A thermo fluid dynamic model of wood particle gasification and combustion processes

In order to qualitatively understand and evaluate the thermo-fluid dynamic situation within a wood gasification reactor, a 1D particle model has been created. The presented tool accounts for the highly in-stationary, kinetic- and thermo-chemical effects, leading to partial gasification and combustion of a wood particle embedded within a packed bed collective. It considers the fluid- dynamic situation within the changing porous bulk structure of the packed bed, its impact on species – and heat transition mechanisms, the energy – and mass balances of wood, coal, pyrolysis-gas, wood- gas and off-gas phases, the thermodynamics of locally developing gasification – and combustion reaction equilibria, as well as the presence of the chemical species hydrogen, water, carbon (di-) oxide, methane, oxygen, solid carbon and gaseous, longer chain hydrocarbons from pyrolysis. Model results can be shown to yield very good, qualitative agreement with measurements, found in literature

System dynamic modeling approach for resolving the thermo- chemistry of wood gasification

For Multiphysics problems that require a thorough understanding of multiple, influential, highly transient process parameters, a System Dynamic model can constitute either an alternative option, or a compact prelude to a more expensive 3-D Finite Element or Finite Volume model. As a rather uncommon example for the application of such a modelling method, this work presents a System Dynamic modelling concept, devised for resolving the thermo-chemistry within a wood gasification reactor. It compares the modelling concept as well as its results to a classic, thermo-chemical solution algorithm based on the minimization of LaGrangian Multipliers for resolving the gasification equilibrium equations. In contrast to the latter, the System Dynamic solver can consider the impact of reaction kinetics as well as molecular mass transfer effects on the gasification equilibrium. Thus the transient production rates of methane, hydrogen, carbon (di-) oxide and water, as well as the residual amounts of pyrolysis gas and oxygen, which occur during the gasification of a wood particle, can be predicted.

Model based analysis of forced and natural convection effects in an electrochemical cell

High purity copper, suitable for electrical applications, can only be obtained by electro-winning. The hallmark of this process is its self-induced natural convection through density variations of the electrolyte at both anode and cathode. In order to accelerate the process, first its full dynamic complexity needs to be understood. Thus, an OpenFoam®-based 2D model has been created. This finite-volume multiphysics approach solves the laminar momentum and copper-ion species conservation equations, as well as local copper-ion conversion kinetics. It uses a Boussinesq approximation to simulate the species-momentum coupling, namely natural draft forces induced by variations of the spatial copper concentration within the fluid. The model shows good agreement with benchmark-cases of real-life electrochemical cells found in literature. An additional flow was imposed at the bottom of a small-scale electrochemical cell in order to increase the ionic transport and thereby increase the overall performance of the cell. In a small-scale electrochemical cell in strictly laminar flow, the overall performance could be increased and stratification decreased

CFD modelling of pressure and shear rate in torsionally vibrating structures using ANSYS CFX and COMSOL multiphysics

This paper discusses numerical methodologies to simulate micro vibrations on a nontrivial torsionally oscillating structure. The torsional structure is the tip of a viscosity-density sensor using micro vibrations to measure the fluid properties. A 2D transient simulation of the fluid domain surrounding the tip of the sensor has been conducted in ANSYS CFX and COMSOL Multiphysics software. ANSYS CFX uses a frame of reference to induce the micro vibration whereas a moving wall approach is used in COMSOL Multiphysics for the full Navier-Stokes equation as well as their linearized form. The shear rate and pressure amplitude have been compared between the different numerical approaches. The obtained results show good agreement for both pressure and shear rate amplitudes in all models

Response of armour steel plates to localised air blast load : a dimensional analysis

We report on the results of dimensional analyses on the dynamic plastic response of square armour steel plates due to detonation of proximal cylindrical charges and ensued air blast loading. By assuming a generic function for the blast load, which is multiplicative comprising its spatial and temporal parts, a set of 14 dimensionless parameters, representative of the load and plate deformation, were identified and recast in the form of dimensionless functions of stand-off to charge diameter ratio. Parametric studies were performed using commercial code ABAQUS’s module of Finite Element hydrocode using MMALE and MMAE techniques, and combined with regression analyses to quantify the dimensional parameters and the expressions for dimensionless functions. A few numerical studies with various FE mesh types were also performed to validate the transient deflections against the small-scale experiments. For pulse loading due to proximal charges of small orders of stand-off/charge diameter ratio, the magnitude of the transverse deflection increased abruptly with incremental decrease in stand-off, in contradistinction to the plate deformations at higher stand-offs where variations in displacement are smooth. This confirmed the existence of a stand-off at which a transition in behaviour takes place. For stand-off values less than charge diameter, a dimensionless energy absorbing effectiveness factor was considered to investigate the prediction of rupture in the plate corresponding to different charge masses. This factor is measured as a baseline parameter to predict, using solely numerical means, the blast loads which ensue rupture on full-scale prototypes

