This paper is concerned with the simulation of multiphase flow hydrodynamics in an experimental oxyfuel fluidized bed combustor designed for biomass fuels. The aim is to perform cross-validation between several models and solvers that differ in the description of some phenomena in question. We focus on the influence of turbulence modeling, inter-phase drag force models, the presence of biomass in the mixture. Also the possibility to simplify the full 3D description to a quasi-1D model is tested. However, the results indicate that such simplification is not suitable for chaotic phenomena in considered scenarios. The models were developed using ANSYS Fluent and OpenFOAM CFD software packages as well as our in-house CFD code CFBSim. The quantities relevant for comparison (the densities of the dispersed solid phases and the phase velocities) are presented in the form of cross-section averaged vertical profiles.
<p>Freezing and thawing cycles in laboratory were studied. Freezing-thawing cycles were carried out in the laboratory on fully saturated packed sand sample (15 cm in diameter and 20 cm in height). Series of freezing-thawing cycles were conducted with newly designed experimental setup. The setup consisted of inner plastic tube covered on its sides and outer plastic tube. The column sample was placed into the precisely controlled freezer chamber. The top of the sample was covered by an aluminum lid. Initially the sample was equilibrated at +10 &#176;C then the temperature inside the chamber was changed to -10 &#176;C. The inner temperature of the sample was monitored in three depths by thin temperature sensors (109 SS, Campbell Scientific, USA) horizontally inserted into the sample. The experiment aims to provide information on freezing dynamics and thermo-mechanical changes during the freezing and thawing cycles. Horizontal gradient within freezing cycle was monitored. The data were compared with simulations obtained by a numerical model (&#381;&#225;k et al., 2013). The model is based on the heat balance within the sample assembly and a modified heat equation for the porous medium temperature allowing for the phase transition below the freezing point depression.&#160;</p>
This article analyses processes accompanying solidification of a liquid-saturated porous medium by means of thermomechanical balance and admitting difference in density of liquid and solid phases. Complexity of these processes is given by the inherent heterogeneity of the volume occupied both by grains and pores of the medium. To understand details, we consider elementary pore configuration at the micro-scale. We have developed a micro-scale model describing mechanical, thermal, and phase change processes within a porous medium. The model provides spatio-temporal dependences of key variables and allows to evaluate the stresses caused by the difference in the specific volumes of the present phases.
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