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Numerical modeling of two-phase flow inside a wet flue gas absorber sump
Nejc Vovk, Jure Ravnik, 2023, original scientific article

Abstract: A numerical model of a flue gas scrubber sump is developed with the aim of enabling optimization of the design of the sump in order to reduce energy consumption. In this model, the multiphase flow of the continuous phase, i.e., water, and the dispersed phase, i.e., air bubbles, is considered. The air that is blown in front of the agitators, as well as the influence of the flow field of the agitators on the distribution of the dispersed phase and the recirculation pumps as outlet, is modeled. The bubble Sauter mean diameter is modeled using the population balance model. The model is used to analyze operating parameters such as the bubble retention time, the average air volume fraction, bubble Sauter mean diameter, the local distribution of the bubble size and the amount of air escaping from the pump outlets at two operating points. The purpose of the model is to simulate the two-phase flow in the sump of the flue gas scrubber using air dispersion technology with a combination of spargers and agitators, which, when optimized, reduces energy consumption by 33%. The results show that the homogeneity of air is lower in the bottom part of the absorber sump and that the amount of air escaping through recirculation pipes equals 1.2% of the total air blown into the absorber sump. The escaping air consists mainly of bubbles smaller than 6 mm. Additional operating point results show that halving the magnitude of the linear momentum source lowers the air retention, as well as the average homogeneity of the dispersed air
Keywords: flue gas scrubbing, air dispersion, numerical model, OpenFoam
Published in DKUM: 19.12.2023; Views: 223; Downloads: 14
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Analysis of the effect of the swirl flow intensity on combustion characteristics in liquid fuel powered confined swirling flames
Marko Klančišar, Tim Schloen, Matjaž Hriberšek, Niko Samec, 2016, original scientific article

Abstract: This article examines the implementation of CFD technology in the design of the industrial liquid fuel powered swirl flame burner. The coupling between the flow field and the combustion model is based on the eddy dissipation model. The choice of the LES (Large Eddy Simulation) turbulence model over standard RANS (Reynolds Averaged Navier-Stokes) offers a possibility to improve the quality of the combustion-flow field interaction. The Wall Adapting Local Eddy-Viscosity (WALE) sub-grid model was used. The reaction chemistry is a simple infinitely fast one step global irreversible reaction. The computational model was setup with the Ansys-CFX software. Through the detailed measurements of industrial size burner, it was possible to determine the natural operational state of the burner according to the type of fuel used. For the inlet conditions, axial and radial velocity components were calculated from known physical characteristics of both the fuel and air input, with the initial tangential velocity of the fuel assumed as 18% of the initial axial fuel velocity. Different swirl number (S) values were studied. Addition of a surplus (in comparison to conventional flame stabilization) of tangential air velocity component (W), the rotational component increases itself with a considerably high magnitude, contributing to the overall flame stabilization. The level of S especially influences the turbulent energy, its dissipation rate and turbulent (Reynolds) stresses. In the case of high swirl number values (S > 0,65) it is possible to divide the flow field in three principle areas: mixing area (fuel-air), where exothermal reactions are taking place, central recirculation area and outer recirculation area, which primarily contains the flow of burnt flue gases. The described model was used to determine the flow and chemical behavior, whereas the liquid atomization was accounted for by LISA (Linear Instability Sheet Atomization) model incorporating also the cavitation within injection boundary condition. The boundary conditions were determined based on the data from the experimental hot water system. Depending on system requirements, especially with continuous physical processes as well as the results of experimental measurements, the paper reports on determination of the mixing field and its intensity in the turbulent flow, the description of heat release and interaction of turbulent flow field and chemical kinetics in the case of confined swirling flames.
Keywords: CFD, fluid dispersion, combustion, industrial burner, confined swirling flame, two-phase flow
Published in DKUM: 04.08.2017; Views: 1331; Downloads: 382
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In-line higher order mode filters based on long highly uniform fiber tapers
Denis Đonlagić, 2006, original scientific article

Abstract: This paper presents a simple and effective design of taper-based higher order mode (HOM) filters that can effectively remove HOMs from the few-mode fibers. For this purpose, a taper manufacturing technique that allows the production of long and highly uniform tapers was developed. A filter performance was demonstrated on a standard single-mode telecommunication fiber operating at 850 nm. The HOM suppression was better than$-$39 dB, and the insertion loss ofthe fundamental mode was less than 0.15 dB.
Keywords: optical fibres, few moded fiber, fiber design, mode conversion, mode filter, noise figure, optical fiber dispersion, optical signal to noise, optical transmission systems, taper
Published in DKUM: 31.05.2012; Views: 2262; Downloads: 110
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Properties of UV-cured pigment prints on textile fabric
Branko Neral, Sonja Šostar-Turk, Bojana Vončina, 2006, original scientific article

Abstract: This paper studies and evaluates the UV-curing of pigment prints on textile fabric using a prototype UV scanner. A printing paste comprising synthetic thickener, emulgator, binder, pigment dispersion and photoinitiator was applied using a flat screen printing technique onto the cotton fabric, then dried and exposed to heat or UV-radiation under a mercury vapour lamp (200 W cm-2). The characteristics of cured prints such as paste add-on, colour properties, colour fastness to washing and dryžwet rubbing were evaluated, together with fabric stiffness. The effects of UV-curing were evaluated by Attenuated Total Reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The properties of the UV-cured pigment prints were compared with those of the thermal cured prints. Analyses of the obtained results helped to define the optimum composition of the photo reactive pigment paste, and the UV-curing conditions under which satisfactory results were obtained, comparable with those from the thermal curing method.
Keywords: textiles, textile printing, printing quality, pigment dispersion, UV-curing, binder, photoinitiator
Published in DKUM: 30.05.2012; Views: 2359; Downloads: 110
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