Procedure for experimental data assessment for numerical solver validation in the context of model based prediction of powder coating patterns

In the scope of this study an experimental powder coating setup is designed and the method to extract statistically significant trends from the data generated is developed. The ultimate goals are to i) validate a previously developed 3D Euler-LaGrangian numerical solver and to ii) characterize the essential parameters for industrial powder coating processes in subsequent phases. The experiments involved coating a flat plate substrate with a corona spraying pistol. The resulting coating thickness has been quantified through the state of the art Coatmaster technology. The raw data generated from the Coatmaster has been filtered and rigorously analyzed to identify statistically significant trends. Furthermore, characteristic variables have been constructed for subsequent comparison to the numerical solver. This study reveals the challenges involved in assessing experimental data to extract meaningful comparisons for numerical solver validation

A simple instrument to measure the thermal transport properties of the human skin

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The evaluation of the skin thermal properties is relevant for many applications ranging from clinical dermatology to cosmetology. We introduce a simple passive device, capable of rapidly measuring skin thermal parameters using transient surface temperature measurements. Thanks to the development of an analytic thermodynamic skin model, tissue thermal diffusivity can be extracted from experimental data. For validation purposes, the thermal response of the apparatus has been modelled using a layered finite-element 3D model of the skin in thermal contact with a metallic measuring tip. Simplified 1D analytical and semi-analytical models have also been developed with the intent of modelling the thermal properties of the skin surface. The simplified models can be used to fit the thermal response measured by the device and to extract the thermal diffusivity in real time

Faraday instability in small vessels under vertical vibration

The formation of Faraday waves in a liquid inside a cylindrical vessel under the influence of vertical vibration is studied. The stability thresholds and its mode decomposition are obtained using a linear stability analysis. The stability model is validated with a vibration experiment in a vertical vibration table. The Faraday instability threshold is found for accelerations ranging from 0.1 to 1.0 times the gravitational acceleration. The confinement effect by the vessel introduces cut-off the low frequency modes and the allowed frequencies are discretized. The resulting acceleration stability threshold is high at low frequencies and it is the lowest at medium frequencies, 10-70 Hz, where the discretization of the mode k-momenta introduces low stability regions delimited by more stable frequency ranges. The relevance of these characteristics for the agitation of liquids will be discussed

Dynamic analysis of cylindrical shells subject to multiple blasts using FSI

Localised pressure pulse loads can pose a significant threat to structural elements and critical equipment and may cause failure and damage in the target due to the concentrated energy delivered upon a localised area of the target. The impulse impinged upon the local area at the contact interface can exceed 80% of the total impulse that the charge can deliver upon the infinite target, leading to potential perforation of the structural element. When multiple charges are detonated, the advection of gaseous products depends, among other parameters such as fluid density, on the type of blast wave interference and superposition. This work examines the influence of multiple charge detonations blasted in the air on the external surface of cylindrical shells. Two types of detonations were considered, viz. simultaneous and sequential. In both cases the charges were positioned at 50mm and 75mm stand-off to the right and left of the shell. The Fluid-Structure Interaction (FSI) phenomenon was investigated in each scenario. The pressure registered with the gauge points of the rigid target was implemented in an uncoupled study on a flexible target which demonstrated different mode shapes occurring in the shell due to each blast scenario. A dimensionless impulse parameter was defined based on the Gaussian distribution function associated with the load shape, which renders the probability of the impulse as the total impulse that can potentially be imparted to the target

FSI of viscosity measuring mechanical resonators : theoretical and experimental analysis

Measuring viscosity online in processes is crucial to maintaining the quality of many chemical and biological processes. The damping induced by the liquid around the resonator is used to determine the viscosity of the liquids. Typical viscosity sensors are probe style and obstruct the piping system, disturbing the flow and creating a potential source of contamination in critical processes. The eventual goal is to design a non-intrusive sensor capable of accurately measuring the viscosity of the liquids without influencing the flow within the pipe. In order to get a deeper insight into the functionality of such a device, a mathematical model has been developed describing the mechanical vibration coupled with the fluid-structure interaction (FSI) models. The shear stresses at the wall have been analysed using the computational fluid dynamics tool OpenFOAM and have been integrated into the derived model. For validation, the model has been tested against the samples. The model is capable of accurately predicting the response of the sensor and can be used as an optimization and design tool