| 24871. |
- Manjate, Juvencio Arnaldo, et al.
(författare)
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Can Energy-Aware Routing Improve the Energy Savings of Energy-Efficient Ethernet?
- 2018
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Ingår i: IEEE Transactions on Green Communications and Networking. - : Institute of Electrical and Electronics Engineers (IEEE). - 2473-2400. ; 2:3, s. 787-794
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Tidskriftsartikel (refereegranskat)abstract
- Telecommunication networks are over-provisioned with redundant resources in order to cope with traffic load during peak hours and to quickly recover from failures. However, much of the resources are underutilized during long periods of time, but still consuming full energy. With the growing concerns of energy waste and greenhouse gas emissions, the network design principles tend to shift towards allocation of resources on-demand for energy-efficiency. In this paper, we analyze and evaluate the performance of two different energy-saving techniques, namely energy saving topology control (ESTOP) and energy-efficient Ethernet (EEE). We investigate the energy-saving characteristics of ESTOP+EEE; the combination of ESTOP and EEE. The evaluation is conducted in OMNet++ with realistic and synthetic network topologies under varying traffic conditions. The results indicate that the combination has a significant potential for saving energy, compared to running ESTOP or EEE alone, but that the amount of energy savings depends on topology, traffic load, and the chosen target connectivity level for ESTOP. In particular, the results show that the target connectivity level needs to be carefully matched to the topology and the current traffic situation, suggesting that ESTOP+EEE would be suitable where the target connectivity level is dynamically adjusted according to traffic variations.
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| 24872. |
- Manjunath, Manjunath, et al.
(författare)
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Experimental Analysis of Rolling Torque and Thermal Inlet Shear Heating in Tapered Roller Bearings
- 2023
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Ingår i: Machines. - : MDPI AG. - 2075-1702. ; 11:8
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Tidskriftsartikel (refereegranskat)abstract
- The investigation in this article focuses on the rolling resistance torque and thermal inlet shear factor in tapered roller bearings (TRBs) through systematic experiments using a modular test setup. TRBs typically operate under Elastohydrodynamic Lubrication (EHL) conditions. At sufficiently high speeds, the majority of rolling friction is due to a significant shift of the pressure centre in the EHL contact. While at lower speeds, sliding friction in the roller-rib contact becomes dominant, which operates under mixed lubrication conditions. Limited literature exists on the impact of inlet shear heating on effective lubricant temperature ((Formula presented.)) and rolling friction in TRBs. To fill this gap, experimental measurements of the total frictional torque under axial loading at different speeds and oil temperatures are performed. With existing models for different friction contributions described in the literature, the rolling resistance due to EHL has been determined for various operating conditions. The effects of dimension-less speed (U), material (G), and load (W) parameters have also been investigated. Under fully flooded conditions, it was observed that the influence of material (G) and load (W) parameters on rolling friction is minor, while the impact of velocity (U) is significant. In the context of rolling resistance, the heating due to shear of the lubricant in the inlet zone plays a significant role. For higher rotational velocities, the estimated rotational torque reduction resulting from inlet shear heating was found to be approximately 6–8%.
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| 24873. |
- Mann, B. S., et al.
(författare)
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High temperature friction and wear characteristics of various coating materials for steam valve spindle application
- 2000
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 240:1-2, s. 223-230
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Tidskriftsartikel (refereegranskat)abstract
- Various coatings such as chromium carbide (deposited by plasma spraying and detonation gun techniques), chromium oxide, chromium oxide + titania + silica, NiCrAlY, and Al2O3 + Ni all deposited by plasma spraying; stelliting, and surface nitriding have been applied on X20CrMo V121 steel. This steel is used for high temperature applications such as steam turbine valve spindle. Friction and wear behavior of the surface coated and treated materials have been studied at an elevated temperature of 550°C while rubbing against graphite-filled stellited steel. These studies have been carried out on SRV optimol reciprocating tribometer. Test parameters for tribological studies have been selected with a view to simulate operating conditions encountered in operation. Additionally, the structure, porosity, hardness, bond strength, and thermal cycling behaviour of these surface coated/treated materials have been characterised. Based on these laboratory investigations, chromium carbide coating deposited by plasma spraying technique has been identified as the most suitable coating for steam turbine valve spindle application. Process parameters have been established for deposition of chromium carbide coating by plasma spraying technique on actual valve spindles. The field results obtained are found to be commensurate with the laboratory findings.
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| 24874. |
- Mannazhi, Manu, et al.
