A Method to Measure the Permeability of Dry Fiber Mats

Close to the finalization of the medium density fiberboard process, a fairly thick bed of loosely entangled fibers is compressed in a belt-press to often less than a tenth of its original unstressed thickness. This single unit operation is very important to consider when the manufacturing process of the boards is to be optimized. Despite this, there is a lack of knowledge of the interaction between the fiber mat strength and how the fluid flows through it, i.e. de-aeration. Thus, it is of greatest importance to find reliable methods for studying this stage of the manufacturing process. Following this quest, a method is developed with which the gas permeability of fiber mats can be measured. The method offers the potential to measure the permeability at different flow rates and thus at arbitrary pressure gradients through the material. The method is successfully validated with a porous reference material consisting of polymer spheres, and it is shown that the flow follows Darcy's law at the flow rates of interest. Finally, the method is demonstrated by a presentation of permeability measurements on fiber mats consisting of spruce fibers

CFD-modellering av selektiv icke-katalytisk reduktion av NOX under tillverkning av järnmalmspellets

Syftet med projektet är att utreda om rökgasreningstekniken selektiv icke-katalytiskreduktion (SNCR) kan användas till NOX-reduktion under tillverkning av järnmalmspellets.Tekniken har till vår vetskap aldrig använts i detta sammanhang. SNCR-tekniken innebäratt man vid hög temperatur injicerar ett reduktionsmedel i rökgaserna vilket reagerar medkväveoxiderna och bildar kvävgas och vattenånga.En strömningsmekanisk beräkningsmodell av processen har tagits fram och numeriskasimuleringar har genomförts med en kommersiell kod för att lösa flödesfältet. Sedaninkluderades en modell för sprayinjektion i processen vilket möjliggjorde en undersökningav den övergripande mixningen mellan de injicerade dropparna och den NOX-förorenaderökgasen. Det övergripande resultatet är att SNCR-tekniken fungerar med urea somreduktionsmedel men inte med ammoniak.Godkänd; 2011; 20111010 (ysko

A Subgrid-Scale Model for Turbulent Flow in Porous Media

Given the analogy between the filtered equations of large eddy simulation and volume-averaged Navier–Stokes equations in porous media, a subgrid-scale model is presented to account for the residual stresses within the porous medium. The proposed model is based on the kinetic energy balance of the filtered velocity field within a pore; hence, when using the model, numerical simulations of the turbulent flow in the pores are not required. The accuracy of the model is validated with available data in the literature on turbulent flow through packed beds and staggered arrangement of square cylinders. The validation yields that the model successfully captures the effect of the pore-scale turbulent motion. The model is then used to study turbulent flow in a wall-bounded porous media to assess its accuracy.Validerad;2019;Nivå 2;2019-10-01 (johcin)</p

Turbulent sekundärflöde i semicirkulära kanaler

Godkänd; 2011; 20111010 (ysko

Investigation of Post-Darcy Flow in Thin Porous Media

We present numerical simulations of post-Darcy flow in thin porous medium: one consisting of staggered arrangements of circular cylinders and one random distribution of cylinders bounded between walls. The simulations span a range of Reynolds numbers, 40 to 4000, where the pressure drop varies nonlinearly with the average velocity, covering nonlinear laminar flow to the fully turbulent regime. The results are compared to those obtained by replacing the bounding walls with symmetric boundaries with the aim to reveal the effect of bounding walls on microscopic characteristics and macroscopic measures, i.e., pressure drop, hydrodynamic dispersion and Reynolds stresses. We use large eddy simulation to directly calculate the Reynolds stresses and turbulent intensity. The simulations show that vortical structures emerge at the boundary between the cylinders and the bounding walls causing a difference between the microscopic flow in the confined and non-confined porous media. This affects the averaged values of pressure drop, the hydrodynamic dispersion and the Reynolds stresses. Finally, the distance between the bounding walls is altered with the particle Reynolds number kept constant. It is observed that the difference between results calculated in confined and non-confined cases increases when the bounding walls are narrower

Interaction between the flow in two nearby pores within a porous material during transitional and turbulent flow

The transition from laminar to turbulent flow in porous media is studied with a pore doublet model consisting of pipes with different diameter. The pressure drop over all pipes is recorded by pressure transducers for different flow rates. Results show that the flow in the parallel pipes is redistributed when turbulent slugs pass through one of them and six different flow zones were identified by studying the difference between the Re in the parallel pipes. Each flow zone starts when the flow regime of one of the pipe changes. Transitional flow of each pipe increases the correlation between different pipes pressure drop fluctuations. Frequency analysis of the pressure drops show that the larger pipe makes the system to oscillate by the presence of turbulent patches in its flow. However, when the flow in the smaller pipe enters into the transitional zone the larger pipe starts to follow the fluctuations of the smaller pipe.Validerad; 2015; Nivå 2; 20140329 (stlu

Modelling particulate flow during impregnation of dual-scale fabrics

Filtration of particles during impregnation of dual-scale fabrics is studied numerically for a number of configurations with a previously derived model. The initial position and size of the particles are varied. The main result is that structural composites can be tailor-made as to additional properties by such an approach.Godkänd; 2011; 20130418 (ysko