary conditions are often encountered in the transport phenomena underlying important practical processes. The basic approaches that may be adopted in order to study such processes are discussed. The link between the basic thermal process and the resulting product is particularly critical in materials processing. The computational difficulties that result from the non-Newtonian behavior of the fluid, free surface flow, moving boundaries, and imposition of appropriate boundary conditions are important in several processes and are discussed. Some of the important techniques that have been developed to treat these problems are presented, along with typical results for a few important processes. Validation of the model is a particularly important aspect and is discussed in terms of existing results, as well as development of experimental arrangements to provide inputs for satisfactory validation. The importance of experimentation and linking the micro/nanoscale transport processes with conditions and systems at the macroscale are discussed. Future trends and research needs, particularly with respect to new materials and new processes, are also outlined.

Section: Resultsmentioning

confidence: 86%

Thermal Issues in Materials Processing

Journal of Heat Transfer

2013

“…The effect of the meniscus on the flow field in the chamber, away from the meniscus, was found to be negligible. However, the flow very close to the meniscus was strongly affected [10].…”

Section: Resultsmentioning

confidence: 99%

“…As we move along the length of the convergent die the velocity profile tends to be flatter, being more so for the conical die. The taper of the die is restricted between 2 o -8 o as the self-centering force is maximized for the coating in this range [10]. Thus the die profile can be optimized for given flow rate, fluid and exit diameter to obtain gradual flow development and to avoid flow recirculation.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Simulation of the flow in a coating applicator for optical fiber manufacture

Rattan

Computational Mechanics

2003

A detailed numerical study is carried out on the flow field generated in an open-cup coating applicator during the coating process in the manufacture of optical fibers. This is a critical problem in the manufacture of optical fibers and poses several challenges to numerical modeling. A finite volume numerical model, using multiple domains to represent the fluid chamber and the die, is employed to obtain results on the flow. A coordinate transformation is used to model the complex geometry of the flow region. Fairly generic configurations are considered and a wide range of fiber drawing speeds, ranging up to 15 m/s, is investigated. Different boundary conditions, such as free and solid surface, at the entrance of the moving fiber are considered. Several coating materials are simulated, along with wide ranges of operating conditions and geometric designs. Though different temperatures are considered for the coating material, to obtain different fluid viscosities, the flow is considered to be isothermal. The focus is on the flow pattern and on the velocity fields in the fluid chamber and the die. Also, of interest are the resulting mass flow rate, which yields the final coating thickness, and the effects of the inlet conditions. The characteristics of the recirculating flow that arises in many cases are investigated in detail. The results are presented in terms of streamlines, velocity distributions and flow rates. The effects of geometry, coating material and die shape are investigated in detail. This is the first part of an on-going detailed study on the simulation of coating applicators for the manufacture of optical fibers in order to improve uniformity, consistency, and quality of the coating. List of Symbolsg Magnitude of gravitational acceleration (m/s 2 ) L Die or applicator length (m) p Pressure (Pascal) r Radial coordinate distance (m) R fiber Fiber Radius (m) R wall Radius at the applicator wall (m) R(z) Die radius profile (m) t Time (s) u Horizontal velocity (m/s) v Vertical velocity (m/s) z Axial coordinate distance (m)Greek Symbols q Density (kg/m 3

“…A downstream meniscus at the die exit results primarily from a balance between viscous and inertia forces, the surface tension being a relatively small effect. Interest lies in obtaining concentric coatings, of uniform thickness, and free of particle inclusions or bubbles (Paek, 1986).…”

Section: Numerical Simulationmentioning

confidence: 99%

Numerical simulation of complex transport phenomena arising in practical thermal systems

International Journal of Numerical Methods for Heat &Amp; Fluid Flow

2008

Purpose -This paper seeks to discuss the numerical modeling of the transport processes that frequently arise in practical thermal systems and involve complexities such as property variations with temperature or with the shear rate in the flow, complicated regions, conjugate mechanisms, chemical reactions and combined mass transfer, and intricate boundary conditions. Design/methodology/approach -The basic approaches that may be adopted in order to study such processes are discussed. Considerations for accurate numerical modeling are also discussed. The link between the process and the resulting product is critical in many systems such as those in manufacturing. The computational difficulties that result from the non-Newtonian behavior of the fluid or from the strong temperature dependence of viscosity are considered in detail. Similarly, complex geometry, free surface flow, moving boundaries, combined mechanisms, and simulation of appropriate boundary conditions are important in several processes and are discussed. Findings -Some of the important techniques to treat the problems that arise in numerical simulation are presented. Common errors that lead to inaccurate or invalid results are outlined. A few practical processes are considered in greater detail to quantify and illustrate these approaches. Validation of the numerical model is a particularly important aspect and is discussed in terms of existing results, as well as development of experimental arrangements to provide inputs for satisfactory validation. Originality/value -Practical thermal processes involve a wide variety of complexities. The paper presents some of the important ones and discusses approaches to deal with them. The paper will be of particular value to the numerical simulation of complicated thermal processes in order to design, control or optimize them to achieve desired thermal processing.