1,720,979 research outputs found
Numerical Simulation of Regenerative Chambers for Glass Production Plants with a Non-Equilibrium Heat Transfer Model
No full text
Analysis of the stability of centrifugal compressors for turbocharging application. Identification of criteria for the prediction of the stable operating limit
No full textA centrifugal compressor for turbocharging application often has to work in conditions far from optimal conditions, due to the different operating conditions it is subjected in an automotive application. Therefore, the knowledge of the operating limits of a centrifugal compressor is fundamental in a first design phase. In particular, can predict the surge limit range, at a given speedline, is a serious challenge. In the literature there are extensive studies on the phenomena that lead the compressor to work in unstable operation, in particular the rotating stall. However, there is a lack of precise methods that can establish with certainty the correct surge massflow rate. Nowadays with the ever increasing computational resources a large contribution can be provided by the CFD techniques. In this regard, in this thesis the main goal is to able to identify some criteria to predict the surge line, through simplified models, which do not require excessive computational resources. For the compressors with a vaned diffuser, a stability parameter is developed, which shows excellent reliability in this type of turbomachinery. However, in the case of compressors with vaneless diffuser, has been necessary to develop further criteria due to the loss of effectiveness of the previous criterion. In more details for the centrifugal compressors with vaneless diffuser, through a deep fluid dynamic analysis, has been possible to identify two different fields of application to develop the appropriate criteria, based on the fluid-dynamic phenomena that lead the compressor to unstable operation. In particular in this work, for the case with vaneless diffuser, the following criteria have been developed at the low rotational speed: the critical angle (a modified version respect to the Senoo’s criterion) and the recirculation zone at the diffuser, while for the impeller the criterion of the diffusion ratio. Finally, it has been shown how, increasing the rotational speed, the volute acquires a key role in the inception of unstable machine phenomena; so a criterion based on this last component has been developed for high rotational speed
A comparison of strategies to extend the operating range of radial compressors for turbocharging
Get PDFThe operating range extension of radial compressors is a crucial aspect in turbocharging the internal combustion engines in order to extend the operating range of the system at high efficiency for fuel and environmental impact reduction. The future scenario of automotive propulsion will have the fuel cells at the top of the ranking of possible reference systems in substitution of thermal reciprocating engines. Proton exchange membrane fuel cells for automotive or aerospace vehicles are frequently turbocharged because compressed air for the fuel cell stack is required in the cathode system. Therefore, like in turbocharged internal combustion engines, a radial compressor is combined and connected with a radial turbine to exploit the thermal energy of the exhaust gas from the fuel cell. The study and the development of this sort of radial turbomachinery is still strategic to guarantee high performance of the overall propulsion system. The operating range is an important issue and current turbocharger design must be adapted to the new requirements of the fuel cells systems with a need for extending it. Various techniques to extend the operating range of the centrifugal compressor have been investigated and a summary is reported in this work, with a focus on the casing treatment. Through a CFD simulation campaign with appropriate simplified models, the effects of installing the ported shroud, the shutter or the axial groove have been calculated with respect to a baseline configuration. These simulations have supported the identification of the main limits and advantages for each of these solutions at different operating regimes. The performance maps and some physical parameters of interest have been compared
Simulation of flame development in a glass furnace with hydrogen enriched natural gas
No full textThe glass manufacturing industry is energy demanding and has significant environmental impacts due to the high temperatures required for melting raw materials, resulting in pollutant emissions. With the EU's goal of climate neutrality by 2050, reducing energy consumption and emissions in glass production is a key priority. Integrating some quantities of hydrogen in the fuel mixture can offer a promising solution for decarbonization. While hydrogen is being explored in industries like steel, its potential as a clean fuel for glass furnaces still requires further research. This study focuses on the impact of introducing hydrogen into the fuel mixture for glass furnace combustion. Using an innovative CFD framework that overcomes the limitations of existing models—where combustion is typically treated with oversimplified approaches and the glass tank is solved separately via iterative coupling between domains—this work introduces a fully coupled simulation of both the combustion space and the glass bath within a single computational environment. The reactive flow is resolved using a reduced chemical kinetic mechanism in combination with the EDC (eddy dissipation concept) turbulence–chemistry interaction model, enabling an accurate representation of combustion development. This advanced setup is employed to assess the effect of hydrogen enrichment while maintaining the same overall thermal input power as the natural-gas-only baseline case. The results demonstrate that a 30 % hydrogen addition (by energy) can achieve a substantial reduction in CO2 emissions of nearly 30 % and a decrease in NO emissions of approximately 40 %, highlighting the significant environmental benefits of hydrogen enrichment, while simultaneously introducing serious flame stability challenges that must be carefully managed. This behaviour has been thoroughly analyzed, with particular focus on flame patterns, heat flow distribution and glass surface temperature. To address this challenge, some strategies are proposed to stabilize combustion, restoring stable flame conditions akin to those observed with natural gas. The study aims to explore hydrogen's potential in decarbonizing the glass industry, offering practical solutions for integrating hydrogen into production processes with promising results. This contributes to reducing industrial carbon emissions and supports the transition to a more sustainable energy system
Development of an analytical model to evaluate the effect of the ported shroud on centrifugal compressors
