Study On Evaporative Cooling Characteristics Of Pervious Pavements In Hot And Humid Areas

The imperviousness of the underlying surface of cities is one of the main reasons,causing the urban heat island phenomenon.As a new type of artificial pavement,pervious pavement could not only permeate water but also store a certain of water inside the surface layer and use water evaporation to remove the accumulated heat,thus reducing pavement surface temperature.However,the evaporative cooling effect of pervious pavements is significantly affected by the thermal performance of pervious paving materials and usually neglected by most manufacturers in China,which brings great obstacles for promoting this technique to mitigate the urban heat island.To solve this problem,this thesis carried out the following work:1)Assessment of water absorption and retention performance of pervious paving materials.Based on extensive research on manufactures of pervious paving materials in hot and humid areas of China,five typical pervious paving materials were selected.Referring to international and domestic testing standards,the database and assessment method of water absorption and retention performance of typical pervious paving materials were established.2)Differences in evaporative cooling effect of various pervious paving materials.Based on the hot and humid climate wind tunnel experiment,this thesis revealed the influence of hygrothermal properties of pervious paving materials on its evaporative cooling performance.Comparing with the saturated volume water content,the higher capillary water absorption rate was the key parameter to maintain the lower surface temperature of pervious paving materials;the contribution of high reflectivity to surface temperature drop was weaker than that of evaporation.The uneven energy consumption at different stages of evaporation was the main reason.3)Evaporation model of typical pervious paving materials.Based on typical summer meteorological day of Guangzhou,a representative city in hot and humid region,this thesis established a regression equation for estimating the cumulative evaporation of three typical pervious paving materials;furthermore,referring to the evaporation calculation method by using evaporation resistance in the research field of soil science,the regression equations between the volumetric water content and the evaporation resistance of three typical paving materials were obtained.4)Influence of evaporative cooling effect of typical pervious pavements.Through outdoor sample experiment of typical pervious pavements in Guangzhou,this thesis explored the effects of different types of pervious pavements on outdoor thermal environment(surface temperature,nearby air temperature and relative humidity,and thermal indicators WBGT and THI).Furthermore,one-dimensional unsteady heat transfer model of pervious pavement was established and the accuracy of evaporative resistance equations were examined by using this model and the influence of different watering start time on surface temperature change law was discussed.For the first time,this study established a pre-evaluation system for estimating the evaporative cooling effect of pervious paving materials based on water absorption,retention and reflectivity properties,built an accumulated evaporation database,regressed and validated the regressed evaporation resistance equations to calculate the evaporation rate,explored the reasonable water start point of pervious pavement to maintain the evaporative cooling effect.This study provided a significant reference and method to utilize pervious pavements to improve the quality of outdoor thermal environment.