Search

The issue of maintaining low-gradient combustion in the conditions of high heat extraction has been investigated numerically in this work. The analyses include the application of a convective boundary condition at the wall (with estimated boiling heat transfer coefficient); analysis of the Internal Recirculation Device's impact on combustion products and heat transfer under low-gradient conditions; and comparison of both traditional and low-gradient combustion modes. It was shown that the Internal Recirculation Device material and geometry has a significant impact on the nitrogen oxide (NO x ) formation mechanism, as NO 2 emission becomes predominant and can rise up to several hundreds ppm. What is more, along with decrease in thermal resistance of the IRD, CO emissions also increase rapidly, even achieving over 2000 ppm. Additionally, the convective heat transfer rate decreased by about 25% after switching from traditional to low-gradient combustion, whereas the radiative mechanism increased by ≈40% compared to traditional mode. It should also be mentioned that the low-gradient combustion applied in this work achieved approximately 10% higher efficiency than conventional combustion. [ABSTRACT FROM AUTHOR]

This paper deals with the numerical simulation of a pilot-scale axial cyclone separator. The main purpose of this paper is to develop a numerical model that is able to foresee the cyclone separator cut-off point. This is crucial in blast furnace gas installation to capture large particles containing carbon and iron, while allowing smaller particles such as zinc and lead to pass through. The cut-off point must be designed to give a sufficiently high zinc and lead content in the sludge created after the second cleaning stage. This allows the sludge to become a commercial product. To design this cut-off point, an investigation of the influence of inlet gas velocity, temperature, and the angle of guiding vanes at the inlet was done. The developed CFD model was validated against experimental data on the fractional efficiency of the cyclone separator. The results were in good agreement with the experimental data for all parameters tested. The behavior of the particles inside the cyclone was also physically correct. [ABSTRACT FROM AUTHOR]

Combi-steamer condensation hoods are widely used in modern gastronomy. They condense steam produced by the combi-steamer and also filter solid particles, moisture, grease and smells. All these factors negatively affect the staff and dishes, so efficient work of the condensation hoods becomes important. A mathematical and experimental analysis of such a device is described in this paper. First a measurement methodology was designed and measurements of air humidity, temperature and mass flow rates were performed. The measurement procedure concerned dedicated a steam generator and combi-steamer. Next a mathematical model was developed. It was based on mass and energy balances of the condensation hood. The condensate flow rate turned out to be insufficient to fulfill the energy balance while measured directly. Hence, it was calculated from heater's power of the steam generator and the balance model was validated. The combisteamer had an unknown output, so the condensate flow rate was provided by the balance model after its validation. A preliminary diagnosis of the device was carried out as well. [ABSTRACT FROM AUTHOR]

In this paper, the authors proposed an inverse analysis using an in–house three-dimensional finite element method for the extraction of thermal conductivity tensor components of carbon-fiber/epoxy composite, based on the recorded thermographic data in the form of laser-induced temperature field. The core of the computational algorithm used for determining the thermal conductivity values (tensor components) consists of finite element solver, which operates in a hybrid mode with an analytical model. The presented method evaluates the thermal conductivity values by matching the calculated spatial and temporal temperature fields to the experimental data. Due to the specific nature of the measurement process and computational algorithm, the proposed technique is very efficient and allows for relatively rapid obtainment of the thermal conductivity values. For considered in this work composite material with 34% fiber volume fraction the experimental thermal conductivity values in transverse and parallel to the fiber directions were equal to 0.32 W/mK and 6.80 W/mK, respectively. Additionally, in order to verify the reliability of the presented methodology, the selected isotropic reference material was investigated, using the same testing procedure. The results obtained by using this novel approach are in good agreement with data measured using the conventional testing techniques. [ABSTRACT FROM AUTHOR]

The development of a numerical model and design for the innovative construction of a heat exchanger (HE) used in a condensation hood (being a part of the combi-steamer) are described in this work. The model covers an air-steam flow, heat transfer, and a steam condensation process. The last two processes were implemented with the use of an in-house model introduced via User Defined Functions (UDF). As the condensate volume is negligible compared to the steam, the proposed model removes the condensate from the domain. This approach enabled the usage of a single-phase flow for both air and steam using a species transport model. As a consequence, a significant mesh and computation time reduction were achieved. The new heat exchanger is characterised by reorganised fluid flow and by externally finned pipes (contrary to the original construction, where internally finned pipes were used). This allowed a reduction in the number of the pipes from 48 to 5, which significantly simplifies construction and manufacturing process of the HE. The redesigned HE was tested in two cases: one simulating normal working conditions with a combi-steamer, the other with extremely high heat load. Measurement data showed that the numerical model predicted condensate mass flow rate (3.67 g/s computed and 3.56 g/s measured) and that the condensation capability increased at least by 15% when compared to the original HE design. [ABSTRACT FROM AUTHOR]

Low-gradient combustion (LGC) proved to be an effective alternative technology to reduce pollutant emissions and carbon footprint, specifically when combined with hydrogen as a fuel or blend component. This novel technology offers several advantages over conventional combustion regimes, including a more effective control of emissions and providing greater flexibility in fuel application. The impact of hydrogen on this regime is still not well-known, especially when it comes to the combustion of pure hydrogen and fuels with a high hydrogen content. In the last two decades, numerical simulations have become a powerful tool that facilitates the research and design of LGC, particularly in terms of stability of the process and the emission of pollutants. This article provides an up-to-date review of recent trends and theoretical knowledge in low-gradient combustion. This includes the guidelines and recommendations applied to LGC modelling. Comparisons have been made between the recently published modelling approaches presented by the authors, including a detailed assessment of the discrepancies in the temperature predictions. The challenges and limitations associated with the LGC combustion modelling of conventional fuels (i.e., natural gas, methane, syngas) blended with hydrogen are also discussed. The review demonstrated that the Eddy Dissipation Concept (EDC) is the most common turbulent-chemical interaction model employed in LGC combustion simulations. The performance of the EDC can be significantly improved by variable constants C γ and C τ based on local turbulent Reynolds and Damköhler numbers. However, the most recent publications indicate that the flamelet-based approach can be considered as a promising (and more cost-effective) alternative to the EDC. Furthermore, the chemical kinetic studies considered in this review confirm that there is no detailed reaction mechanism capable of accurately predicting the temperature profile along with the emissions of the main species of interest, i.e., NOx, CO, CO2, and OH. Although GRI-Mech 2.11 is the most widely used mechanism in LGC simulations, providing satisfactory overall accuracy. • The issues associated with chemical kinetics modelling have been discussed. • Spatial discretisation and turbulence modelling have been deeply analysed. • Eddy Dissipation Concept modifications are described. • Errors of temperature predictions are computed and compared. • The effects of pure hydrogen and hydrogen blends application have been assessed. [ABSTRACT FROM AUTHOR]