Thermal transport due to material and gas flow in a furnace for drawing an optical fiber

1998 ◽  
Vol 13 (2) ◽  
pp. 494-503 ◽  
Author(s):  
S. Roy Choudhury ◽  
Y. Jaluria
Keyword(s):  
Heat Transfer ◽  
Optical Fiber ◽  
Temperature Difference ◽  
Thermal Transport ◽  
Transfer Rate ◽  
Gas Flow ◽  
Transport Processes ◽  
Inert Gas ◽  
Gas Velocity ◽  
Fiber Drawing

The transport processes involved in the neck-down region for optical fiber drawing are numerically investigated. In this manufacturing process, a moving glass rod is heated in a furnace containing an inert gas environment and drawn into a thin optical fiber. The conjugate problem is solved considering both radiation and convection, with focus on the latter. Two different flow configurations, involving inert gas flow in the same as well as in the opposite direction as the moving preform/fiber, are considered in this study. A coordinate transformation is used to change the complicated computational domains in the gas and the fiber to cylindrical ones. The transport in the fiber is coupled with that in the gas through the boundary conditions. The radiative thermal transport is calculated using an enclosure model developed in an earlier study. The numerical results on convective flow and transport are validated by comparing with results available in the literaturefor simpler configurations. The effects of several important parameters such as fiber draw speed, inert gas velocity, furnace dimensions, and gas properties on the flow and temperature distributions are investigated. For the aiding flow case, in which the inert gases flow in the same direction as the fiber, heat transfer to the fiber increases as the gas velocity increases. For opposing flow, a recirculating region appears in the gas, close to the moving fiber surface, causing reduction in heat transfer as compared to the aiding case. The thickness of this recirculating zone decreases with increasing inert gas velocity. Radiation is found to be the dominant mode of heat transfer in the overall heating of the preform/fiber, with nitrogen as the inert gas. However, near the edges of the furnace, radiation heat transfer is relatively small and convection becomes very important. Also, the convective transfer rate is relatively large near the flow entrance because of the large temperature difference between the gas and the fiber. However, away from the entrance, the gas heats up and the temperature difference relative to the fiber decreases, resulting in a smaller convective heat transfer rate. The relevance of the results to various aspects of the fiber-drawing process is discussed.

Thermal Transport and Flow in High-Speed Optical Fiber Drawing

1998 ◽  
Vol 120 (4) ◽  
pp. 916-930 ◽  
Author(s):  
Zhilong Yin ◽  
Y. Jaluria
Keyword(s):  
Optical Fiber ◽  
Thermal Transport ◽  
High Speed ◽  
Radiative Transport ◽  
Gas Velocity ◽  
Furnace Temperature ◽  
Fiber Drawing ◽  
Zonal Method ◽  
Optical Fiber Drawing ◽  
Purge Gas

The thermal transport associated with optical fiber drawing at relatively high drawing speeds, ranging up to around 15 m/s, has been numerically investigated. A conjugate problem involving the glass and the purge gas regions is solved. The transport in the preform/fiber is coupled, through the boundary conditions, with that in the purge gas, which is used to provide an inert environment in the furnace. The zonal method, which models radiative transport between finite zones in a participating medium, has been employed to compute the radiative heat transfer in the glass. The flow of glass due to the drawing process is modeled with a prescribed free-surface neck-down profile. The numerical results are compared with the few that are available in the literature. The effects of important physical variables such as draw speed, purge gas velocity and properties, furnace temperature, and preform diameter on the flow and the thermal field are investigated. It is found that the fiber drawing speed, the furnace temperature, and the preform diameter have significant effects on the temperature field in the preform/fiber, while the effects of the purge gas velocity and properties are relatively minor. The overall heating of the preform/fiber is largely due to radiative transport in the furnace and the changes needed in the furnace temperature distribution in order to heat the glass to its softening point at high speeds are determined.

