Abstract:

Significance With the aggravation of global warming and the depletion of fossil energy, efficient regulation of environment temperature with low energy consumption has become an important issue to be solved urgently. As a passive cooling method without external energy consumption, radiation refrigeration technology has attracted extensive attention, and has made remarkable research progress in many fields such as building cooling, photovoltaic device cooling and personal thermal management, thus becomes a hot research topic. Based on fiber materials, the designs of structure and components with radiation refrigeration function are reviewed, which not only effectively improve the cooling effect, but also provide a more feasible path for the practical application of radiation refrigeration technology in the field of personal thermal management(PTM).

Progress In recent years, substantial progress has been made in the research of radiation refrigeration nanofiber membranes. Radiation refrigeration fiber materials mainly include infrared radiation polymers (such as PVDF, PMMA, cellulose, etc.) and infrared radiation polymers combined with inorganic materials (such as TiO₂, SiO₂, Al₂O₃, etc.). The size distribution of electrospun nanofibers is consistent with the solar wavelength, which induces Mie scattering effect and enhances the solar reflectivity of the film. However, the polymer has a specific chemical structure, and the mid-infrared (MIR) emissivity of the film at the wavelength of 8-13 μm is achieved by molecular bond vibration and stretching. Among polymer-based membranes, polyethylene oxide (PEO) nanofiber membranes are composed of random nanofibers with disordered molecular chains. Compared with non-selective emitters, the cooled temperature at night is increased at about 3 ℃, and it is cooled at 5 ℃ under the sun irradiation. If inorganic materials are compounded with the polymers, the radiation refrigeration effect is further improved, but the wearing comfort of textiles may be greatly reduced. The average reflectivity of PMMA/SiO₂ porous fibers and composite porous films in the solar spectrum band is 97%, the emissivity in the atmospheric window band is over 90%, and the temperature can be reduced by over 5 ℃ during the day. Coaxial electrospinning can effectively overcome the limitations of poor mechanical properties of traditional electrospun fibers by endowing the fiber with a core-sheath structure. Poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) and tetraethyl orthosilicate (TEOS) are used as composite shells, and octadecane is encapsulated as the core phase change material. The solar reflectivity is 95.0%, and the emissivity is 88.6% under their radiation of 550.2 W/m².

Conclusion and Prospect Radiation refrigeration technology is used to prepare fiber membrane through electrospinning, the products from which, demonstrating good cooling effect, have been applied in personal thermal management. Although the electrospun nanofiber membrane based on radiation refrigeration has made remarkable progress in experimental research, its transformation from laboratory results to large-scale industrialization still faces many technical bottlenecks and practical challenges. At present, there are still some problems in the preparation of related materials, such as difficulty in industrial production, low production efficiency, high preparation cost and unsatisfactory durability of materials. In addition, the research is still limited on dynamically adjusted textiles, color radiant refrigeration textiles and multifunctional integrated radiant refrigeration textiles to meet the needs of different groups of people. In the future, the research needs to be further deepened from the aspects of material molecular structure design, spinning process optimization and composite interface regulation, and develop radiation refrigeration fiber products with high performance and wearability to promote its large-scale application in the field of personal thermal management. At the same time, the use of such materials is expected to extend to multiple scenarios such as building energy saving, special clothing, glacier protection, aerospace, automobile interior, cold chain logistics and agricultural greenhouse, leading to acceleration of the all-round popularization and industrialization of radiation refrigeration technology in the living environment.

Key words: radiation refrigeration, electrospinning, nanofiber membrane, personal thermal management, spectral regulation