scholarly journals Establishment of Intrinsic Permeability of Coarse Open-Graded Materials: Review and Analysis of Existing Data from Natural Air Convection Tests

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 767
Author(s):  
Karlis Rieksts ◽  
Inge Hoff ◽  
Elena Scibilia ◽  
Jean Côté
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Shape Effect ◽  
Intrinsic Permeability ◽  
Graded Materials ◽  
Square Enclosure ◽  
Air Convection ◽  
Degree Of Confidence ◽  
Physical Shape ◽  
Frost Penetration

This paper presents a review and analysis of large-scale air convection tests and the establishment of intrinsic permeability in coarse open-graded materials. Natural air convection can make a significant contribution to heat transfer during cooling periods. In seasonally freezing environments this can result in excessive frost penetration and subsequent frost-related problems. Intrinsic permeability largely defines the onset of convective heat transfer in granular materials. Conventional methods for measuring intrinsic permeability cannot be applied to very coarse materials. Large-scale laboratory experiments on natural air convection can serve as an alternative method for determining this crucial parameter. This paper gives an overview of four different experimental test setups for measuring natural air convection, all differing in physical shape, boundary conditions and heat flux/temperature measurement devices. Comparison between these is difficult because the air convection pattern can differ and in some cases the shape and number of convection cells cannot be validated. Most of the studies available in the literature use theoretical equations to approximate intrinsic permeability. A method based on the analytical Nu-Ra number relationship is employed to establish the values of intrinsic permeability. Tests that provide enough data to enable the use of the Nu-Ra relationship are very limited. The overall results show a reasonable correlation between experiment-based intrinsic permeability and theoretical approximation. However, several issues must be addressed: first, differences may exist between the intrinsic permeability of natural and of crushed materials due to the shape effect. Second, the method used is in theory valid only for two-dimensional air convection within a square enclosure heated from below. Yet the results show that this method could be extended to other conditions with a certain degree of confidence. Third, a good estimate of intrinsic permeability is possible only with accurate experimental measurement.

Laboratory investigations into convective heat transfer in road construction materials

2020 ◽  
Vol 57 (7) ◽  
pp. 959-973 ◽  
Author(s):  
Karlis Rieksts ◽  
Inge Hoff ◽  
Elena Scibilia ◽  
Jean Côté
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Foam Glass ◽  
Construction Materials ◽  
Crushed Rock ◽  
Intrinsic Permeability ◽  
Rock Materials ◽  
Air Convection ◽  
Laboratory Investigations

This paper presents a laboratory investigation into natural air convection and the establishment of intrinsic permeability of road and railway construction materials. The laboratory investigations were performed using a heat transfer cell with an inner volume of 1 m3. The study shows the importance of natural air convection and a practical method for establishing the intrinsic permeability of coarse granular materials. Three different open-graded crushed rock materials and two lightweight aggregates were tested. All materials were tested for downward (conduction only) and upward (convection and conduction) heat flow conditions. The experimental results revealed that all three crushed rock materials are prone to developing natural air convection in thermal gradients of 4.5 to 11 °C/m, depending on the particle size distribution. Foam glass aggregates showed a convective heat transfer flow at the fairly low temperature gradient of 6.5 °C/m. No natural air convection was achieved in expanded clay aggregates within the temperature gradients imposed. Intrinsic permeability values were established based on the experimental results. The intrinsic permeability of crushed rock materials ranged from 1.1 to 2.2 × 10−6 m2 while that of foam glass materials was 0.9 × 10−6 m2.

Intrinsic permeability of materials ranging from sand to rock-fill using natural air convection tests

2011 ◽  
Vol 48 (5) ◽  
pp. 679-690 ◽  
Author(s):  
Jean Côté ◽  
Marie-Hélène Fillion ◽  
Jean-Marie Konrad
Keyword(s):  
Natural Convection ◽  
Experimental Results ◽  
Heat Extraction ◽  
Test Results ◽  
Intrinsic Permeability ◽  
Square Enclosure ◽  
Rock Fill ◽  
Air Convection ◽  
Effective Particle ◽  
Winter Time

Air convection within coarse rock-fills enhances winter-time heat extraction from underlying soils. Modeling this phenomenon requires the knowledge of intrinsic permeability. This study focuses on the measurement of intrinsic permeability using natural air convection within a 1 m3 test cell. Upward heat flow conditions are applied to various specimens. Test results are analyzed using a theoretical solution of natural convection in a square enclosure. Four materials were studied, with effective particle sizes (d10) ranging from 90 to 150 mm and porosities ranging from 0.37 to 0.41. The results showed that intrinsic permeability increases with increasing d10. The experimental results were adequately predicted by the Kozeny–Carman and Chapuis equations. Only slight deviations were observed, which is considered acceptable given that these equations were developed for materials with much smaller values of d10. The experimental results of this study confirm the value of intrinsic permeability recently used in a study of natural convection within a rock-fill dam in northern Quebec, Canada.

scholarly journals Finite cell method for functionally graded materials based on V-models and homogenized microstructures

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Benjamin Wassermann ◽  
Nina Korshunova ◽  
Stefan Kollmannsberger ◽  
Ernst Rank ◽  
Gershon Elber
Keyword(s):  
Functionally Graded Materials ◽  
Large Scale ◽  
Functionally Graded ◽  
Material Behavior ◽  
Modeling Framework ◽  
Finite Cell Method ◽  
Geometric Framework ◽  
Graded Materials ◽  
Cell Method ◽  
Finite Cell

AbstractThis paper proposes an extension of the finite cell method (FCM) to V-rep models, a novel geometric framework for volumetric representations. This combination of an embedded domain approach (FCM) and a new modeling framework (V-rep) forms the basis for an efficient and accurate simulation of mechanical artifacts, which are not only characterized by complex shapes but also by their non-standard interior structure. These types of objects gain more and more interest in the context of the new design opportunities opened by additive manufacturing, in particular when graded or micro-structured material is applied. Two different types of functionally graded materials (FGM) are considered: The first one, multi-material FGM is described using the inherent property of V-rep models to assign different properties throughout the interior of a domain. The second, single-material FGM—which is heterogeneously micro-structured—characterizes the effective material behavior of representative volume elements by homogenization and performs large-scale simulations using the embedded domain approach.

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