Passive and Dynamic Phase-Change-Based Radiative Cooling in Outdoor Weather

Abstract

Radiative cooling has attracted considerable attention due to its tremendous potential in exploiting the cold reservoir of deep sky. However, overcooling always occurs in the conventional static radiative coolers because they operate only in the cooling mode in both hot and cold. Therefore, a dynamic radiative cooler based on phase change materials is highly desired. Nevertheless, the practical outdoor phase-change-based dynamic radiative cooling has not yet been experimentally demonstrated. To satisfy the stringent requirement of the phase-change-based radiative cooler in outdoor weather conditions, we engineered the phase-change material (VO 2 ) to possess the room-temperature phase-transition capability for typical weather conditions. Second, the reconfigurable cavity consists of the lossless spacer to ensure the magnitude of thermal modulation and suppress the solar absorption simultaneously. Third, the practical selective-filtering method is devised to shield the solar irradiance while permitting the thermal emission. Our experiment demonstrates that these materials and photonic measures can work together to realize the dynamic radiative cooling in actual weather conditions, which shows a self-adaptive switch between the ON-cooling state in hot daytime and the OFF-cooling state in cold nighttime. The study pushes the radiative cooler toward multifunctionality and provides beneficial guidance for the phase-change-based intelligent thermal control.

Functional Radiative Cooling: Basic Concepts, Materials, and Best Practices in Measurements

“…The most commonly adopted material in adaptive RC is VO 2 , which undergoes an insulator-to-metal transition (IMT) at the temperature of T IMT = 68 °C. The transition temperature can be reduced to near room temperature by introducing dopants such as tungsten and chromium. ,− In a recent study, Tang et al developed a flexible temperature-adaptive RC device based on W-doped VO 2 . The device structure resembles a Fabry–Perot etalon consisting of an Ag reflector, a BaF 2 dielectric, and a lithographically patterned 2D array of W-doped VO 2 (Figure a) with a transition temperature of 22 °C.…”

Colloidal inorganic nano- and microparticles for passive daytime radiative cooling

“…By utilizing the tunable optical and thermal properties of VO 2 , various types of self-adaptive RCMs were designed for tunable thermal management, although most of them were fabricated by means of chamber-based thermal deposition of VO 2 layers [ 108 , 109 ]. Tang et al developed a temperature-adaptive radiative coating by using the strongly correlated electron material W x V 1-x O 2 , the transition temperature of which was tailored to ~ 22 °C (x = 1.5%) [ 104 ].…”

“…By utilizing the tunable optical and thermal properties of VO 2 , various types of self-adaptive RCMs were designed for tunable thermal management, although most of them were fabricated by means of chamber-based thermal deposition of VO 2 layers [108,109]. Tang et al…”

Dynamic modulation of thermal emission -- a Tutorial

“…On the other hand the areas which have undergone the complete phase cycle, from crystalline to amorphous and back from amorphous to crystalline are barely distinguishable from the crystalline substrate, highlighting the reversibility of the process. The second class includes materials which transition between a dielectric and metallic phase, as it is the case for vanadium dioxide (VO 2 ) 100,[112][113][114][115][116][117][118][119] . In this case, since the metal-insulator transition of VO 2 happens at about 340 K 120 , this material is often used for non-volatile phase transitions.…”