Using the Reference Shrinkage Curve to Estimate the Corrected Crack Volume of a Soil Layer
To estimate the correct soil crack volume based on the shrinkage geometry factor, in addition to measurements with core samples, one also needs to know the shrinkage curve of the soil matrix without cracks. For such a curve one can use the soil reference shrinkage curve that is only stipulated by intraaggregate clay shrinkage without interaggregate cracking. The objective of this work is to illustrate such use of the reference shrinkage curve and, in addition, to argue the necessity to correct the usual estimates of the shrinkage geometry factor in order to correctly estimate the soil crack vol- ume. The illustration is based on available data and reference shrinkage curves for eight soils.
Assessing the role of the pore solution concentration on horizontal deformations in an unsaturated soil specimen during drying
Abstract Volume changes occurring in soil–water systems are the result of multi-scale interactions that affect several processes in the soil–water continuum. For example, the soil's shrinkage/swelling properties result in horizontal and vertical deformations at the soil specimen scale, and lead to cracking which is often responsible for producing preferential flow paths that impact the hydrologic response at the plot and field scales. In spite of their significance, a complete understanding of soils' deformations and their corresponding impact on volume change behavior continues to be a major challenge. This paper presents an approach to quantify and interpret the role of the pore solution concentration on horizontal deformations of unsaturated soils. Specifically, a restrained ring method (RRM) is integrated with digital image correlation (DIC) techniques to relate the internal soil stress (caused due to drying) to the shrinkage strain (deformation) that develops in the soil specimen. The experimental results are described in the context of the theory of drying while explicitly considering the effect of changes in the properties of the pore solution (i.e., surface tension, viscosity and density) induced by the addition of a binary salt (NaCl). The experimental results conform to fundamental expectations and thereby this approach facilitates a better understanding of volume changes in unsaturated soils exposed to saline environments.
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.