1,720,985 research outputs found
Acoustic Pyrometry Robustness to Time-of-Flight Estimation Errors
No full textAcoustic pyrometry is a widely used technique for contactless temperature measurement. It may be used in several applications, especially when high temperatures and harsh environments are involved. For instance, it has been applied to measure the temperature distribution at gas turbine outlet. This technique is based on the measurement of the time of flight of an acoustic wave through a medium. If multiple emitter-receiver couples are used, using a computational procedure a reconstruction of a temperature map is possible. On the other hand, a full assessment of the robustness of this technique to potential errors in TOF estimation is still missing. In this study, the impact of an inaccuracy in TOF estimation on the reconstruction of a correct temperature map is investigated by means of a statistical approach. As a general result, it was found that when the TOF was measured without inaccuracies, temperature estimation errors may be lowered by simply increasing the number of cells in which the estimation is performed. However, when the estimation of the TOF is affected by errors, an optimal configuration exists that minimize the temperature estimation errors
Measure of the solar flux conveyed onto a lambertian target by a novel bi-axial fresnel concentrator
No full textThis paper deals with the optical analysis of a prototype of a novel concentrator, named as Bi-Axial Fresnel (BAF). This concentrator aims at reducing production and installation costs, as well as keeping as low as possible the weight and the bulk of the mirrors field, making it suitable for building small-dimensions systems, able to be placed on industrial roofs, as an example. The prototype is composed as an array of 3x3 mirrors. Its theoretical concentration is therefore 9. The experiment made use of a very basic equipment, which included a thermal flux sensor and a simple webcam, properly equipped for distinguish grey scales under quite high solar intensities. The concentrator was governed by an Arduino card, while the acquisition took place by means of a National Instruments acquisition board and Labview software. The aim of this experimental setup was the reconstruction of the solar flux on a fixed Lambertian target, based on the grey-scale maps gathered through the webcam and properly scaled accordingly to the punctual solar flux measured by the sensor. This way, the experimental apparatus was able to get an estimation of the solar power conveyed to the target
CFD optimization of CPC solar collectors
No full textThe use of solar energy for industrial purpose at medium-low temperature is receiving attention. As a matter of fact, this temperature range, usually between 80-200°C, requires low cost devices to convert solar energy into useful heat. In particular, the use of CPCs collectors has been suggested in literature because they can be operated without the use of a tracking system, at least within certain limits. The thermal losses of these devices are often reduced by using an evacuated pipe, but this solution increases the manufacturing costs and reduces the reliability and the optical efficiency of the receiver. A series of alternative methods for the thermal losses reduction has been proposed in this paper, for working temperature up to 200°C. Their effectiveness was evaluated by means of a previously validated CFD model. A cylindrical receiver and a concentration ratio of 2 were taken into account. The results were analyzed in terms of temperature contours and thermal efficiency. In particular, the optical efficiency was focused as a key parameter in the performances of a CPC. As conclusion, it was found that a proper arrangement of the absorber with a baffle may entail an improvement of the thermal efficiency without significantly increasing the complexity of the system
Experimental Analysis of Temperature Gradient Effect on Lithium batteries
No full textThis paper investigates the effects of temperature on the behavior of lithium-ion batteries during operation. In particular, we present the results of an experimental analysis aimed at investigating the effect on cell performance of a temperature gradient during the discharge phase. An ad-hoc experimental setup which includes an electronic load, power supply and climate chamber fully controlled through a software interface was developed to test the batteries. The devices under test are subjected to complete charge and discharge cycles at constant temperatures followed by discharge cycles with rising and falling thermal gradients.The effects of a downward (-25 degrees C in 15 min) and upward (+25 degrees C in 15 min) thermal gradient on battery capacity are discussed throughout the paper together with a comparison with constant average temperature discharge profile
Investigation of a 100 μm Magnetic Wire for Temperature Sensing based on a Time Domain Readout
No full textIn this paper we present an analysis of temperature response of a 100 μm hysteretic wire exploiting a time domain readout. The ferromagnetic wire is composed of 80% Co-Fe, 20% Si, B. The study here conducted investigates the effect of temperature in the microwire with an output measured as time response, which represents an intriguing method to convert the target quantity. The experiments have been accomplished by using a MuMetal® electromagnetic shield with controlled temperature and an acquisition system to process the output. Results here reported evince the suitability of the proposed method which arouses interest for several interesting applications
