| As one of effective methods for cooling partial urban spaces,passive evaporation for cooling the horizontal or vertical urban surfaces,such as pavements,has been concerned a lot.For the most of urban road are made of asphalt,it is helpful a lot to study how passive evaporation for watering the asphalt road work.This paper studied watering for evaporation cooling,based on the energy-balance equation,on an open road at SCUT,Guangzhou,Guangdong Province.The result shows that cooling effect is made of several factors,and the evaporation rate during watering period has been estimated.Based on some ideal conditions,the factors contain longwave radiation,shortwave radiation,heat convection between road and air,and heat conduction from asphalt surface to deeper material.Another equation,based on the analysis on how water receive energy,shows that the effect of watering contains two points,containing heat conduction between liquid water and heat road,and latent heat.The two equations above are simultaneous to calculate evaporation rate.The experiment,mean to study how thermal parameters of the road surface change after watering,show that the influencing factors contain the first time of watering,watering rate,the way of watering,and water storage capacity.The best first time is 9:00 to 9:30 in July and 9:30 to 10:30 on Aug.and Sep.days.Albedo of road surface would reduce by 0.055 after watering.And it reduces by about 8.21? on surface,1.30? on the air at 1m height.Although it is no obvious different about SET* after watering,it can reduce building energy validly.The mothed of saving water has been argued.Average evaporation rate during watering time on open asphalt road in Guangzhou can reach to the value of 0.169mm/h ? ?0.179mm/h.And it most economical when watering rate reach evaporation rate.Purling and spraying are better way to cooling.Data also shows that heat taken from road by watering occupies 7.58% equally of all energy the road absorbs. |
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