Outdoor Thermal Management By Nanophotonic Structures

Outdoor thermal management is the management of the temperature of outdoor objects by controlling the heat transfer between the objects and the ambient.Due to climate change and the unnecessary energy waste on air conditioning systems,passive outdoor thermal management has become a hot topic with its advantages in low energy consumption and superior temperature regulation ability.Passive outdoor thermal management,including passive heating and cooling,is achieved by utilizing renewable outdoor resources such as the sun and the universe.Common materials for passive outdoor thermal management include paints,metals,polymers,and nanophotonic structures.Among them,nanophotonic structure has its outstanding advantages such as its ultra-thin thickness and flexibility of multispectral optical properties modulation,which make it a suitable candidate for realizing cost-effective outdoor thermal management.Although recent years have witnessed a surge of the study on outdoor thermal management,most of them are focused on single thermal function or single band optical property modulation.The work on multi-spectral and multi-functional thermal management is still lacking.Particularly,two challenges remain to be tackled:(1)Thermal management in extreme hot/cold environment;(2)Simultaneous management of the color.This thesis is focused on overcoming these two challenges via nanophotonic approaches.Meanwhile,a comprehensive study into the physical mechanism,device fabrication,and potential applications of multispectral thermal management is demonstrated:(1)In terms of outdoor personal warming with simultaneous color management,an ultrathin colored textile(?16 ?m)which maintains high sunlight absorptivity and low thermal emissivity is demonstrated.The textile is fabricated by depositing broadband solar absorbing gold/germanium coatings onto nanoporous polyethylene.It solves two major problems that conventional radiative thermal management was faced:1.Hight sunlight reflectivity in outdoor spaces;2.The dyeing process increases the outer surface emissivity.The indoor thermal measurement result shows that the personal warming ability of the colored textile is comparable to 6 mm-thick-sweatshirt.In outdoor thermal measurement,it is demonstrated that the skin simulator covered by the ultrathin colored textile witnesses a temperature increase of 6.3? compared to a 2 mm-thick-sweatshirt.Moreover,the colored textile maintains excellent wearability,including windproof,water vapor permeability,and wettability.This colored textile has potential applications in the field such as personal protective clothing and multispectral camouflage.(2)In terms of protecting individuals from both extreme hot and cold weather,a cheap and dual-functional textile is demonstrated.Based on asymmetrically engineered optical properties at each side,the textile is able to achieve both outdoor personal heating and cooling.Its heating mode is achived by selective solar absorbing coating of Cu-Zn nanoparticles,which manifests high sunlight absorptivity(>0.8)as well as low thermal emissivity(?0.16).During the heating mode,the textile is able to increase the skin simulator temperature by 8.1? compared to a 1 mm-thick-black sweatshirt.The cooling mode of the textile is achieved by porous PMMA coated expanded PTFE and aluminum film,which has high sunlight difffuse reflectivity(?0.91)and high thermal emissivity(?0.87).During the cooling mode,the textile can decrease the skin simulator's temperature by 6.3? compared to a 0.5 mm-thick-white sweatshirt.Based on its superior localized temperature regulation ability,we combined the dual-functional textile with a commercial thermoelectric generator to realize all-day thermoelectricity generation.The resulting dual-functional textile is cheap,easy-to-manufacture,and wearable.It thereby provides a suitable strategy for outdoor personal thermal management and pervasive electricity generation.(3)Regarding color-preserving radiative cooling of air-conditioned room,a scalable optically transparent(>0.8)but thermal radiation reflective(>0.8)Low-E film and an optically transparent(>0.8),near-infrared reflective(>0.9),thermal radiation emissive(>0.8)structure are demonstrated.The indoor test reveals that by using the Low-E film,the air-conditioned room temperature witnesses a decrease of 6? when the absorbed solar power density is 1000 W m-2.Moreover,the radiative cooling power density of the outer surface can also be increased by 20 W m-2.This nanophotonic device is promising to reduce the unnecessary energy consumption on room temperature regulation,and it is well suitable for scalable fabrication since it involves only film deposition.To recapitulate,this thesis makes a comprehensive study into outdoor thermal management,which develops a series of nanophotonic structures for different thermal functions.The study is focused on simultaneously modulating multiband optical properties of the nanophotonics structures for on-demand color-preserving personal heating,cost-effective personal heating and cooling,and the radiative cooling efficiency enhancement for actively cooled chambers.The proposed strategies in this thesis will provide a deep insight into the feasibility of multiband optical property engineering with nanophotonic structures.Moreover,they also show great potentials in applications such as localized temperature modulation,energy saving for buildings and cars,and multiband camouflage.