Experimental Study on Evaporation in a Bare Land

裸地蒸发实验研究

• 批准号: 59550341
• 负责人: TOMOSUGI Kunio
• 金额: $ 0.83万
• 依托单位: Kyoto University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1984
• 资助国家: 日本
• 起止时间: 1984 至 1985
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-59550341/
• 关键词: Evaporation; Bare Land; Wind Tunnel; 地下水面; 水蒸気輸送

In order to clarify the evaporation process in a bare land affected by a meteorological and a land conditions in a complicated manner, a laboratory experiment was undertaken by continuously applying the airflow of a constant speed, temperature and humidity through a wind tunnel for a long time on a uniform porous material layer (pML) with unrestricted water table downwards. The PML was initially saturated. The employed porous materials are two kinds of sand (mean particle-diameter (d); 0.24 mm, 0.45 mm), the Akadama-soil (d = 3 mm) with a double structure of pores, macropore and micropore, and a uniform glass bead (d = 12 mm). Only the speed was variously changed for the condition of airflow. The following has been elucidated through the experiment. 1) The evaporation rate and the falling speed of eater table at the relatively early stage become large as the wind becomes strong and the pore-size of PML becomes small. However, the effect of wind speed on such quantites becomes very small with time except in the case of glass bead with large pores. 2) The evaporation rate divided by the friction velocity, when the water table is relatively high, is uniquely determined against the depth of water table. 3) The water content profile in the unsaturated zone above the water table can be approximated by the boundary drying soil-water retention curve except in a very dry place. 4) The evaporating front moves downwards from the surface of PML with time. 5) The water vapour in the PML above the evaporating front is transported by the molecular diffusion and by the turbulent diffusion. The movement near the surface of PML is mainly caused by the latter. The mixing length in the case of glass bead is a half magnitude of the particle-diameter.

为了阐明裸地蒸发过程受气象条件和地面条件的复杂影响，通过风洞长期连续施加恒速、恒温、恒湿的气流，在地下水位不受限制的均匀多孔材料层(PML)上进行了室内实验。PML最初是饱和的。所采用的多孔材料为两种沙子(平均粒径分别为0.24 mm和0.45 mm)、具有孔、大、微孔双重结构的赤潮土(d=3 mm)和均匀的玻璃微珠(d=12 mm)。只是速度随着气流状况的不同而有所不同。通过实验阐明了以下几点。1)PML相对早期的蒸发速率和下落速度随着风力的增强和孔径的减小而增大。然而，风速对这些量值的影响随着时间的推移变得非常小，除了具有大气孔的玻璃微珠的情况。2)当地下水位较高时，蒸发率除以摩擦速度相对于地下水位的深度是唯一确定的。3)除极干旱地区外，地下水位以上非饱和带的含水率分布均可用边界干化土壤水分保持曲线来近似。4)蒸发锋随时间从PML表面向下移动。5)蒸发锋面以上PML中的水汽以分子扩散和湍流扩散的方式输送。PML表面附近的运动主要是由后者引起的。玻璃微珠的混合长度是颗粒直径的一半数量级。

项目成果

Ishihara Yasuo etal.: Proc. of the APD of the International Association for Hydraulic Research,6th Congress, Kyoto, Japan. (1988)

石原康夫等人：Proc。

Ishihara, Yasuo et al: "Water Vapour Transfer in Evaporation from a Bare Land" Proc. of the APD of the International Association for Hydraulic Research, 6th Congress, Kyoto, Japan. (1988)

Ishihara、Yasuo 等人：“裸地蒸发中的水蒸气传输”Proc。