Study Of Surface Temperature And Near-Surface Thermal Environment Of Different Pavements

With the accelerated global urbanization and the rapid growth of urban population,the urban thermal environment has deteriorated dramatically,forming the urban heat island effect(UHI),which affects human thermal comfort,endangers human health,and increases urban energy consumption.The urban thermal environment is closely related to the subsurface.The physical properties of the subsurface affect the pavement surface temperature and the distribution of radiant energy at the pavement surface,and change the ground-air heat exchange process,thus changing the near-surface thermal environment.Therefore,it’s urgent to study the interaction of the pavementnear-surface thermal environment system,reveal the law of the thermal material parameters of the subsurface and the meteorological synergy affecting the surface temperature and the near-surface temperature,and provide a theoretical basis for the scientific regulation of controllable parameters to reduce the surface temperature of different pavements.By combining theoretical analysis,experimental test and numerical simulation(COMSOL Multiphysics),this paper analyzes the influence of reflectivity on pavement temperature and near-surface atmospheric temperature.The following main conclusions were obtained:(1)For the study of controllable parameters of surface temperature,a pavement temperature calculation model is derived based on the road system heat transfer following a semi-infinite body one-dimensional transient heat transfer model.The controllability analysis reveals that the controllable thermal material parameter of the surface temperature is the reflectivity.Through the outdoor measurement test,the difference of surface temperature of different pavements is revealed,and the influence law of reflectivity and solar radiation on surface temperature is initially explored,which confirms the effectiveness of the controllable thermal material parameter for cooling.By combining the measured meteorological data with numerical simulations,the heat flow boundary model of pavement-near-surface thermal environment is established,and the simulated surface temperature is in good agreement with the theoretical calculated value,which verifies the accuracy of the model.(2)To address the distribution of near-surface air temperature,four types of pavement-near-surface atmospheric calculation models were established.It is found that the distribution of near-ground air temperature above pavements during daytime can be divided into three types: at sunrise,at noon,and at dusk.In each period,the temperature in the height range of 0～50cm above the grassland pavement fluctuated greatly,showing a trend of rising first and then falling;The temperature in the range of 0～50cm above cement and asphalt pavement decreases with the increase of height at sunrise and noon,and increases with the increase of height at dusk.The temperature in the range of0～100cm above the football field increases with the increase of height at sunrise,and decreases with the increase of height at noon and dusk.(3)To address the problem of the effect of reflectivity on near-surface air temperature at different heights,the reflectivity of the model was parametrically scanned from 0.1 to 0.5.The results show that the effect of pavement reflectivity on near-surface air is weakened with increasing height,and for both asphalt and concrete pavements,the effect height is 1m on sunny days and about 0.5m on rainy days.The difference caused by reflectivity on the average daytime temperature is greater than the average daily temperature,and has almost no effect on the average nighttime temperature.(4)To address the problem of how reflectivity affects the near-surface thermal environment in an urban canyon,an experimental study of the thermal properties of an urban model with different paved surfaces was conducted.It is found that for an urban street near the Tropic of Cancer,the hottest place is EW street,followed by the intersection and finally SN street.Increasing the reflectivity of the pavement in urban canyons can reflectivity cool the pavement(about 5-10 °C).