Research On Evaporation Cooling Mechanism Of Water-retaining Semi-flexible Pavement

The high temperature of urban road pavement is an important factor that aggravates the urban heat island effect,and it is also the main "culprit" of road damage and reduced road service life.The water-retaining semi-flexible pavement has good water-retaining and cooling performance and road performance,and the construction is simple and easy to operate.Reducing the temperature of the road surface and the ground near the ground through water absorption evaporation is an effective measure to alleviate the urban heat island effect.It is both environmentally friendly and economical.If such a pavement is paved in a large area,it will greatly alleviate the "heat island effect" of the city,improve the ecological structure,and optimize the living environment.First,on the basis of analyzing the control equations of multiple porous media thermal-mass coupling models,the conservation model of each phase in the porous media is selected as the analytical model of the water-retaining semi-flexible pavement to establish the control equations.Based on the basic principles of heat transfer,experimental correlations,and heat and mass transfer comparisons,the calculation formulas for the heat flux density and water evaporation of the water-retaining semi-flexible pavement boundary were established.Using multiple heat and mass coupling theories,only atmospheric temperature and air Humidity,wind speed,solar radiation and other meteorological elements and material parameters are estimated to predict the temperature,moisture,water vapor and evaporation of water-retaining semi-flexible pavement.The finite element software COMSOL MULTIPHICS was used to numerically simulate the temperature of the asphalt concrete pavement under natural convection and the temperature,moisture and water vapor concentration of the semi-flexible pavement,and the temperature analysis model and water retention of the asphalt concrete pavement were verified through indoor tests Evaporative cooling model of semi-flexible pavement.The results show that compared with asphalt pavement,the water-retaining semi-flexible pavement heats up more slowly,the surface temperature is lower,and the top surface temperature rises faster than the bottom surface.After radiation stops,the surface temperature drops faster than the bottom surface temperature due to the high temperature evaporation of the pavement In the process of temperature increase,a high concentration area of ??water vapor will be formed near the top surface,while in the process of temperature decrease,a high concentration area will be formed at the bottom.Afterwards,the radiation time was extended to 9 hours,and the evaporation cooling effect under different radiation absorption rates was analyzed,and it was found that the evaporation amount was significantly different before and after the surface was dried.It is regarded as the duration of cooling before drying.The lower the radiation absorption rate,the smaller the surface evaporation,the smaller the cooling range,and the longer the evaporative cooling duration.Secondly,the effect of evaporation cooling under the conditions of extreme radiation forced convection and different wind speeds is studied.The results show that due to the influence of wind speed,a high concentration of water vapor is formed in the upper middle layer of the pavement,and the water evaporation rate at the air inlet is faster than the air outlet The temperature of the air outlet is far higher than the temperature of the air outlet;under the same air humidity,the greater the wind speed,the faster the water evaporation rate,the greater the surface evaporation,the greater the temperature reduction,the faster the surface drying,the greater the temperature difference between the air inlet and air outlet,but the temperature is lower The shorter the duration.Finally,study its evaporation cooling effect under extreme radiation forced convection under different air humidity conditions,and further analyze the near-surface air temperature under different air humidity,introduce the concept of human comfort in meteorology,and use three different comforts The mathematical model of degree evaluation comprehensively evaluates the human comfort level of the semi-flexible pavement near the ground space.The results show that under the same wind speed,the higher the air humidity,the slower the water evaporation rate,the higher the surface temperature,the smaller the cooling range,but the longer the cooling duration;the air temperature at the air inlet of the near-ground space above is lower than the air outlet The temperature and air temperature decrease with increasing distance from the road surface,and the same as the atmospheric temperature at 2.5m above,and the three comfort evaluation indexes at the height of 1.5m-2.0m above show that they are more comfortable.The thermal environment feels comfortable.