EXPERIMENTAL STUDY ON HEAT TRANSFER ON AND UNDER GROUND CONSIDERED MOISTURE MOVEMENT

通过两年的时间对地面垂直温度分布和地表热流进行了长期观测。地面覆盖着五种不同的材料：裸土、草坪、混凝土路面、沥青路面和透水性沥青路面。长期观测结果表明，夏季混凝土路面和沥青路面的日平均表面温度均在40ﾟC以上。同一季节裸土和草坪的日平均地表温度比混凝土路面和沥青路面低7~10ﾟC。裸土和草坪80 cm处的地下温度全年都比混凝土路面和沥青路面低3~5ﾟ℃。由于水分蒸发…的抑制，混凝土和沥青路面下的土壤含水率较高根据土壤含水率的变化，测量了土壤的导热系数、体积比热和电阻。土壤在潮湿条件下的导热系数是在干燥条件下的两倍，为了预测土壤的热性能，对两种模拟模型进行了检验。一种是精确地考虑地下水分运动，另一种是简单地考虑地表水分蒸发的影响。在以前的模拟模型中，称为模型A，土壤中的水分根据含水率的梯度移动，土壤的热物性也随着含水率的变化而变化。后一种模型被称为模型B，它使用蒸发率来计算地表的蒸发量，并且热物性是恒定的。实测值与计算值的比较表明，模型A比模型B更能准确地反映地面和地下的重现换热现象。然而，模型B有足够的精度来预测地面和地下的热传递。较少

Long-term Observation of vertical temperature distribution and surface heat flux of the ground has been carried out through two years. The ground is covered with five different kind of materials; bare soil, lawn, concrete pavement, asphalt pavement and permeable asphalt pavement. The Observation includes the data acquisition of weather and water content of soil.The results of the long-term Observation show the daily average surface temperatures of the the concrete and the asphalt pavement are over 40ﾟC in summer. The daily average surface temperatures of the bare soil and the lawn are lower than those of the concrete and the asphalt pavement by from 7 to 10ﾟC in the same season. The underground temperatures of the bare soil and the lawn at the depth of 80cm are always lower than those of the concrete and the asphalt pavement by from 3 to 5ﾟC through a year. The water content of the soil under the concrete and the asphalt pavement is high because of the suppression of water evaporation … More at the surface.The thermal conductivity, volumetric specific heat and electric resistance of the soil were measured according to the variation of the water content. The thermal conductivity of the soil under wet condition has as two times large value as that under dry condition.Two types of simulation model are examined to predict the thermal performance of the ground. One exactly considers the moisture movement in the ground, and the other simply takes the effect of water evaporation at the surface into consideration. In the former simulation model, called Model A, moisture in the ground moves according to the gradient of water content and thermal properties of the soil also vary according to the water content. The latter model, called Model B, uses evaporation ratio to calculate the water evaporation at the surface and thermal properties are constant. The comparison of the measured and the calculated values shows Model A is more accurate than Model B in the viewpoint of the reproducing heat transfer phenomenon on and under the ground. Model B, however, has enough accuracy to predict the heat transfer on and under the ground. Less