Experimental and simulation studies on enhancing passive radiative cooling of stratospheric airship envelopes with microporous polymer film

The stratospheric airship is very sensitive to external temperature variations. Temperature changes in the airship envelope and internal gases caused by diurnal variations in external solar radiation will result in changes in the shape and buoyancy of the airship. The traditional thermal control methods are limited in their thermal control effect and usually involve additional weight or energy costs. Passive daytime radiative cooling (PDRC) is an effective strategy for achieving cooling in energy-limited systems and is expected to solve the challenges of thermal control of airships. In this study, a multilayer structure of PDRC material consisting of a microporous polytetrafluoroethylene (PTFE) film on the top of the envelope was designed to increase the reflectance at visible wavelength and the emissivity in the atmospheric window. The PDRC envelope achieves a remarkable solar reflectance of 96.1% and an atmospheric transparency window emissivity of 93%. The airbag models are fabricated to test the ground cooling performance, and the results indicated that the PDRC envelope material achieved a significant temperature reduction of about 6 °C compared to the control group under solar intensity of ∼1100 W/m2. Moreover, the cooling performance of stratospheric balloons and airships at high altitude with PDRC envelopes applied was verified by FLUENT thermal simulations. In summary, this work presents a simple and scalable hot-pressing method to fabricate PDRC envelope materials, which not only effectively solves the thermal control problem of stratospheric airships, but also will provide a new application of PDRC materials.