Experimental study on ventilation characteristics of a concrete-sphere layer and a crushed-rock layer

Abstract

A crushed-rock layer has been utilized to thermally stabilize the railway/highway embankments in permafrost regions as this porous layer performs an air convective cooling effect, which is primarily determined by the internal ventilation drag. To maximize the cooling effect, this study used wind tunnel experiments to test the ventilation characteristics and ventilation-drag parameters of the two porous media, i.e. a concrete-sphere layer and a crushed-rock layer, with different particle sizes. The experimental results indicate that significantly quadric relationships exist between the pressure gradient and the superficial velocity in both the concrete-sphere layer and crushed-rock layer with large particle sizes. The nonlinearity can be divided into a viscous loss term and an inertial loss term. It is also found that for the two media, their permeabilities and inertial resistance factors are significantly related to the mean particle sizes of the media. The crushed-rock layer is found to have a larger ventilation drag than the concrete-sphere layer under the same mean particle size because the crushed rocks have irregular shapes and coarse surfaces. These findings are helpful to numerically apply the heat and mass transfer theories in porous media to model the cooling effect of the crushed-rock embankments in permafrost regions.