1,721,070 research outputs found
Experimental and numerical assessment of photovoltaic collectors performance dependence on frame size and installation technique
No full textThe performance of a solar photovoltaic silicon panel is inversely proportional to its operating temperature. Therefore the overheating risk must be avoided in order to improve the cells electric efficiency. The temperature increase in a solar cell also gives rise to thermal stresses within the module. In this work the authors propose an experimental and numerical investigation of photovoltaic collectors temperature and efficiency dependence on main design parameters (thickness of the aluminum frame), installation technique (distance between photovoltaic panel and supporting panel, tilt angle of the module), and environmental operating conditions, with particular reference to the wind velocity. Experimental investigations have been conducted on a two photovoltaic modules assembly composed by silicon panels. Numerical simulations have been performed employing a two-dimensional finite element numerical model, validated against experiments carried out by the authors. The validated numerical tool has been applied to evaluate photovoltaic collector performance dependence on panel geometrical parameters, installation procedure and operating conditions. The main objective of the present paper is to provide installation and operating indications in order to maximize efficiency. From the conducted investigations it has been evidenced that an optimal distance of the panel from the support can be found, corresponding to which the efficiency is maximized
Influence parameters on the photovoltaic modules performance
No full textIn this work the authors propose an experimental and numerical investigation of the dependence of temperature and efficiency of photovoltaic modules on main design parameters (thickness of the aluminium frame, etc.), installation technique (distance between photovoltaic panel and supporting panel, tilt angle of the module), and environmental operating conditions, with particular reference to the wind velocity. The main objective of the present paper is to provide installation and operating indications in order to maximize efficiency. From the conducted investigations it has been evidenced that an optimal distance of the panel from the support can be found, in correspondence of which the efficiency is maximized
Influential parameters on ultrafine particle concentration downwind at waste-to-energy plants
No full textA numerical investigation on the parameters influencing the ultrafine particle concentrations downwind an incinerator plant has been carried out on a three-dimensional full scale model. The simulation was based on a modified version of the k-. Îμ turbulence model in order to take into account the thermal buoyancy effect of the plume, and reproducing a stable and neutral atmospheric boundary layer by setting appropriate values of velocity, turbulent kinetic energy and turbulent dissipation rate. The ability of the model to reproduce and maintain a stable atmospheric boundary layer was evaluated by analyzing the turbulent characteristics of the flow along the domain. A parametric analysis made on the basis of different plant operational, environmental, and flue gas treatment parameters was carried out in order to evaluate the impact of incinerator plants on the background concentration of ultrafine particles. The evaluation was made at 5. km downwind the chimney in a breathable area, showing that the most significant impact is due to the flue gas treatment section, with a variation on the background concentration up to 370% for a plant hypothetically working without controls on ultrafine particles emission. Operational and environmental parameters determine variations of the concentrations ranging from 1.62% to 4.48% for the lowest and highest chimney, from 1.41% to 4.52% for the lowest and highest wind speed and from 2.48% to 4.5% for the lowest and highest flue gas velocity, respectively. In addition, plume rise evaluation was carried out as a function of wind speed and flue gas velocity from the chimney
Misura e contabilizzazione dell’energia del gas naturale
No full textIl valore del gas naturale dipende strettamente dall’energia ad esso associata, ovvero dall’energia che potenzialmente è possibile ricavarne attraverso la sua combustione. Per questo motivo l’unica misura (diretta o indiretta) veramente rappresentativa del consumo di gas naturale è quella in energia.
Nel passato, i vincoli tecnologici rendevano tecnicamente realizzabile la sola misura dei volumi di gas nelle condizioni di esercizio (mediante semplici contatori volumetrici) in quanto, in analogia con le reti idriche, il gas di città distribuito era di fatto assimilato ad un fluido incomprimibile. Con lo sviluppo di metanodotti e della connessa distribuzione con reti in pressione la sola misura volumetrica non riusciva più a garantire la possibilità di una misura affidabile, specie nelle utenze di grandi dimensioni e ad elevate pressioni. Solo successivamente sono state sviluppate tecniche adeguate per la misura dei volumi e delle portate istantanee, di norma poi riportate alle condizioni di riferimento (attraverso dispositivi di correzione associati ai misuratori di flusso), per giungere poi alla misura (indiretta) dell’energia attraverso complesse catene di misura costituite da elementi primari, dispositivi di correzione e gascromatografi/analizzatori della qualità del gas. Questi ultimi strumenti, infatti, consentono un’affidabile misura dei principali parametri della qualità del gas o, più semplicemente, consentono di risalire al valore del potere calorifico del gas naturale vettoriato in rete.
