1,720,985 research outputs found
Microtomography of Soil and Soot Deposits: Analysis of Three-Dimensional Structures and Surface Morphology
No full textThe detrimental effects generated by the gas turbine fouling phenomenon are well known. Due to soil and soot particles ingestion, gas turbines experience performance drops related to greater fuel consumption and even lower efficiency. These effects are related to the modification of the shape and surface roughness of relevant surfaces (compressor and turbine blades and vanes, especially) due to the presence of a thin layer generated by micro/nano-sized particle adhesion. Such contaminants are swallowed by the unit and, as a function of the operating conditions, adhere to the surface, causing a sort of dangerous coating to the surface. In this work, a microtomography analysis of the deposited layer is reported. The deposited layer has been generated using micro-sized soil and soot powders under specific impact conditions and substrate surface roughness similar to those in the cold section of a gas turbine compressor. The microtomography analysis has been carried out using the beamline at the ELETTRA Sincrotrone research center. Thanks to the resolution of the beamline, the detection of the threedimensional internal structure of the soil and soot layers has revealed that within the layer, the structure is characterized by discontinuities. Soot and soil particles, even characterized by similar diameter distributions and test conditions, generate layer structures that differ by the magnitude, orientation, location of the internal discontinuities, and surface morphology (i.e., roughness). The comprehension of the packing process allows to understand the adhesion process and define general guidelines to predict the fouling phenomenon
Apparatus and methods for the calibration and correction of a polydispersed dust feeding system applied in multiphase flow experiments
No full textMultiphase flow experiments allow the understanding of complex interaction mechanisms between particles and fluid structures under controlled conditions. In standard test rigs, the airflow is mixed with precise dust amount continuously, and accurate knowledge of the aerosol amount injected is mandatory to achieve reliable measurements and results. This work proposes the experimental procedure for calibrating an aerosol dosing and injection system. The purpose-built calibration system layout is explained in detail. To give a general perspective of the procedure, four test powders commonly used in multiphase flow tests have been used: Alumina, Silicon Carbide, and two grades of standard soil named Arizona Road Dust. Methodologies and criticisms are reviewed and assessed, and the final results are given in the form of calibration curves of the feeding system. Since the proposed correction is based on powder and flow characteristics, the proposed methodology can be applied to several cases and conditions
A Simplified Method for the Deposition Rate Assessment on the Vanes of a Multistage Axial-Flow Compressor
No full textGas turbine particle ingestion may lead to the deposition of contaminants in the compressor section, inducing the performance losses of the whole engine. The economic losses derived from this issue push great interest in the investigation of such a phenomenon from a numerical and experimental standpoint. This article describes a quantitative approach to predict particle deposition on the vanes of an axial compressor starting from the flow field obtained employing computational fluid dynamic (CFD) simulations. The results are then compared to the experiments performed on the Allison 250 C18 compressor unit subject to particle ingestion under controlled conditions. The results derived from the experimental and numerical investigations are presented, providing insight into the mass deposited on the vanes and the corresponding zones most affected by the particle deposition issue. The methodology showed good agreement in the estimation of the predicted values of the deposited mass and the corresponding patterns through the compressor stages. The low-complexity approach proposed here could help the designer to predict the contamination of the stationary rows starting from a simple set of single-phase numerical results. Furthermore, with the implementation of this approach into the design path, the designer could reduce the impact of fouling, looking at the effects of their solutions under the fouling-reduction light
Microstructural and erosive wear characteristics of a high chromium cast iron
No full textSurface material loss due to erosive wear is responsible for the increased cost of main-tenance and downtime in industries. Hence, hardfacing is one of the most valuable and effective techniques employed to improve the wear resistance of heavy-duty components. The present paper investigates the microstructural and erosive wear characteristics of a hypereutectic high-chromium cast iron, considering the erosion resistance, resulting from the impact of micro-sized particles, of both as-received and heat-treated conditions. Micro-sized particles involve the erosion-resistant characteristics of carbide and matrix, contemporary. Due to this, the enhancement of the matrix strength could improve the mechanical support to withstand cracking deformation and spalling. Ac-cordingly, the effect of a destabilization heat treatment on the microstructure was firstly investigated by hardness tests, X-ray diffraction analyses, optical and scanning electron microscopy. Specifically designed erosive tests were carried out using a raw meal powder at an impingement angle of 90◦ . The resulting superior wear resistance of the heat-treated samples was relayed on the improved matrix microstructure: consistent with the observed eroded surfaces, the reduced matrix/carbides hardness difference of the heat-treated material is pivotal in enhancing the erosion resistance of the hardfacing. The present results contribute to a better understanding of the microstructure–property relationships concerning the erosive wear resistance
A Stochastic Model for Nanoparticle Deposits Growth
No full textNatural events and human activities are responsible for the generation and transport of large amounts of microsized particles, which could contaminate several engineering devices like solar panels, wind turbines, and aero-engines. In industrial processes, systems as heat exchangers, fans, and dust collectors are continuously affected by nanoparticles’ interaction. For several applications, the adhesion of such nanoparticles is detrimental, generating safety and performance issues. Particle-to-particle and particle-to-surface interactions are well known, even if a general explanation of nanoparticle deposit growth is still unknown. In this paper, an interpretation of deposit growth due to nanoparticle deposition can predict particle adhesion, and layer accretion is proposed. A statistical model and a set of coefficients are used to generalize nanoparticle deposits’ growth by an S-shaped function. In particular, the nanoparticle deposits grow analogously to a typical autonomous population settlement in a virgin area following statistical rule, which includes the initial growth, the successive stable condition (development), and catastrophic events able to destroy the layer. This approach generalizes nanoparticle adhesion/deposition behavior, overpassing the constraints reported in common deposition models, mainly focused on the mechanical aspect of the nanoparticle impact event. The catastrophic events, such as layer detachment, are modeled with a Poisson’s distribution, related to material characteristics and impact conditions. This innovative approach, analogies, and coefficients applied to common engineering applications may be the starting point for improving the prediction capability of nanoparticle deposition
