ABSTRACT WEINER, NATHAN CHRISTOPHER. Flexible Peltier Coolers for Thermal Comfort and Bedding Applications
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ABSTRACT WEINER, NATHAN CHRISTOPHER. Flexible Peltier Coolers for Thermal Comfort and Bedding Applications. (Under the direction of Dr. Jesse Jur). The thermal comfort of a mattress and bedding system is critical to obtaining a quality night sleep. There is a growing trend in the mattress industry to employ new materials which create a cooling effect for sleepers with the use of innovative phase change materials (PCMs) or cooling gels included in the near-surface foam constructions of a mattress. These mattresses seek to alleviate overheating during sleep or provide a more comfortable environment for those who may suffer from medical conditions which cause excess heat production. However, these materials are passive coolers which do not allow for precise, customized control of the bedding microclimate and often provide minimal difference in comfort after the initial period of a human’s sleep cycle. The goal of this work is to develop a novel active cooling technology which could be used in a mattress pad and/or comfort layer. Peltier coolers, or thermoelectric coolers (TECs), provide a unique solution for active cooling as they are solid-state heat pumps with the ability for precise temperature control. TECs are typically light-weight and lack a refrigerant which makes them an ideal alternative to traditional cooling systems. Over the course of this research, early prototypes using thermoelectric (TE) elements, conductive patterning/ printing processes, and various polymer materials have been studied. These devices are evaluated for both cooling and mechanical performance for their potential use in mattress applications. The knowledge from this research and the fabrication processes developed serve as a groundwork for future constructions of more efficient large-area, flexible cooling systems. This work also provides insight into the mechanisms that drive Peltier cooling, including the important requirements of the heat flow and dissipation of such a system. The ultimate outcome of this work is a foundation upon which modeling of novel TEC device constructions are evaluated as compared to bench-top designs, along with factors in scaling this technology for broad use in textile products. © Copyright 2017 Nathan Christopher Weiner All Rights Reserved Flexible Peltier Coolers for Thermal Comfort and Bedding Applications by Nathan Christopher Weiner 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. Jesse S. Jur Dr. Russell E. Gorga Committee Chair _______________________________ Dr. Mehmet Ozturk BIOGRAPHY Nate Weiner was born and raised in Rochester, NY where he attended Penfield High School until graduating in 2011. He decided to move to Raleigh, NC to attend NC State University with plans to pursue a career in materials development for athletic apparel or biomedical textiles. He earned Bachelors’ degrees in Textile and Biomedical Engineering with concentrations in product engineering and biomaterials and graduated summa cum laude in 2016. During his summers, he learned to apply his studies through four separate internships at Luna Innovations, Freudenberg Nonwovens, Nike Inc., and Eastman Chemical Company. While in school, Nate was involved with the club tennis team all 5 years and lead the team as president for 3 of them. He was also an Engineering Ambassador during his third and fourth years serving as a teaching assistant and mentor for students in the introductory engineering course. In his final year as an undergrad, Nate was accepted into the Accelerated Bachelors/Masters program within the Textile Engineering program. He joined the Nano- extended Textiles (NEXT) Research Group as a Master’s student in August 2016 under the direction of Dr. Jesse Jur. His research focused on developing methods for producing flexible thermoelectric coolers (TECs) to be used in bedding and personal cooling applications. Nate will graduate in December 2017 with a Master of Science in Textile Engineering and plans to pursue a career with an athletic, outdoor, or wearable technology company. ii ACKNOWLEDGMENTS I would like to thank my research advisor Dr. Jesse Jur for his guidance and encouragement during this project as well as his financial support during my time as a researcher in the NEXT lab. This project and the following research efforts were sponsored by Serta Simmons Bedding Company who have provided a great deal of experience as well as funding for the project. I want to thank Michael DeFranks and Brian Anderson at SSB for their help and feedback throughout our research developments as well as the other members of the SSB team working to support this project. Additional research efforts were also conducted by Dr. Mark Losego’s group at Georgia Tech so I would like to thank him and his team as well. I would also like to thank Emiel DenHartog and Sophie Guevel in the TPACC lab at the College of Textiles for taking the time to provide their advice and assistance in the use of their testing facilities. Furthermore, I want to acknowledge and thank my committee members Dr. Russel Gorga and Dr. Mehmet Ozturk for serving on my committee and providing direction when necessary. Finally, I want to express my sincere gratitude to my fellow researchers and friends in the NEXT research lab: Allison Bowles, Amanda Myers, Ben Gillespie, Braden Li, Cemile Aksu, Hasan Shahariar, Inhwan Kim, Jack Twiddy, Lanjun Yin, Raj Bhakta, and Wade Ingram. I am incredibly grateful for their support, encouragement, and ideas throughout this journey. iii TABLE OF CONTENTS LIST OF TABLES ................................................................................................................... vi LIST OF FIGURES ............................................................................................................... viii CHAPTER 1: Sleep, Mattress Construction, and Mattress Comfort ........................................ 1 1.1 Introduction ................................................................................................................ 1 1.2 Sleep ........................................................................................................................... 1 1.3 Mattress Comfort........................................................................................................ 3 1.3.1 Mattress Properties.............................................................................................. 3 1.3.2 Mattress Core Materials ...................................................................................... 7 1.3.2.1 PU Foams .................................................................................................... 9 1.3.2.2 Latex Foams .............................................................................................. 10 1.3.2.3 Innerspring Cores ...................................................................................... 11 1.3.2.4 Fluid-based Beds ....................................................................................... 13 1.3.2.5 Natural cores .............................................................................................. 14 1.3.3 Comfort Layer Materials................................................................................... 15 1.4 Potential Impact of a Thermoregulating Mattress on Sleep ..................................... 17 1.4.1 Sleep from a Thermoregulatory Perspective ..................................................... 17 1.4.2 Sleep Promotion ................................................................................................ 22 1.5 Impact of Mattress Design on Sleep ........................................................................ 27 CHAPTER 2: Thermoelectric Fundamentals and Cooling ..................................................... 36 2.1 TE Fundamentals...................................................................................................... 36 2.1.1 Seebeck Effect .................................................................................................. 37 2.1.2 Peltier Effect ..................................................................................................... 38 2.1.3 Thomson Effect ................................................................................................. 38 2.2 Figure of Merit ......................................................................................................... 39 2.3 COP .......................................................................................................................... 42 2.4 Peltier Cooling Devices ............................................................................................ 45 2.4.1 Applications of Peltier Coolers ......................................................................... 46 2.5 Current Advances in Flexible TECs and TEGs ....................................................... 47 CHAPTER 3: State-of-the-Art Active Cooling Technologies ................................................ 51 3.1 Introduction .............................................................................................................. 51 iv 3.2 Personal Cooling ...................................................................................................... 52 3.3 Commercial TE Personal Cooling Products............................................................