粒径对块石层自然对流特性影响的试验研究  

Experimental Study on the Influence of the Particle Diameter on the Natural Convection Characteristics of the Block Stone Layer

作　　者：卞晓琳[1] 何平[1] 吴青柏[2] 施烨辉[1] 

机构地区：[1]北京交通大学隧道及地下工程教育部工程研究中心,北京100044 [2]中国科学院冻土工程国家重点实验室,甘肃兰州730000

出　　处：《中国铁道科学》2011年第1期1-6,共6页China Railway Science

基　　金：国家自然科学基金资助项目(50778012);北京交通大学科技基金资助项目(2007RC001)

摘　　要：用粒径为5～8,8～15和15～20 cm的3种块石分别填筑成块石层模型,在实验室内研究它们的空气自然对流特性。结果表明,在块石层模型下表面保持20℃而上表面从20℃降至-20℃的过程中,模型内均产生了Benard流,而且模型内空气自然对流的强弱与块石的粒径有关,粒径为15～20 cm的块石层模型内气流速度最大,约为2.2 m.s-1;粒径为8～15 cm的最小,约为1.5 m.s-1,这种变化主要是由块石层内热弥散效应以及块石与空气间接触面积的改变而引起的。控温方式对空气自然对流影响的研究表明,由模型上表面降温所产生的空气自然对流效应强于在块石层模型下表面升温,故在实际工程中,冬季块石层内的空气自然对流更易于发生。针对模型内空气流速计算值均比实测值小的问题,建议在进行多孔块石结构对流换热理论计算时,应考虑块石层模型的假设条件、热弥散作用、流动惯性以及空气热物性随压力的变化等的影响。The block stone layer models were completed by filling three kinds of block stones with the particle diameters of 5-8, 8-15 and 15-20 cm respectively, and the natural convection characteristics were researched by laboratory experiments. The results show that, in the process of keeping the constant temperature 20 ℃ at the bottom surface and cooling the top surface from 20 to --20 ℃ the Benard convection has appeared in each model. The strength of the natural convection in the model has something to do with the particle diameter of the block stone. In the block stone layer model with the particle diameter of 15-20 cm, the flow velocity is the biggest, which is about 2.2 m · s^-1. While in the block stone layer model with the particle diameter of 8-15 cm, the flow velocity is the smallest, which is about 1.5 m · s^-1. These variations are mainly resulted from the effect of heat diffusion in the block stone layer as well as the change of the contact area between the block stone and the air. The influence of temperature control mode on natural convection was studied. The results indicate that the natural convection effect caused by cooling the top surface of the model is more intensive than that caused by heating the bottom surface of the model. Therefore, in practical engineering, the natural convection is more liable to occur in the block stone layer in winter. Besides, it indicates that the calculated values of the flow velocity in the model are smaller than the measured ones. It is suggested that the assumptions of the block stone layer model, the effect of heat diffusion, the flowing inertia and the change of thermophysical properties with the pressure, etc. should be taken into account in theoretically calculating the convective heat transfer of the porous block stone structure.

关 键 词：冻土 块石粒径 自然对流效应 流速场 

分 类 号：P642.14[天文地球—工程地质学] U213.14[天文地球—地质矿产勘探]