边界条件对碎石层降温效果及机理的影响

对平均粒径为22.1 cm, 厚度1.3 m, 边界为开放和封闭的碎石层进行了一系列的实验. 从环境温度为最高和最低时刻封闭碎石层内的温度和速度分布可知: 当碎石层上表面温度低于下表面时,碎石层自下向上的散热由空气对流和碎石间的热传导来完成; 当上表面温度高于下表面时, 自上向下传递的热量由碎石接触面间的热传导完成, 此时, 由于其内部的空气几乎静止, 能阻隔热量的传入, 因此封闭边界的碎石层具有热半导体特性. 而开放边界的碎石层, 当平均温度为 0.5℃的空气从上表面吹过时, 碎石体内的热量传递主要是靠强迫对流来完成, 热半导体效果不明显, 不利于使其下面的冻土降温.

The Influence of Boundary Conditions on the Cooling Effect and Mechanism of Ripped-rock Layers

A series of experiments were for the crushed rock layers, whose average particle diameter is 22.1 cm and thickness is 1.3 m, with open and closed boundaries, respectively. According to the temperature and velocity distributions in the crushed rock layer with the closed boundaries when the environmental temperatures are at the highest and the lowest, respectively, it is found that when the temperatures on the top of the crushed rock layer are lower than that on the bottom, the heat from lower part to upper part in the inner of the crushed rock layer is transferred by means of air convection and thermal conduction among the crushed rocks; while the heat transfer from upper part to lower part is mainly finished by the thermal conduction among the crushed rocks when the temperatures are higher on the top than on the bottom, and at that time the air in the crushed rock layer almost kept constant, which could be an obstacle to the enter of the heat. So the crushed rock layer with the closed boundaries would be considered to have the characteristics of thermal semiconductor. But when the air with an average temperature of 0.5℃ crossed through the crushed rock layer with the open boundaries from its top, the thermal transfer is mainly finished by the forced convection, and the effect of thermal semiconductor is not obvious, which is not benefit to the decreasing temperature of the frozen soil under the crushed rock layer.