RADIATIVE CHARACTERISTICS OF A THIN SOLID FUEL AT DISCRETE LEVELS OF PYROLYSIS: ANGULAR, SPECTRAL, AND THERMAL DEPENDENCIES by RICHARD DALE PETTEGREW Submitted in partial fulfillment of the requirements For the Degree of Doctor of Philosophy Thesis Advisors: Professor James S. T’ien (CWRU) Dr. Kenneth Street (NASA GRC) Department of Mechanical and Aerospace Engineering CASE WESTERN RESERVE UNIVERSITY January, 2006 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the dissertation of ______________________________________________________ candidate for the Ph.D. degree *. (signed)_______________________________________________ (chair of the committee) ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. Copyright 2005 by Richard Dale Pettegrew All rights reserved i Dedication This work is dedicated to the loving memory of my mom and dad, Carroll and Lowell Pettegrew. They taught me to dream big, take risks when necessary, and have the kind of work ethic needed to finish a project like this. Even more importantly, they believed in me when no one else did. While they are no longer here to see the completion of this work, I believe they know, and are proud. Mom and Dad: I love you both, and thank you for everything! i Table of Contents Dedication ........................................................................................................................... i List of Tables .................................................................................................................... iv List of Figures.................................................................................................................... v Acknowledgements .........................................................................................................vii Abstract...........................................................................................................................viii 1.0 Introduction........................................................................................................... 1 1.1 Radiative Heat Transfer in Combustion Problems........................................................................... 2 1.2 Gas-Phase Radiation ........................................................................................................................ 4 1.3 Surface Radiation............................................................................................................................. 6 1.3.1 Reasons for Spectral Dependence .......................................................................................... 7 1.3.2 Temperature Dependence & Thermal Effects......................................................................... 8 1.3.3 Angular Dependence............................................................................................................ 10 1.4 Radiative Interaction between Gas and Solid................................................................................. 10 1.5 Previous Knowledge of Optical Properties .................................................................................... 11 1.6 Objectives of This Study................................................................................................................ 13 2.0 Experimental Approach & Overview ............................................................... 16 2.1 Premise and Assumptions.............................................................................................................. 16 2.2 Data Acquisition and Determination of Spectral Properties........................................................... 18 2.3 Determination of Band-Integrated Properties ................................................................................ 21 2.4 Determination of Activation Energy and Pre-Exponential Factor ................................................. 22 3.0 Hardware & Procedures .................................................................................... 23 3.1 Sample Material and Preparation................................................................................................... 23 3.1.1 Sample Materials.................................................................................................................. 23 3.1.2 Sample Preparation.............................................................................................................. 25 3.1.3 Heat-Treatment Furnace ...................................................................................................... 27 3.2 FTIR Instruments and Procedure ................................................................................................... 28 3.2.1 Integrating Sphere................................................................................................................ 29 3.2.2 External Sample Mounting: Normal Incidence Hemispherical Measurements.................... 34 3.2.3 External Sample Mounting: ‘Forward Scattered’ Measurements........................................ 35 3.2.4 Internal Sample Mounting: Normal and Angular Incidence Measurements........................ 37 3.3 ‘Sample Blanking’: Accounting for Light Losses, Detector & Light Source Performance ........... 40 3.3.1 Substitution Method for Outside the Sphere Configuration.................................................. 41 3.3.2 Substitution Method for Inside the Sphere Measurements.................................................... 44 3.4 Angled Sample Holders ................................................................................................................. 45 3.5 Data Reduction............................................................................................................................... 47 3.5.1 Basic Data Reduction........................................................................................................... 47 3.5.2 Band-Integrated Values........................................................................................................ 50 3.5.3 Comparison of Surface Emittance and Absorptance from a Flame...................................... 51 4.0 Results & Discussion........................................................................................... 53 4.1 Comparison of Inside vs. Outside the Integrating Sphere Tests..................................................... 53 4.2 Data Sample Set ............................................................................................................................. 54 4.2.1 Determination of Data Subset to be used for Spectroscopic Analysis .................................. 57 4.2.3 Comparisons by Area Density: Normal Incidence ............................................................... 59 4.2.4 Comparisons by Area Density: Angular Data...................................................................... 66 4.2.5 Area Density Effects on Virgin KW: Stacked Samples vs. AFP............................................ 70 4.3 Final Dataset Used to Represent Spectral Behavior of KimWipes® ............................................. 73 ii 4.4 Spectral Radiative Properties ......................................................................................................... 74 4.4.1 Normal Incidence Light that is Transmitted Off-Axis: ‘Forward Scattering’....................... 75 4.4.2 Virgin KimWipes®: Normal Incidence................................................................................. 77 4.4.3 Virgin KimWipes®: Angular Effects .................................................................................... 78 4.4.4 Angular Dependency: The Effect of Pathlength on Radiative Properties ............................ 81 4.4.5 Heat-Treated KimWipes®: Normal Incidence ..................................................................... 85 4.4.6 Heat-Treated Samples: Angular Effects ............................................................................... 91 4.4.7 Spectral Changes in the Carbonyl Band............................................................................. 101 4.4.8 Void Spaces between Fibers and their Effect on the Radiative Property Values................ 103 4.4.9 Comparison of Heat-Treated Samples with Burned Sample............................................... 107 4.5 Band Integrated Data Results....................................................................................................... 110 4.5.1 Integration of Representative Data Set............................................................................... 110 4.5.2 Example of Band-Integrated Data...................................................................................... 111 4.5.3 Application of Kirchoff’s Law to Band-Integrated Properties ........................................... 115 4.5.4 Example Use of Band Integrated Data: Radiative Coupling.............................................. 117 4.5.5 Narrow Band (Imaging Space) Integrated Values.............................................................. 121 4.5.6 Estimation of Temperature Errors if Incorrect Emittance Values Used............................. 126 4.6 Determination of Activation Energy ...........................................................................................