Heat Transfer in Chemical Vapor Deposited Optical Fiber Coatings

2001 ◽  
Author(s):  
Patricia O. Iwanik ◽  
Wilson K. S. Chiu
Keyword(s):  
Heat Transfer ◽  
Optical Fiber ◽  
Gas Flow ◽  
Convection Heat Transfer ◽  
Fiber Surface ◽  
Chemical Vapor ◽  
Temperature Changes ◽  
Flow And Heat Transfer ◽  
Chemical Vapor Deposited ◽  
Fiber Coatings

Abstract A fundamental understanding of how reactor parameters influence the fiber surface temperature is essential to manufacturing high quality optical fiber coatings by chemical vapor deposition (CVD). In an attempt to better understand this process, a finite volume model has been developed to study the gas flow and heat transfer of an optical fiber as it travels through a CVD reactor. This study showed that draw speed significantly affects fiber temperature inside the reactor, with temperature changes up to 45% observed under the conditions studied. Multiple heat transfer modes contribute to this phenomena, with convection heat transfer dominating the process.

Effects of Various Reactions on the Gas Flow and Heat Transfer in an Anode Duct of ITSOFCs

2005 ◽  
Author(s):  
Jinliang Yuan ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Porous Electrode ◽  
Gas Permeation ◽  
Transport Processes ◽  
Operating Conditions ◽  
Electrochemical Reactions ◽  
Fuel Gas ◽  
Internal Reforming ◽  
Porous Anode

Recently, there has been considerable interest in the internal reforming reactions of solid oxide fuel cells (SOFCs) using methane or natural gas via. The internal reforming and electrochemical reactions appear in the porous anode layer, and may lead to inhomogeneous temperature and gas species distributions according to the reaction kinetics. A three-dimensional calculation method has been further developed to simulate and analyze the internal reforming and the electrochemical reactions, and the effects on various transport processes in a thick anode duct. In this study, the composite duct consists of a porous anode, fuel flow duct and solid current connector. Momentum, heat transport and gas species equations have been solved by coupled source terms and variable physical properties (density, viscosity, specific heat, etc.) of the fuel gas mixture. The combined thermal boundary conditions on solid walls, mass balances (generation and consumption) associated with the various reactions and gas permeation to/from the porous electrode are applied in the analysis. Simulation results show that the internal reforming and the electrochemical reactions, and operating conditions are significant for fuel gas transport and heat transfer in the anode.

Dynamic simulation of the circulating fluidized bed loop performance under the various operating conditions

2019 ◽  
Vol 233 (7) ◽  
pp. 901-913 ◽  
Author(s):  
Seongil Kim ◽  
Sangmin Choi ◽  
Jari Lappalainen ◽  
Tae-Ho Song
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Heat Transfer Rate ◽  
Dynamic Simulation ◽  
Transfer Rate ◽  
Gas Flow ◽  
Circulating Fluidized Bed ◽  
Operating Conditions ◽  
Temperature Behavior ◽  
Furnace Temperature

In a circulating fluidized bed boiler, the large thermal mass and flow characteristics of the solids strongly affect the transient response of the circulating fluidized bed loop temperature, which determines the heat transfer rate to steam flow. Therefore, it is essential to interpret the dynamic response of the solid behavior in the circulating fluidized bed loop for the stable and efficient operation of the circulating fluidized bed boiler. In this study, the dynamic simulation of the solid behavior along with the flue gas flow in a circulating fluidized bed loop was performed by applying the core-annulus approach for the solid-gas flow inside the furnace and selected models for other physical phenomena of the fluidized bed. The circulating fluidized bed loop of a commercial boiler was selected as the target system. Especially, the model simulates the characteristics of the solid behavior, such as the local solid mass distribution, and the solid flow inside the furnace and the circulating solid according to the various operating conditions. These aspects are difficult to measure and quantify in a real power plant. In this paper, the simulated furnace temperature behavior as the representative performance parameter of the circulating fluidized bed loop was discussed along with the qualitative operation experiences reported in the literature. The operating conditions include the feed rate of fuel and air, the particle size, the solid inventory and the solid circulation rate. Furnace temperature behavior was reproduced through the simulation for each operating case in the literature and was analyzed with the solid behavior along with the combustion rate and heat transfer rate of the circulating fluidized bed loop. The simulation enables quantitative evaluation of the effect of the solid behavior on the temperatures of the furnace and return part in the various operating conditions.

