Heat and Mass Transfer in a CVD Optical Fiber Coating Process

Volume 3 ◽  
2004 ◽  
Author(s):  
Wei Huang ◽  
Wilson K. S. Chiu
Keyword(s):  
Heat Transfer ◽  
Optical Fiber ◽  
Reaction Kinetics ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Parameter Study ◽  
Inlet Temperature ◽  
Transfer Model ◽  
Phase Reaction ◽  
Empirical Parameter

In this paper, we study the chemical vapor deposition (CVD) process used to hermetically coat optical fibers during draw. Temperature is calculated by coupling radiation and convection heat transfer by the reactor walls and gas flow with a radially-lumped heat transfer model for the moving optical fiber. Multi-component species diffusion is modeled using the Maxwell-Stefan equations. Gas-phase reaction kinetics is modeled using a 2-step chemical kinetics mechanism derived from RRKM theory with detailed kinetics data compiled from literature. Surface reaction kinetics are described using collision theory in which a sticking coefficient is used as an empirical parameter to predict surface reactions. A parameter study is carried out with various optical fiber inlet temperature and drawing speed, and validated with experiment results.

Heat and Mass Transfer in a CVD Optical Fiber Coating Process by Propane Precursor Gas

2005 ◽  
Author(s):  
Wei Huang ◽  
Wilson K. S. Chiu
Keyword(s):  
Heat Transfer ◽  
Optical Fiber ◽  
Reaction Kinetics ◽  
Gas Phase ◽  
Gas Flow ◽  
Parameter Study ◽  
Inlet Temperature ◽  
Transfer Model ◽  
Phase Reaction ◽  
Empirical Parameter

This study investigates the chemical vapor deposition (CVD) process used to hermetically coat optical fibers during draw using propane as the precursor gas. Temperature is calculated by coupling radiation and convection heat transfer from the reactor walls and gas flow with a radially-lumped conduction heat transfer model for the moving optical fiber. Multi-component species diffusion is modeled by the Dixon-Lewis method, which is based on the molecular theory for ideal gases. Gas-phase reaction kinetics is modeled using a 3-step gas phase chemical kinetics mechanism. Surface reaction kinetics is described using collision theory in which a sticking coefficient is used as an empirical parameter to predict surface reactions. A parameter study is carried out with various optical fiber inlet temperature and drawing speed, and validated with experiment results.

Soret, Dufour and Heat by Chemical Reaction Effects in a Chemical Vapor Deposition Optical Fiber Coating Process

2005 ◽  
Author(s):  
Wei Huang ◽  
Wilson K. S. Chiu
Keyword(s):  
Heat Transfer ◽  
Chemical Vapor Deposition ◽  
Optical Fiber ◽  
Chemical Reactions ◽  
Vapor Deposition ◽  
Soret Effect ◽  
Chemical Vapor ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Transfer Model

In this paper, we studied the effect of thermal diffusion (Soret effect), the heat flux due to species concentration gradient (Dufour effect) and the heat by chemical reactions in a chemical vapor deposition (CVD) process used to hermetically coat optical fibers. Using a previously developed mass and heat transfer model to investigate the transport phenomena in this process, the Soret and Dufour effects are compared to ordinary mass diffusion. The thermal conductivity, molecular diffusivity and thermal diffusivity are calculated using a multi-component model. The contribution of heat of chemical reactions to overall heat transfer in the CVD is also discussed. Soret effect and heat by chemical reactions are found to be very important in this process, and their effect is related to operating conditions such as draw speed and optical fiber inlet temperature.

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.

scholarly journals Improving the W Coating Uniformity by a COMSOL Model-Based CVD Parameter Study for Denser Wf/W Composites

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1089
Author(s):  
Leonard Raumann ◽  
Jan Willem Coenen ◽  
Johann Riesch ◽  
Yiran Mao ◽  
Daniel Schwalenberg ◽  
...  
Keyword(s):  
Relative Density ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Process Time ◽  
Parameter Study ◽  
Reactor Model ◽  
Production Route ◽  
Coating Uniformity ◽  
Hydrogen Retention ◽  
Return Lead