(författare)
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Influence of potassium chloride on PAH concentration during soot formation studied using laser-induced fluorescence
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 235
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have shown that addition of potassium chloride (KCl) reduces soot concentration and primary particle size. To improve the understanding of this phenomenon, this work focuses on investigating the influence of KCl addition on formation of polycyclic aromatic hydrocarbons (PAHs), assumed to be precursors of soot. The method used is laser-induced fluorescence (LIF), for which different size classes of PAHs can be probed using selected combinations of excitation and detection wavelengths. KCl solutions of different concentrations were aspirated into premixed ethylene-air flames, and spectral and 2D imaging PAH-LIF measurements were performed using laser excitation at 266 nm and 532 nm. PAH-LIF spectra using 266 nm excitation showed a peak in the UV region at around 350 nm and a peak at around 550 nm in visible region, where the latter peak intensity increased strongly with flame height. The normalised PAH-LIF spectra obtained using 532 nm excitation showed no spectral change with flame height. The main results from this study showed that KCl addition, firstly, had negligible influence on the formation of smaller PAHs (measured using excitation at 266 nm and detection at ∼ 320 nm), and secondly, decreased the formation of larger PAHs at increasing flame heights (measured using excitation at 532 nm and detection in the visible region).
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| 24875. |
- Mannazhi, Manu, et al.
(författare)
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Laser-induced fluorescence for studying the influence of potassium and sodium salts on PAH formation in sooting premixed flames
- 2022
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Ingår i: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 128:4
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have shown that alkali salts influence combustion processes and soot formation, although the effects seem to vary across systems. Moreover, fundamental studies on the effect of potassium and sodium salts on formation of polycyclic aromatic hydrocarbons (PAH), which are precursors in soot formation, are scarce. Here, we report a study in which the effects on PAH formation due to the addition of alkali metal salts (KCl, KOH, K2CO3, NaCl and NaOH) to premixed ethylene–air flames were investigated. Different size classes of PAHs were probed using both spectral and 2D measurements of laser-induced fluorescence (PAH-LIF) using the excitation wavelengths 266 nm and 532 nm, while detecting the fluorescence emission at selected wavelength ranges. Elastic light scattering (ELS) measurements were also used to complement the fluorescence data. It was found that potassium and sodium salts do not significantly influence the formation of small PAHs (2–3 rings), while decreasing the concentration of larger PAHs at higher heights above burner (HAB). Another important result was that the anion in the salt (Cl−, OH−, CO32−) negligibly influences the PAH and soot formation processes after dissociation of the salts.
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| 24876. |
- Manova, S., et al.
(författare)
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Experimental investigation of heat transfer characteristics in a miniature flat heat pipe with multi-channels
- 2024
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier Ltd. - 0017-9310 .- 1879-2189. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- The heat transfer characteristics of a miniatured flat heat pipe (MFHP) with multi-channels, featuring a port diameter of 1.18 mm, is investigated experimentally. Various operating parameters are considered, including the working fluid volume (Vf = 1.5, 2.5, and 3.5 ml), length of the liquid reservoir (Lres = No reservoir, 5, and 10 mm), orientation such as axial face (αa) or lateral side (αl), inclination angles (α = −15 to 90o), and cooling water flow rates (ṁi = 10, 15, and 20 LPH). Based on the experiments, the optimal values for the working fluid volume, reservoir length, and flow rate are determined as Vf = 2.5 ml, Lres = 5 mm, and ṁi = 20 LPH, respectively. Further analysis reveals that, the heat dissipation rate for the axial face is significantly higher than that of the lateral side, with an average percentage increase of 35.4 %. However, the lateral side outperforms the axial face in terms of stabilizing the evaporator wall temperature, reducing fluctuations by an average of 24.5 %. Moreover, the presence of multi-channels allows the MFHP in axial face orientation to dissipate a maximum heat load of 15 W against gravity at an inclination angle of αa = −15o. Finally, the variations in MFHP operation based on the orientation and its underlying physical mechanisms that contribute to enhancing heat transfer are discussed.