Comparison of Magnetic Field Sensors for Current Distribution Reconstruction through Barycenter Filament Model
No full textIn this paper we compare different magnetic field sensor technologies that can potentially be used to characterize current distribution in massive conductors. The approach is based on the application of the current barycenter method, introduced by the authors in a previous work, to obtain information about the current distribution in massive conductors fed by pulsed current through the use of an array of search loops placed around the conductor. After briefly recalling the method, this paper analyzes the possible use of different magnetic field sensor technologies (search loops, vector and scalar magnetometers) to compare their performance in the use of the current barycenter reconstruction method. The introduced model error as a function of sensor type, conductor cross-sectional shape, and mutual position between sensors and conductor are analyzed and discussed throughout the paper
Detection of Armature-Rail Contact Instabilities in Electromagnetic Launchers
No full textThis article deals with the detection of asymmetrical current distribution and the inspection of the rail-armature contact during the launch operation of electromagnetic rail launchers. The method puts in relationship electromagnetic quantities and geometric distances adopting search loops in symmetric position to the rails and offers an auxiliary geometrical interpretation representing the mutual inductances between each loop and the railgun by equivalent geometrical loci. For this purpose, we provide an analytical description for a case study with infinitely long straight wires, in the quasi-static approximation. An experimental analysis is carried out in static conditions on a railgun prototype available at the University of Pisa for different positions of the armature. Besides, we report an uncertainty analysis of the obtained measurement results, performed via a Monte Carlo simulation. Finally, we extend our analysis to the case of dynamic experiments performed with two different armatures to further validate the proposed approach
Biogas from anaerobic digestion: Power generation or biomethane production?
Full text linkBiogas is a fuel obtained from organic waste fermentation and can be an interesting solution for producing electric energy, heat and fuel. Recently, many European countries have incentivized the production of biomethane to be injected into natural gas grids or compressed and used as biofuel in vehicles. The introduction of an upgrading unit into an existing anaerobic digestion plant to convert biogas to biomethane may have a strong impact on the overall energy balance of the systems. The amount of biomethane produced may be optimized from several points of view (i.e., energy, environmental and economic). In this paper, the mass and energy fluxes of an anaerobic digestion plant were analyzed as a function of the biogas percentage sent to the upgrading system and the amount of biomethane produced. A numerical model of an anaerobic digestion plant was developed by considering an existing case study. The mass and energy balance of the digesters, cogeneration unit, upgrading system and auxiliary boiler were estimated when the amount of produced biomethane was varied. An internal combustion engine was adopted as the cogeneration unit and a CO2 absorption system was assumed for biogas upgrading. Results demonstrated that the energy balance of the plant is strictly dependent on the biomethane production and that an excess of biomethane production makes the plant totally dependent on external energy sources. As for the environmental impact, an optimal level of biomethane production exists that minimizes the emissions of equivalent CO2. However, high biomethane subsides can encourage plant managers to increase biomethane production and thus reduce CO2 savings
Current Distribution in Railgun Rails through Barycenter Filament Model
No full textIn this article, we present a novel measurement method to estimate the current distribution in electromagnetic rail launchers. A loop array is magnetically coupled with the railgun to reconstruct the current barycenter position, from which we can argue on the current distribution through the rail cross section. After describing the adopted measurement procedure, we present the results of an experimental analysis performed using the NGL60 rail launcher at the laboratories of the French-German Research Institute of Saint-Louis (ISL). We also compare the experimental results with finite-element simulations, and we show the agreement during the current pulse transient. Finally, we provide a measurement uncertainty analysis performed using Monte Carlo method
Analysis of Current Ripple effect on Lithium batteries
No full textThis paper investigates the Lithium battery behavior and possible aging effects in presence of current ripple during the operation. In the context of a research funded project aimed at increasing the safety level of Lithium batteries for the naval propulsion, we present the results of an experimental analysis aimed at investigating the effect of current ripple on cell performances. An ad-hoc experimental setup is developed to test the batteries and the effect of current ripple on battery capacity and cell aging is discussed throughout the paper
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