Solar barrier performance of water mist cooling: Applications using nano- and microsized droplets and bubbles

•A mist cooling device is developed to block uncomfortable solar radiation.•Mist cooling without uncomfortable effects.•Radiative transfer analyses were conducted in a mist layer with a plate model.•The radiative properties of single-water droplets and bubbles are quantified.•It is shown that unwanted thermal radiation can be reflected with water particles. Many areas on earth have hot climates because of the high temperatures during summer and strong solar radiation. Water mist cooling is useful as an environmentally friendly urban system that can provide relief in these high-temperature conditions. To improve the utilization of the water mist cooling system, radiative transfer analysis was conducted to develop a mist cooling device that can block the uncomfortable solar radiation without causing discomfort because of the use of nano- and microsized droplets and bubbles. Herein, the radiative properties of single-water droplets and bubbles are calculated from a broad range of particle sizes and wavelengths. The extinction and scattering efficiencies of microscale droplets and bubbles are high in the solar spectral region, and they have the potential to reflect near infrared light. To model the radiative transfer in a water mist layer, a radiation analysis was conducted in a parallel plane model in one-dimension. The effects of particle size on spectral reflectance and total solar reflectance were discussed. The total solar reflectance is shown to increase with increasing particle sizes until it reaches its maximum value. It is demonstrated that undesirable thermal radiation can be reflected with the use of optimized water particles.