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| 24877. |
- Manrique Carrera, Arturo, 1974-
(författare)
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Catalytic Combustion in Gas Turbines : Experimental Study on Gasified Biomass Utilization
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Environmental and geopolitical concerns encourage societies towards the utilization of renewable energy sources (RES). Photovoltaic and wind power can produce electricity directly, although their intermittent characteristic negatively affects the security and safety of the energy supply chain; moreover, in order to be viable it is necessary to establish energy storage systems and to find mechanisms to adapt the power distribution grid to larger production variability. In contrast, biomass (a carbon neutral fuel if adequately managed) can be stored, is relatively widely available, and after simple treatments can be gasified and ready to be used for power production. Correspondingly, gas turbines are a well-established technology that first became relevant in industrial applications and power production since 1940’s. The use of biomass in gas turbines is an important step forward towards more sustainable power production; however, this combination presents some technical challenges that have yet to be overcome.Gasified biomass is generally a gas with low or medium heating value that is usually composed of a mixture of gases such as CO, H2, CH4, CO2, and N2 as well as other c60*6nents in small fractions. Its firing in standard gas turbine combustors might be unstable at certain load conditions. Moreover, gasified biomass contains undesirable compounds; in particular the nitrogen-containing compounds that may produce elevated NOx emissions once the biomass is burned.Catalytic combustion is an alternative for using gasified biomass in a gas turbine, and it is investigated in this study. Using catalytic combustion is possible to burn such a mixture of gases under very lean conditions, extending the normal flammability limits, reducing the maximum temperature of the reaction zone, and thus reducing the thermal NOx formation. It also reduces the vibration levels, and it is possible to avoid fuel-NOx formation using alternative catalytic techniques, such as Selective Catalytic Oxidation (SCO).In the present study the feasibility of using catalytic combustion in a gas turbine combustor is evaluated. The tests performed indicate the necessity of using hybrid combustion chamber concepts to achieve turbine inlet temperatures levels of modern gas turbines. The different catalytic burning characteristic of H2, CO and CH4 was evaluated and different techniques were applied to equalize their burning behaviour such as the diffusion barrier, and partially coated catalyst. Fuel-NOx is another subject treated in this work, where a Selective Catalytic Oxidation (SCO) technique is applied reaching up to 42% of fuel NOx reduction. Finally, the use of Catalytic Partial Oxidation (CPO) of methane was experimentally investigated.In this study, two one-of-a-kind test facilities were used directly, namely the high-pressure test facility and the pilot scale test facility. This gives a unique characteristic to the study performed. Finally, the catalytic combustion approach allows the utilization of gasified biomass with some restrictions depending on whether it is a Catalytic Lean, Catalytic Rich or Catalytic Partial Oxidation (CPO) approach.
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| 24878. |
- Mansi, Ghada, et al.
(författare)
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Design of COTS Vertical Axis Wind Turbine for Urban Areas
- 2018
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Ingår i: Proceedings - 2018 International Conference on Promising Electronic Technologies, ICPET 2018. - : IEEE. - 9781538656976 ; , s. 69-73
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Konferensbidrag (refereegranskat)abstract
- In this paper we describe the design of a vertical axis wind turbine (VAWT) that fits residential areas. Such turbines are needed in regions with dense population such as Gaza Strip where the majority of the population are living in urban areas and they seek to reach energy self-sufficient buildings due to the severe electricity shortage in the local grid. The main consideration for a VAWT wind turbine to be suitable for urban areas is the safety factor. Another consideration is being able to turn and produce electricity at low wind speeds. Those two factors will shape the design of the VAWT wind turbine. The designed wind turbine should be compact enough to be installed on rooftops. A target power rating of 5 k Watt is set for the wind turbine as a considerable amount of power to supply a typical residential home. The efficiency of the designed wind turbine is validated experimentally by the recorded wind speeds from an anemometer and the estimated harvested power from the turbine itself. Further schemes and modifications on the design are suggested for improving the power efficiency.
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| 24879. |
- Mansouri, M., et al.
(författare)
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Thermal and dynamic characterization of wet clutch engagement with provision for drive torque
- 2001
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 123:2, s. 213-224
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Tidskriftsartikel (refereegranskat)abstract
- Wet clutches that handle the gearshifts in automatic transmission undergo severe thermal stresses due to the occurrence of large temperature gradients during engagement. To accurately design wet clutches, better models to simulate the engagement process are needed. This work presents a finite element model for simulating wet clutch engagements. The total friction coefficient was used to describe the different lubrication regimes that a wet clutch engagement undergoes. The model also includes provision for drive torque that realistically simulates the engine torque of a car. The results of the simulations are successfully verified by comparison with laboratory experiments on a testrig specially designed to accommodate the drive torque, covering a wide range of typical engagements. Excellent agreement between experiment and simulations is reported in terms of both the dynamics of the engagement and the thermal characteristics. The results are indicative of the utility of the model as a useful engineering tool.
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| 24880. |
- Mantel, Luca, et al.
(författare)
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A Degradation Diagnosis Method for Gas Turbine-Fuel Cell Hybrid Systems Using Bayesian Networks
- 2021
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Ingår i: Journal of engineering for gas turbines and power. - : ASME. - 0742-4795 .- 1528-8919. ; 143:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims to develop and test Bayesian belief network-based diagnosis methods, which can be used to predict the most likely degradation levels of turbine, compressor, and fuel cell (FC) in a hybrid system based on different sensors measurements. The capability of the diagnosis systems to understand if an abnormal measurement is caused by a component degradation or by a sensor fault is also investigated. The data used both to train and to test the networks are generated from a deterministic model and later modified to consider noise or bias in the sensors. The application of Bayesian belief networks (BBNs) to fuel cell-gas turbine hybrid systems is novel, thus the results obtained from this analysis could be a significant starting point to understand their potential. The diagnosis systems developed for this work provide essential information regarding levels of degradation and presence of faults in a gas turbine, fuel cell and sensors in a fuel cell-gas turbine hybrid system. The Bayesian belief networks proved to have a good level of accuracy for all the scenarios considered, regarding both steady-state and transient operations. This analysis also suggests that in the future a Bayesian belief network could be integrated with the control system to achieve safer and more efficient operations of these plants.
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