No full textExtending the operational range of centrifugal compressors is strategically vital for turbocharging internal combustion engines, particularly in enhancing efficiency and expanding operational capabilities. This extension is crucial for reducing environmental impact by enabling engines to perform more efficiently under a wider range of conditions. In the transition from conventional thermal reciprocating engines, fuel cells, especially proton exchange membrane fuel cells (PEMFCs), are emerging as strong alternatives. In automotive applications, PEMFCs often require turbocharging to supply compressed air to the cathode system of the fuel cell stack. This integration is essential for utilizing the heat from the fuel cell's waste products, thereby improving overall system efficiency. Ongoing research and development in radial turbomachinery are critical for optimizing the performance of these propulsion systems. Specifically, adapting turbocharger designs to meet the unique requirements of fuel cell systems and extending their operational range are essential tasks. Using a simplified CFD model, the impact of a ported shroud on compressor performance and range extension has been investigated. Flow structure analysis identified that the primary role of the ported shroud is to modify the relative flow angle on the rotor at the highest span channel. Additionally, a simplified analytical model was developed to quantify the effectiveness of different ported shroud geometries on the compressor by examining changes in tangential velocity after mixing with the flow from the cavity
The Use of Artificial Intelligence for Cooling Failure Detection in High-Pressure Turbine Blades
No full textModern High-Pressure Turbine (HPT) stages in aircraft engines are designed to operate at very high temperatures to maximize the engine performance and efficiency. Blade coatings and sophisticated cooling systems are the main strategies to safeguard the integrity of HPT blades from the hot combustion gases at temperatures even over 2000 K. The cooling flows, extracted from the compressor flow path, are channeled in a complex layout of pipes within the engine casing and the HPT blades. The engine control system must ensure continuous delivery of cooling gas because any interruptions could seriously compromise the blade integrity. Innovative techniques using Machine Learning combined with the Computational Fluid Dynamics (CFD) simulations can support the development of extended monitoring systems or control systems. With the HPT of the Energy Efficient Engine (E3) as reference case of a 3D cooled gas turbine blade, a database of CFD simulations (using the open-source turbomachinery software MULTALL) is performed by varying the cooling mass flow across different ejection zones in a single blade row, simulating real-world scenarios such as partial or full clogging. The use of the open-source platform allows the simulation of a large number of cases in parallel that would be prohibitively expensive for an academic research activity if based on commercial licenses. From the resulting CFD dataset, a large number of global parameters, that can be measured during engine operation, are extracted, together with the local spanwise temperature distributions near the leading and the trailing edge of the inspected row. The resulting database is used to train two Neural Networks models: the first one can reconstruct the temperature distributions from the few measurable parameters, the second one uses the reconstructed temperature profiles to understand if the cooling system has some malfunctioning and where this occurs (Leading Edge, Suction Side and Trailing Edge or Endwalls). In the paper the potential of the proposed approach for the setup of extended engine monitoring tools is demonstrated
CFD Modelling of Regenerative Pre-heating Systems for Recycled Glass Raw Material
No full textThe glass production industry has one of the highest energy consumption rates and environmental emission impact with respect to the existing industrial sectors. Moreover, the glass production sector is important in Italy (with production plants spread all over the country from North to South) from both production rates and engineering design and development competencies point of view. The glass furnaces are nowadays conceived with regenerative or recuperative systems to take advantage of the residual heat from the combustion exhausts in order to increase the thermal efficiency of the system. The exhaust gases are also used in innovative systems to reduce the NOx emissions in specifically designed gas recirculation systems tailored to the glass furnace. A remaining portion of the heat content in the exhaust gases could be used to pre-heat the raw material from recycled glass that, in some applications, forms a significant percentage of the glass recipe. In order to develop pre-heating systems for recycled glass as compact as possible, a detailed analysis of the heat transfer from the gases to the glass need to be developed. In the paper different CFD models for the heating process of recycled glass are presented. A numerical model for the recycled glass loose particles has been developed and used in the CFD models for both direct (the exhaust gases flow through the recycled glass matrix) and indirect (the recycled glass is heated through heat diffusion from the hot gases that flow into pipes) systems
Numerical strategies for fluid-dynamic and heat transfer simulation for regenerative chambers in glass production plants
No full textNumerical Simulation of Melted Glass Flow Structures inside a Glass Furnace with Different Heat Release Profiles from Combustion
No full textA glass production furnace requires a considerable amount of energy to allow the correct glass melting process. In this work, a CFD model has been developed in order to simulate the convective flow movements within the molten glass bath of the glass furnace. A heat flux profile has been assigned to the glass free surface to model the combustion process, and the glass has been modelled with thermophysical properties variable with temperature based on its chemical composition. The model has been validated by comparing the flow structure and temperature with a reference work. Subsequently, a flow analysis has been carried out by using different shapes for the heat flux profile and by varying its main parameters. The above heat release profiles are representative of different settings of the combustion operating points and can be useful to understand the effects of different flames (i.e., from different fuels also) on the glass flow structure. It has been demonstrated that only the thermal distribution with a maximum generates two convective macro-cells: the first is necessary for the glass melting, the second for its homogenization. It has also been observed that the length of these vortices is related to the flame length. However, a portion of the flow exits directly from the throat (furnace exit port) without entering into the second cell; a low-quality product will be generated in this case
- …
