Radiative Cooling Nanofabric for Personal Thermal Management

Abstract

A wearable textile that is engineered to reflect incoming sunlight and allow the transmission of mid-infrared radiation simultaneously would have a great impact on the human body’s thermal regulation in an outdoor environment. However, developing such a textile is a tough challenge. Using nanoparticle-doped polymer (zinc oxide and polyethylene) materials and electrospinning technology, we have developed a nanofabric with the desired optical properties and good applicability. The nanofabric offers a cool fibrous structure with outstanding solar reflectivity (91%) and mid-infrared transmissivity (81%). In an outdoor field test under exposure of direct sunlight, the nanofabric was demonstrated to reduce the simulated skin temperature by 9 °C when compared to skin covered by a cotton textile. A heat-transfer model is also established to numerically assess the cooling performance of the nanofabric as a function of various climate factors, including solar intensity, ambient air temperature, atmospheric emission, wind speed, and parasitic heat loss rate. The results indicate that the nanofabric can completely release the human body from unwanted heat stress in most conditions, providing an additional cooling effect as well as demonstrating worldwide feasibility. Even in some extreme conditions, the nanofabric can also reduce the human body’s cooling demand compared with traditional cotton textile, proving this material as a feasible solution for better thermoregulation of the human body. The facile fabrication of such textiles paves the way for the mass adoption of energy-free personal cooling technology in daily life, which meets the growing demand for healthcare, climate change, and sustainability.

Strain-adjustable reflectivity of polyurethane nanofiber membrane for thermal management applications

“…The Es-TPU-0% exhibited good cooling performance with a 10 °C drop in temperature under a solar intensity (Isolar) of 900 W m -2 at 12:00-13:00. After 15:00, the decreased irradiance accompanied by the increased relative humidity resulted in a weakened cooling capacity [64]. The cooling performance of the Es-TPU membrane is attributed to its high solar reflectivity (reducing heat gains) and high infrared emissivity (increasing radiative losses).…”

Recent progress in organic-based radiative cooling materials: fabrication methods and thermal management properties

“…also closely affect the cooling power of materials. 46 As shown in schematic diagram (Fig. 1) 47 the net radiative cooling power (P net ) of the material mainly depends on the thermal outward radiative power by the cooler (P rad ), while the heat absorption comes from three parts (P abs ): absorbed incident solar radiation (P sol ), absorbed energy from atmospheric thermal radiation (P atm ), heat conduction-convection from ambient radiation (P cond+conv ).…”

Colloidal inorganic nano- and microparticles for passive daytime radiative cooling

“…Wide-bandgap semiconductors such as TiO 2 and ZnO offer considerable advantages as solar reflectors in RCMs because these NPs and MPs are commercially available, inexpensive, and exhibit high reflectance in the visible and NIR regions owing to their high refractive indices [ 23 , 70 , 71 ]. However, their absorption properties in the UV region reduce the RC efficiency because there is a non-negligible portion of UV in the solar spectrum, and the absorption of UV energy increases the temperature of the RCMs.…”

“…Radiative cooling (RC) has recently attracted significant attention as a promising temperature-lowering strategy that does not require external energy for cooling [4][5][6][7][8]. RC materials (RCMs) have great potential for use in various applications, such as energy-saving buildings [9][10][11][12][13], vehicles [14][15][16], water harvesting [17,18], solar cells [19,20], and personal thermal management [21][22][23]. RCMs spontaneously reduce the temperature of a system by releasing thermal energy into the cold sink of outer space through infrared (IR) radiation [6,24,25].…”