Experimental study on convection characteristics of crushed-rock layer

Abstract

Research on the measurement of micro wind-velocity and the airflow characteristics in the crushed-rock layer, which is caused by temperature difference, has long been problematic. For the first time, this study obtains the airflow characteristics in a crushed-rock layer by using high-precision micro wind-velocity detectors. Based on the experimental results, this study verifies the theory that the crushed-rock layer is available for convection heat exchange of porous media in a limited space. In boundary temperature fluctuations conditions, the cooling process is closely related to the natural convection process in the crushed-rock layer, and cooling occurs rapidly during the convection heat transfer process. The warming process, which occurs by heat conduction, happens gradually over a relatively long period of time, resulting in asymmetrical temperature change. The convection process exists only in the increasing and decreasing cooling stages of the entire cooling stage. The temperature difference between the top and the bottom in the crushed-rock layer is a key factor for the occurrence of convection and its intensity, although the air temperature changes also have an effect on the natural convection process in the increasing and decreasing cooling stages. Pore-air natural convection velocity increase is related to the increase in the temperature difference. Due to the different temperature and the penetration resistance of the crushed-rock layer, the velocity rapidly decreases in the depth direction, and there exits a delay phenomenon, so better cooling effect is in accordance with an optimal thickness of the crushed-rock layer.