Tungsten (W) has the unique combination of excellent thermal properties, low sputter yield, low hydrogen retention, and acceptable activation. Therefore, W is presently the main candidate for the first wall and armor material for future fusion devices. However, its intrinsic brittleness and its embrittlement during operation bears the risk of a sudden and catastrophic component failure. As a countermeasure, tungsten fiber-reinforced tungsten (Wf/W) composites exhibiting extrinsic toughening are being developed. A possible Wf/W production route is chemical vapor deposition (CVD) by reducing WF6 with H2 on heated W fabrics. The challenge here is that the growing CVD-W can seal gaseous domains leading to strength reducing pores. In previous work, CVD models for Wf/W synthesis were developed with COMSOL Multiphysics and validated experimentally. In the present article, these models were applied to conduct a parameter study to optimize the coating uniformity, the relative density, the WF6 demand, and the process time. A low temperature and a low total pressure increase the process time, but in return lead to very uniform W layers at the micro and macro scales and thus to an optimized relative density of the Wf/W composite. High H2 and low WF6 gas flow rates lead to a slightly shorter process time and an improved coating uniformity as long as WF6 is not depleted, which can be avoided by applying the presented reactor model.

Study on Effective Radial Thermal Conductivity of Gas Flow through a Methanol Reactor

2015 ◽  
Vol 13 (1) ◽  
pp. 103-112 ◽  
Author(s):  
Kun Lei ◽  
Hongfang Ma ◽  
Haitao Zhang ◽  
Weiyong Ying ◽  
Dingye Fang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Temperature Distribution ◽  
Large Scale ◽  
Gas Flow ◽  
Fixed Bed ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Particle Reynolds Number

Abstract The heat conduction performance of the methanol synthesis reactor is significant for the development of large-scale methanol production. The present work has measured the temperature distribution in the fixed bed at air volumetric flow rate 2.4–7 m3 · h−1, inlet air temperature 160–200°C and heating tube temperature 210–270°C. The effective radial thermal conductivity and effective wall heat transfer coefficient were derived based on the steady-state measurements and the two-dimensional heat transfer model. A correlation was proposed based on the experimental data, which related well the Nusselt number and the effective radial thermal conductivity to the particle Reynolds number ranging from 59.2 to 175.8. The heat transfer model combined with the correlation was used to calculate the temperature profiles. A comparison with the predicated temperature and the measurements was illustrated and the results showed that the predication agreed very well with the experimental results. All the absolute values of the relative errors were less than 10%, and the model was verified by experiments. Comparing the correlations of both this work with previously published showed that there are considerable discrepancies among them due to different experimental conditions. The influence of the particle Reynolds number on the temperature distribution inside the bed was also discussed and it was shown that improving particle Reynolds number contributed to enhance heat transfer in the fixed bed.

Flow Structure and Heat Transfer in Stagnation Flow CVD Reactor

2010 ◽  
Author(s):  
Nasir Memon ◽  
Yogesh Jaluria
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Atmospheric Pressure ◽  
Gas Flow ◽  
Flow Reactor ◽  
Chemical Vapor ◽  
Design Parameters ◽  
Stagnation Flow ◽  
Inlet Length ◽  
The Impact

An experimental study is undertaken to investigate the flow structure and heat transfer in a stagnation flow Chemical Vapor Deposition (CVD) reactor at atmospheric pressure. It is critical to develop models that predict flow patterns in such a reactor to achieve uniform deposition across the substrate. Free convection can negatively affect the gas flow as cold inlet gas impinges on the heated substrate, leading to vortices and disturbances in the normal flow path. This experimental research will be used to understand the buoyancy-induced and momentum-driven flow structure encountered in an impinging jet CVD reactor. Investigations are conducted for various operating and design parameters. A modified stagnation flow reactor is built where the height between the inlet and substrate is reduced when compared to a prototypical stagnation flow reactor. By operating such a reactor at certain Reynolds and Grashof numbers it is feasible to sustain smooth and vortex free flow at atmospheric pressure. The modified stagnation flow reactor is compared to other stagnation flow geometries with either a varied inlet length or varied heights between the inlet and substrate. Comparisons are made to understand the impact of such geometric changes on the flow structure and the thermal boundary layer. In addition, heat transfer correlations are obtained for the substrate temperature. Overall, the results obtained provide guidelines for curbing the effects of buoyancy and for improving the flow field to obtain greater film uniformity when operating a stagnation flow CVD reactor at atmospheric pressure.

