Laboratory investigations on heat transfer of coarse crushed rock materials

K. Rieksts, I. Hoff, E. Kuznetsova, J. Côté

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Cold Regions II

ABSTRACT: Design requirements for roads and railways in Norway allow the use of coarse open graded materials. For such materials, apart from the thermal conduction, natural air convection can yield a significant contribution to the overall heat transfer. This paper presents a laboratory study dealing with air convection tests for coarse materials. In addition, the tests serve as a good basis for defining the intrinsic permeability of these materials within a heat transfer cell with an inner volume of 1m3. One sample was prepared of natural cobbles with particle size ranging from 0.09 to 0.21 m and the corresponding d10 value of 0.12 m. The sample was tested under three temperature gradients for upward and downward heat flow. As expected, the experimental results show that for a given thermal gradient, the heat flux is larger for upward heat flux compared to downward heat flow. The analysis results yielded an average value of intrinsic permeability of 3.5 x 10-6 m2. This value is within the limits of intrinsic permeability of similar study performed with materials with similar particle size distribution. In addition, the results have a reasonably good agreement with values calculated by Kozeny-Carman and Chapius equations. This study serves as a validation for the test setup and the project will continue with measurements of air convection for crushed rock materials. Les exigences grossiers à porométrie ouverte. Pour de tels matériaux, hormis la conduction thermique, la convection naturelle peut contribuer significativement aux échanges de chaleur. Cet article présente une étude en laboratoire de la convection matériaux mique de 1 m3. Un échantillon de cailloux naturels a été préparé avec des dimensions de particules variant de 0,09 m à 0,21 m et un diamètre effectif d10 selon trois gradients thermiques pour des écoulements de chaleur descendant et ascendant, respectivement. Tel t donné une perméabilité intrinsèque de 3,5 x 10-6 m2antérieures sur des matériaux similaires. De plus, les résultats sont raisonnablement en accord les valeurs calculées avec les modèles de Kozeny-Carman et de Chapuis. Cette étude sert de validation de la cellule expérimentale et le projet se continuera avec des essais sur des matériaux de roc concassé.

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