A quantitative approach for the estimation of the fouling rate on the stationary parts of a multistage test compressor
No full textGas turbine particle ingestion may lead to the deposition of contaminants in the compressor section, inducing the performance losses of the whole engine. The economic losses derived from this issue push great interest in the investigation of such a phenomenon from a numerical and experimental standpoint. This paper describes a quantitative approach to predict particle deposition on the vanes of an axial compressor starting from the flow field obtained employing CFD simulations. The results are then compared to the experiments performed on the Allison 250 C18 compressor unit subject to particle ingestion under controlled conditions. The results derived from the experimental and numerical investigations are presented, providing insight into the mass deposited on the vanes and the corresponding zones most affected by the particle deposition issue. The numerical model showed good agreement in the estimation of the predicted values of the deposited mass and the corresponding patterns through the compressor stages. The low-complexity approach proposed here, helps the designer to predict the contamination of the stationary rows starting from a simple set of single-phase numerical results. Furthermore, with the implementation of this approach into the design path, the designer could reduce the impact of fouling, looking at the effects of their solutions under the foulingreduction light
A Mechanistic Model for the Predictive Maintenance of Heavy-Duty Centrifugal Fans Operating With Dust-Laden Flows
No full textHeavy-duty centrifugal fans are employed for the transport of dust-laden flows in industrial plants, for cement or steel production, or in energy production of plants and mine ventilation systems. These applications require the disposal of huge amounts of suspended particles, which can lead to a gradual erosion of the machine parts where impacts take place. The wear of the fan components can lead to premature failure of the machine, threatening human safety and reliability of the whole plant. The assessment of the wear severity of the machine, according to the process parameters, can aid the plant owner in scheduling overhaul operations along with the operative life of the machine. Moreover, through a reliable estimation of the wear severity, fan manufacturers can optimize the whole machine design process, from the material selection to the warranty time assessment. This work aims to develop a semi-empirical method capable of estimating the erosion severity of centrifugal fans employed for heavy-duty operations. A mechanistic model which accounts for the erosion on the blade leading edge is proposed. The model is derived by means of an analytical approach and accounts for a number of operating parameters (i.e.,, fan geometry, fan operating point, particle concentration in the flow, fluid properties, and material erosion resistance). A comparison of the theoretical model to the computational fluid dynamic (CFD) simulation results obtained through the use of multiphase particle tracking is also provided to assess the reliability of the present method
Dust ingestion in a rotorcraft engine compressor: Experimental and numerical study of the fouling rate
No full textHelicopters often operate in dusty sites, ingesting huge amounts of contaminants during landing, take-off, hover-taxi, and ground operations. In specific locations, the downwash of the rotor may spread soil particles from the ground into the environment and, once ingested by the engine, may stick to the compressor airfoils. In the present work, the Allison 250 C18 engine’s multistage axial-flow compressor is employed to study the fouling rate on rotor blades and stator vanes from both numerical and experimental standpoints. The compressor is operated in a typical ground-idle operation, in terms of the rotational regime and contaminant concentration, in laboratory-controlled conditions. The mass of deposits is collected from the airfoil surfaces at the end of the test and compared to that estimated through the numerical model. The experimental test shows that the airfoils collect almost 1.6% of the engine’s total mass ingested during a ground-idle operation. The capability of numerical methods to predict the fouling rate on the rotating and stationary airfoils of a multistage compressor is tested through the implementation of literature based deposition models. Sticking models show a good agreement in terms of the relative results; nevertheless, an overestimation of the deposited mass predicted is observed
Performance losses and washing recovery of a helicopter engine compressor operating in ground-idle conditions
No full textHelicopters operate often in dusty environments. During landings and takeoffs the engine ingests huge amounts of contaminants that might deposit inside the compressor. In this paper, the ground-idle operation of a helicopter engine compressor has been reproduced on a compressor test unit. The Allison 250 C18 compressor has been subjected to multiple runs under severe conditions of dust ingestion. At the end of each run, the performance curve was recorded while the performance loss has been measured during the operations. Finally, the compressor washing has been carried out and the performance curve has been recorded again. The characteristic curve are representative of the level of contamination of the machine, while the exposure time directly affects the performance loss. The results show the modification and the downward shift of the characteristic curves that lead to a gradual loss of the compressor performance. A detailed photographic report of the first compressor stages has been included in this work. The pictures show the deposition patterns on the blades and the compressor surfaces. The comparison of the pictures of the internal surfaces, before and after the removal of the deposits by the droplet action, highlights the parts that are more critical to clean
Performance Degradation of a Shell-and-Tube Heat Exchanger Due to Tar Deposition
No full textBiomass represents a programmable renewable energy source that is useful for reducing issues related to the transfer from fossil fuels to the renewable energy era. The exploitation of biomass is strongly related to the development of power technologies that are designed to improve efficiency; however, at the same time, they have to be designed to improve the life cycle of the entire installation—especially in relation to maintenance operations. In this paper, a numerical analysis is proposed to assess the performance of a heat exchanger used for separating condensing tar from syngas generated by the gasification of lignocellulosic wood chips and pellets. The analysis included clean, fouled, and clogged conditions. Flow maldistribution characterized the inlet section of shell-and-tube configurations and was responsible for clogging phenomena. Starting from field detection, analyses of fouled and clogged conditions showed a reduction in the effectiveness of the heat exchanger, causing dangerous conditions for the internal combustion engine used to exploit the syngas flow
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