Heat Transfer in the Non-reacting Zone of a Cement Rotary Kiln

1996 ◽  
Vol 118 (1) ◽  
pp. 169-172 ◽  
Author(s):  
P. S. Ghoshdastidar ◽  
V. K. Anandan Unni
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Rotary Kiln ◽  
Gas Flow ◽  
Transfer Model ◽  
Temperature Profiles ◽  
Gas Temperature ◽  
Gas Flow Rate ◽  
Steady State Heat ◽  
Steady State Heat Transfer

This paper presents a steady-state heat transfer model for a rotary kiln used for drying and preheating of wet solids with application to the non-reacting zone of a cement rotary kiln. A detailed parametric study indicates that the influence of the controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and the rotational speed of the kiln on the axial solids and gas temperature profiles and the total predicted kiln length is appreciable.

Conjugate Heat Transfer Enhancement of an Internal Blade Pin-Finned Tip-Wall

2009 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Conjugate Heat Transfer ◽  
Gas Flow ◽  
Turbine Blades ◽  
Thermal Design ◽  
Inlet Temperature ◽  
Computational Domain ◽  
Pin Fins ◽  
Blade Tip

To improve gas turbine performance, the operating temperature has been increased continuously. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Cooling methods are therefore needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to the hot gas flow and is difficult to cool. A common way to cool the tip is to use serpentine passages with 180-deg turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement. Increasing internal convective cooling is therefore required to increase the blade tip life. In this paper, augmented heat transfer of a blade tip with internal pin-fins has been investigated numerically using a conjugate heat transfer approach. The computational model consists of a two-pass channel with 180-deg turn and an array of pin-fins mounted on the tip-cap. The computational domain includes the fluid region and the solid pins as well as the solid tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within pins and tip are simultaneously computed. The inlet Reynolds numbers are ranging from 100,000 to 600,000. Details of the 3D fluid flow and heat transfer over the tip surface are presented. A comparison of the overall performance of the two models is presented. It is found that due to the combination of turning impingement and pin-fin cross flow, the heat transfer coefficient of the pin-finned tip is a factor of about 3.0 higher than that of a smooth tip. This augmentation is achieved at the cost of a pressure drop penalty of about 7%. With the conjugate heat transfer method, not only the simulated model is close to the experimental model, but also the distribution of the external tip heat transfer can be relevant for thermal design of turbine blade tips.

Catalytic Ignition Properties and Surface Reaction Kinetics Modeling From Methane in Oxygen-Nitrogen Mixtures on Platinum

2012 ◽  
Author(s):  
Duane Elgan ◽  
Judi Steciak ◽  
Ralph Budwig ◽  
Steve Beyerlein
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reaction Kinetics ◽  
Surface Reaction ◽  
Flow Reactor ◽  
Platinum Catalyst ◽  
Flow Simulation ◽  
Transfer Model ◽  
Measurement Capability ◽  
Surface Reaction Kinetics

The ignition temperature and heat generation from oxidation of methane on a platinum catalyst were determined experimentally. A 127 micron diameter platinum coiled wire was placed crosswise in a quartz tube of a plug flow reactor. A source meter with a 4-wire measurement capability measured the resistance and current to calculate the average temperature of the surface reaction. Light-off temperatures varied from 730–780K for methane for a fuel-oxygen equivalence ratio of 0.3 to 1.0 at fuel percentages of 2–5% by volume. A model of the experimental system was created using Fluent coupled with Chemkin to combine an advanced chemistry solver with flow simulation. The experimental data was compared to the model results, which includes heat transfer and the surface reaction kinetics of methane on platinum. The heat transfer model obtained values within 4 Kelvin to experimental data for temperatures between 400K and 700K. At temperatures greater than 700K the model deviated with temperatures greater than the experimental by up to 60 Kelvin.

Radiative Absorption in a Hollow Cylinder: Application to Microstructured Optical Fiber Fabrication

2004 ◽  
Author(s):  
Weixue Tian ◽  
Wilson K. S. Chu
Keyword(s):  
Heat Transfer ◽  
Optical Fiber ◽  
Hollow Cylinder ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Transfer Model ◽  
Participating Media ◽  
Microstructured Optical Fiber ◽  
Fiber Fabrication ◽  
Benchmark Solutions

Radiation absorption of an infinitely long hollow cylinder with Fresnel boundary is studied using the ray tracing method. Since the radiative heat transfer is the dominant heat transfer mode in optical fiber drawing, the current radiative transfer model can provide insights into physical processes for microstructured optical fiber fabrication. Effects of refractive index, optical thickness and geometry on radiative heat transfer are studied. The results of this study can also serve as benchmark solutions for radiative heat transfer for other methods, such as the finite volume method and the discrete ordinates method for participating media with Fresnel boundary.

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