LABORATORY INVESTIGATION OF THE HEAT TRANSFER CHARACTERISTICS OF A TRAPEZOIDAL CRUSHED-ROCK LAYER UNDER IMPERMEABLE AND PERMEABLE BOUNDARIES

摘要

Crushed-rock layer can be taken as a highly porous medium, which is often used in highway/railway embankment of permafrost regions. In this study, in order to investigate the characteristics of heat transfer of a trapezoidal crushed-rock layer, laboratory tests were carried out on the porous material with impermeable and permeable boundaries under wind condition. Case 1 was closed crushed-rock layer and Case 2 was open crushed-rock layer. The results for the two cases were analyzed and compared with each other. It can be concluded that the heat transfer rate of Case 2 is higher than that of Case 1, but long-term cooling capability of Case 1 is larger than that of Case 2 under the same experimental conditions. Furthermore, we found that the heat transfer mechanisms of the two cases are quite different from each other, namely, the energy exchange of the Case 1 mainly relies on the internal natural convection which is caused by thermal variations, while in Case 2 it is from the heat transfer enhancement because of the internal forced convection induced by the external air flow. Therefore, the boundary conditions (impermeable and permeable) of crushed-rock layer can have a very large impact on the heat transfer pattern, especially under windy condition.