The paper reports on the multi stage spray drying model of zeolite 4A suspension. The model builds on upgrading the single stage spray drying model, as used in majority of CFD codes, to a multistage drying model, suitable for the implementation in a multiphase Lagrange-Euler CFD code. In the model, the first stage describes drying of surface moisture, followed by the second stage, in which the moisture in the porous interior of the drying particle is removed. The second stage is governed by the semi open Stefan diffusion model. The removal of the remaining adsorbed moisture in the zeolite crystals is modeled in the third stage by a kinetic model, implementing the temperature vs. moisture gradient data, obtained from the thermogravimetry data for zeolite 4A-water system. The multistage drying model is validated by comparing computational results for the particle, immersed in the drying air under varying process conditions alongside typical particle trajectories, obtained from the CFD analysis of a pilot scale dryer. The results obtained from the numerical model are compared with experimental results, obtained from performing several tests on the pilot scale spray dryer, and confirm the applicability and physical correctness of the proposed model.
COBISS.SI-ID: 20122390
The aim of the study was to test the possibility of replacing mineral diesel fuel with biodiesel fuel made from rapeseed oil. The engine’s performance, in-cylinder pressure, fuel consumption, and the amount of produced NOx and CO emissions were monitored during experimental measurements, which were repeated numerically using the AVL BOOST simulation program. New empirical sub-models are proposed for determining a combustion model and emission models parameters. The proposed sub-models allow the determination of necessary combustion and emission model parameters regarding the properties of the tested fuel and the engine speed. When increasing the percentage of biodiesel fuel within the fuel blends, the reduction in engine torque and brake mean effective pressures are obtained for most of the test regimes. The reduction is caused due to the lower calorific value of the biodiesel fuel. Higher oxygen content in biodiesel fuel contributes to a better oxidation process within the combustion chamber when running on pure biodiesel or its blends. Better oxidation further results in a reduction of the formatted carbon and nitrogen oxides. The reduction of carbon emission is also attributed to the biodiesel fuel’s lower carbon content. It can be concluded from the obtained results that neat biodiesel fuel and its blends with mineral diesel fuel can be used in heavy-duty diesel engines with mechanically controlled injection systems as replacements for mineral diesel fuel.
COBISS.SI-ID: 19267350
Numerical modelling is widely used in industry for detailed understanding of the combustion process and for appropriate design and optimization of biomass/waste-fired boilers. This paper presents a numerical study of a 13 MWth waste wood-fired grate boiler, based on the coupled in-bed fuel conversion modelling and freeboard combustion modelling methodology. A 1D model is developed for the conversion of the waste wood in the fuel bed on the grate, providing the appropriate grate inlet condition for the 3D simulation of the freeboard region. Since part of the flue gas is recycled into the boiler as an innovative attempt to improve the boiler performance, a refined weighted-sum-of-grey-gases-model of greater accuracy is developed to better address the impacts of the elevated CO2 and H2O vapour concentrations on radiative heat transfer in the boiler. The impacts of full buoyancy on the turbulent flow are also investigated. The temperature profiles at different ports in the furnace are measured to shed some light on the flow and combustion characteristics in the boiler and also to collect some in-flame data for modelling validation. The overall modelling strategy, the new sub-models and the use of recycled flue gas are all of great benefit or reference for modelling and design of grate-fired boilers.
COBISS.SI-ID: 19360022
The study focuses on a numerical investigation of biofuels' influence on an injected fuel-spray cone's angle and length, which have further influence on the combustion process and the formation of pollutants in internal combustion engines. The influence of different physical and chemical properties of pure mineral diesel fuel, biodiesel fuel and their blends on spray characteristics was investigated with the AVL FIRE simulation program. Several different empirical model parameters, usually the engine-operating regime and biofuel used, must be defined when using numerical models. In this study, the numerical model implemented in AVL FIRE was modified so that all model parameters were determined regarding biofuel properties and engine-operating conditions. Experimental measurements of spray development in a cylindrical chamber pressurized with nitrogen at 40-60 bar were performed for validation of the modified numerical model. Photos of spray development were taken with a high speed camera simultaneously with pressure and needle-lift signals. The comparison of experimental and numerical results confirmed the usability of the numerical model. Numerical results of spray development for different biofuels under different operating regimes and ambient pressure confirm the possible usage of biofuels as a replacement for mineral diesel fuel in diesel engines with the early generation of fuel injection systems.
COBISS.SI-ID: 18359830
A hybrid LES/URANS turbulent model for a BEM based turbulent fluid flow solver was developed. We employed the unified LES/URANS approach, where the interface between the LES and URANS regions is defined using a physical quantity, which dynamically changes during numerical simulation. The main characteristic of the unified hybrid model is that only one set of governing equations is used for fluid flow simulation in both the LES and URANS regions. Regions where turbulent kinetic energy is calculated by LES and URANS models are determined using a switching criterion. We used the Reynolds number based on turbulent kinetic energy and the Reynolds number based on total turbulent kinetic energy to establish the LES/URANS interface switching criterion. Depending on flow characteristics and with the use of switching criterion, we chose between sub-grid scale viscosity (SGS) and URANS effective viscosity. The SGS or URANS effective viscosity is used in the transport equation for turbulent kinetic energy and in governing equations for fluid flow. The developed numerical algorithm was tested by simulating turbulent natural convection within a square cavity. The hybrid turbulent model was implemented within a numerical algorithm based on the boundary element method, where single domain and sub-domain approaches are used.
COBISS.SI-ID: 18814742