Einfluß der Strömungsform des Gases auf die chemischen Transportprozesse in Halogenglühlampen

1974 ◽  
Vol 29 (10) ◽  
pp. 1471-1477
Author(s):  
Gerhard M. Neumann
Keyword(s):  
High Pressure ◽  
Laminar Flow ◽  
Gas Phase ◽  
Flow Separation ◽  
Gas Flow ◽  
Chemical Transport ◽  
Transport Processes ◽  
Inert Gas ◽  
Good Accord ◽  
Incandescent Lamps

Abstract By raising the inert gas pressure and thus changing the type of gas flow chemical transport processes in tubular halogen incandescent lamps may be influenced. At medium pressures in the region of laminar flow separation of halogen and inert gas due to thermodiffusion occurs, the halogen cycle breaks down, and bulb blackening of the lamp is observed. At low and high pressure, where the streaming behaviour of the gas phase is dominated by diffusion or turbulence, separation of halogen and inert gas is overcome and the lamps stay clean. Observed pressures for changing from laminar to turbulent flow are 3.5 atm in xenon, 5.5 atm in krypton, and > 8 atm in argon in good accord with the well-known Reynolds' criterion.

Design and Analysis of a Heat Exchanger Network

2012 ◽  
Vol 9 (1) ◽  
pp. 85-91
Author(s):  
Mohammad Azim Aijaz ◽  
T. S. Ravikumar
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Temperature Difference ◽  
Transfer Rate ◽  
Outlet Temperature ◽  
Optimal Temperature ◽  
Heat Exchanger Network ◽  
Cold Fluid ◽  
Temperature Heat

the hot fluid outlet temperature, cold fluid outlet temperature, heat transfer rate and effectiveness at varying hot and cold fluid inlet temperatures using, log mean temperature difference (LMTD) and effectiveness-number of transfer units (ε-NTU) method. The obtained result illustrates how heat transfer rate and effectiveness increases or decreases at varying hot and cold fluid inlet temperatures. The result obtained from both LMTD and å-NTU method gives statistically significant values. The objective of this paper is to find out the optimal temperature at which heat transfer rate and effectiveness are maximum.

The UGKS Simulation of Microchannel Gas Flow and Heat Transfer Confined Between Isothermal and Nonisothermal Parallel Plates

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Lianfu Dai ◽  
Huiying Wu ◽  
Jun Tang
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Gas Flow ◽  
Flow Direction ◽  
Channel Height ◽  
Parallel Plates ◽  
Gas Temperature ◽  
Gas Velocity ◽  
Microscopic Mechanism ◽  
Flow And Heat Transfer

Abstract The unified gas kinetic scheme (UGKS) is introduced to simulate the near transition regime gas flow and heat transfer in microchannel confined between isothermal and nonisothermal parallel plates. The argon gas is used and its inlet Knudsen number (Knin) ranges from 0.0154 to 0.0715. It is found that: (1) both microchannel gas flows under isothermal and nonisothermal parallel plates display a trend of speed acceleration and temperature decrease along flow direction, for which the microscopic mechanism explanation is first proposed; (2) inlet gas streamlines under nonisothermal plates condition deviate from the parallel distributions under isothermal plates condition due to the dual driving effects of pressure drop along flow direction and temperature difference along cross section; (3) gas temperature, pressure, density and viscosity distributions along cross section under nonisothermal plates condition deviate from the parabolic distributions under isothermal plates condition, while the gas velocity keeps the parabolic distribution due to the effect of Knudsen layer; (4) as channel height increases or channel length and gas molecular mean free path decrease, the gas temperature distribution along cross section under nonisothermal plates condition tends to transition from linear to curve one due to the decreasing effect of heat transfer along cross section and increasing effect of gas acceleration along flow direction, this transition from linear to curve one becomes more obvious along flow direction. (5) the gas velocity under nonisothermal plates condition decreases with the increase of inlet gas temperature (Tin), lower plate temperature (Tl) and Knin, while the gas temperature increases with the increase of Tin, Tl and Knin.

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