Thermal Signature Management

ABSTRACT HALL, MICHAEL STEVEN. Thermal Signature Management. (Under the direction of Dr. Behnam Pourdeyhimi.) Thermal signature management takes the form of altering a material’s emissivity or modifying a surface’s temperature to influence the amount of energy radiated from its surface. For many applications and for this research the former type of thermal signature management is of primary focus. Emissivity is a value that represents how readily a material emits radiation when compared to a perfect emitter. Controlling a material’s radiative heat transfer offers the opportunity for thermal camouflage, better insulation properties, or better cooling properties depending on how emissivity is altered. Low emissivity coatings were created by applying a knife coating consisting of a polyurethane dispersion containing aluminum flakes onto woven polyester and tent fabric (PE/PET nonwoven with a TPO back coating) substrates. Coatings were created at a variety of wet weight percentages (5, 10, 20, 30%) with three Al flakes varieties that had median diameters of 9, 14, and 55 μm. Above those weight percentages some coatings experienced peeling issues. To measure emissivity a testing setup was constructed using a temperature controller, thermocouple, high emitting reference of known emissivity (black electrical tape), highly reflective reference (polished brass), heating pad, highly conductive copper plate, melamine foam, polycarbonate tube, FLIR t650sc Infrared Camera, FLIR Tools software, and a camera tripod. All particle size coatings experienced decreases in emissivity as particle weight percentage increased. The medium sized, 14 μm Al flakes achieved lower emissivities than all other particles sizes at every wet weight percentage, except at 5 %. Notably, 9 and 14 μm coatings were observed to start demonstrating blackout effects at wet weight percentages as low as 15 and 20 % for 14 and 9 μm coatings, respectively. The blackout effect being the blocking of all or the majority of visible light when a light source is placed near it. This finding indicates these coatings may have potential applications in areas that traditional blackout coatings are utilized in, such as military tents. Low emissivity coatings on the inner surface of a tent were noticed to advantageously reflect light back into a tent, instead of absorbing it like a blackout coating would, which reduces the energy needed to illuminate a tent. thermal model for steady state was developed by modeling the tent fabric system as a circuit to examine the effects of the coatings on the structure’s thermal resistance. Increases in thermal resistance were confirmed in the model. Overall low emissivity coatings on the inner surface of tent fabric were shown to aid in tent illumination back reflecting visible light back inwards, provided a blackout effect, and increase thermal resistance. Polyurethane coatings produced by a doctor blade with either 16 or 40 mil gap sizes were also shown to be capable of use in attaching LED fibers. © Copyright 2017 Michael Steven Hall All Rights Reserved Thermal Signature Management by Michael Steven Hall A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Textile Engineering Raleigh, North Carolina 2017 APPROVED BY: _______________________________ _______________________________ Dr. Behnam Pourdeyhimi Dr. Benoit Maze Committee Chair _______________________________ Dr. Hechmi Hamouda DEDICATION I would like to dedicate this to my wife, Melanie Martin; my parents, Steven and Beverly Hall; my close friends, Stefan Garcia and Tyler Lindley; my brother, Andrew Hall; faculty member, Dr. Jeffrey Joines; and to Steven Malaret whose love for family, friends, community and God act as a reminder of what is truly important in life. ii BIOGRAPHY Michael Hall was born in Raleigh, NC and was raised in nearby Clayton, NC. He graduated Magna Cum Laude and as a Scholar from North Carolina State University with a Bachelor’s of Science in Textile Engineering in 2015. In order to further his knowledge of Textiles and Nonwovens he decided to enroll in the Master’s of Science in Textile Engineering program at North Carolina State University in 2015. After graduation, he plans to pursue a career in product development. Outside of academics and work, he has been an active runner and has completed various half marathons and a marathon. iii ACKNOWLEDGMENTS Behnam Pourdeyhimi, Ph. D. Hechmi Hamouda, Ph. D. Benoit Maze, Ph. D. Head of Machine Shop: Hai Bui Officemates: Nguyên Khánh Vũ, Paula Cuervo, Farzad Rezaei, Mesbah Najafi Lab Managers/Technicians: William Barnes, Amy Minton, Eric Lawrence, Bruce Anderson In particularly, I would like to give a special acknowledgment to Dr. Behnam Pourdeyhimi for his guidance and patience with my research, for his graduate level course TT/NW 508 that furthered developed my interest in product development, and due to a chance meeting with him at a dinner in 2014 acting as a catalyst that eventually led to me pursuing a graduate education. Thus, I would like to give a special acknowledgement to my advisor, Dr. Behnam Pourdeyhimi since without his influence this thesis would have never been created. iv TABLE OF CONTENTS LIST OF TABLES .................................................................................................................. viii LIST OF FIGURES ................................................................................................................... ix I. Introduction ............................................................................................................................. 1 II. Literature Review ................................................................................................................... 3 A. Brief History of Camouflage ......................................................................................... 3 B. Types of Camouflage and Camouflage Spectrums ........................................................ 4 C. Thermal Infrared Radiation ........................................................................................... 7 D. Approaches for Creating Thermal Camouflage ........................................................... 18 i. Introduction ................................................................................................................ 18 ii. Adaptive Camouflage .............................................................................................. 20 iii. Temperature Regulation Approach .......................................................................... 21 iv. Low Emissivity Surface Approach .......................................................................... 25 E. Background on Military Coverings ............................................................................. 32 i. Introduction ................................................................................................................ 32 ii. Military Tents .......................................................................................................... 33 1. Current Designs ....................................................................................................... 33 2. Possible Future Designs........................................................................................... 37 3. Concluding Remarks ............................................................................................... 38 iii. Ultra Lightweight Camouflage Netting Systems (ULCANS) ................................... 39 F. Approaches to Low Emissivity Components ............................................................... 41 i. Introduction ................................................................................................................ 41 ii. Binders .................................................................................................................... 42 iii. Low Emissivity Components ................................................................................... 46 v iv. Other Potentially Useful Materials ........................................................................... 53 G. Production .................................................................................................................. 56 i. Overview .................................................................................................................... 56 ii. Knife Coating .......................................................................................................... 59 iii. Electrospinning ....................................................................................................... 63 H. Standards .................................................................................................................... 65 i. Tents ........................................................................................................................... 65 ii. ULCANS ................................................................................................................ 66 iii. Thermal Measurements and Emissivity ................................................................... 69 I. Concluding Remarks ...................................................................................................... 72 III. Materials ............................................................................................................................. 73 IV. Emissivity Testing Setup ....................................................................................................

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