Integrated impacts of water mist spray and aspect ratios on thermal environment inside 2D street canyons: Scaled outdoor experiments

Water mist spray is promising to summer cooling in urban streets via evaporative cooling. However, there is still a lack of high-quality measurement dataset with high spatiotemporal resolution. The synergistic effects of water mist spray, building morphology, urban turbulence, and radiation processes on thermal environment remain unclear. Thus, by utilizing innovative scaled outdoor experiments under realistic atmospheric conditions with radiation processes, this paper investigates cooling performance of water mist spray under 50 and 100 ml/min water flow rate(WFR) inside two-dimensional street canyons with different aspect ratios (building height/street width, H/W = 0.5, 1, 2, H = 1.2 m) under calm weather condition. Hourly air temperature measurements in the central vertical plane of the water mist spray were recorded from 09:00 to 18:00. Results show that water mist spray has the best cooling performance inside the narrowest street canyon (H/W = 2), experiencing the maximum air temperature reduction of 10.7 °C with background air temperature of 30.6 °C under WFR=100 ml/min and highest relative humidity increase during the whole measurement period. The wider streets (H/W = 0.5, 1) attain smaller cooling intensities because the water vapor is less effective in filling the larger canyon space, resulting in poorer cooling performance. Although more researches are still required before providing urban design guidelines for water mist spray application, this paper is the first attempt to carry out high-quality scaled outdoor experiments to verify the impacts of urban water-mist cooling under realistic atmospheric conditions, which can provide high-quality validation datasets for numerical simulations.