Nonostante l’innovazione tecnologica faccia trasparire potenziali futuri sviluppi specie nel campo della miniaturizzazione dei sensori, nelle capacità trasmissive dei segnali di misura e nelle connesse elaborazioni, nella realtà operativa numerosi vincoli gestionali, economici e normativi rendono problematica la misura in energia anche in condizioni impiantistiche e climatiche non particolarmente critiche.
In questo lavoro gli autori, a valle di una breve descrizione delle tecniche di misura disponibili sul mercato nelle installazioni tipiche presenti sulle reti di trasporto, analizzano le principali criticità tecniche e normative connesse alla realizzazione della misura in energia del gas naturale nelle reti distributive nazionali
Artificial compressibility based CBS solutions for double diffusive natural convection in cavities
No full textAnalysis of the operating strategy of a SOFC based unit for thermal and electric residential loads
No full textIn order to bring High Temperature Fuel Cells (HT-FCs) on the market, on-site experiments are crucial to understand HT-FCs based units performance and their actual applicability to residential power generation. The authors present here the results of recent experimental and numerical analysis conducted on a micro-cogenerative Solid Oxide Fuel Cells (SOFCs) based unit. A new measurement system has been designed by the authors on the basis of an a-priori uncertainty analysis, and additional meters have been installed in order to perform an a-posteriori uncertainty analysis. Effective application of HT-FCs to residential use has been studied using the validated numerical model developed by the authors in order to follow electric and thermal loads, and technical and economic analysis have been carried out
A simplified benchmark of ultrafine particle dispersion in idealized urban street canyons: A wind tunnel study
No full textThe paper proposes a benchmark for computational fluid-dynamic models of ultrafine particle (particles' diameter lower than 100nm) dispersion in urban street canyons. In particular, an on-scale symmetric street canyon was designed and settled in a wind tunnel considering a perpendicular wind condition. An experimental campaign was carried out to: i) investigate the fluid-dynamic conditions inside the canyon through a Particle Image Velocimetry (PIV), ii) evaluate the uncertainty budget of the PIV measurements, iii) design proper particle injection and sampling systems in the street canyon not influencing the fluid-dynamic conditions of the canyon itself, iv) provide particle number concentration profiles at different sections of the canyon (at different heights on both the canyon facades and at a background level) through ultrafine particle generation (Submicrometer Aerosol Generator 3940, TSI Inc.) and measuring devices (CPC 3775 and SMPS 3936, TSI Inc.).The study can be considered the very first attempt to set a benchmark for ultrafine particle dispersion in street canyons through wind tunnel systems
MODELING OF THERMAL ENERGY STORAGE: A REVIEW OF DIFFERENT SYSTEMS
No full textIn this paper, different types of Thermal Energy Storage (TES) systems are reviewed and discussed, including sensible heat storage, latent heat storage and aquifer thermal storage. Design criteria, materials selection and numerical models employed have been analysed. The TES systems taken into account are: two types of concentric-tube latent heat systems with Phase Change Material (PCM), a latent heat system employing PCM and metal foam, a packed-bed molten salt thermocline system and an aquifer
A CFD Study on a Calibration System for Contact Temperature Probes
No full textSurface-temperature measurements by means of contact probes require a detailed investigation of the probe-surface interaction. For an accurate calibration of such probes, the heat transfer processes involved in contact measurements must be well known and the impact of any influence parameters must be taken into account. At present, contact probes are generally calibrated by means of a temperature-controlled hot plate. A calibration system for contact surface-temperature probes, based on such a hot plate, was developed at INRIM. It covers the temperature range from ambient to 350 °C. The reference temperature is available on the upper surface of a metal block and is determined by linear extrapolation of the readings of three calibrated thermometers embedded into the block at different depths. However, the actual temperature of the reference surface largely depends on the sensor-to-surface interaction. The contact thermal resistance, the thermal conductivity of the block, the geometry of the probe, and the temperature of the surrounding fluid are just some of the parameters that affect a calibration and that may cause measurement errors if they are not properly taken into account and corrected for. Better insight into the interaction between the surface and the probe is therefore required. Since the experimental evaluation of measurement errors is not straightforward, mathematical modeling could represent a crucial tool to better understand the interactions between the probe and the calibration system. In this paper, a finite-element numerical model of the INRIM calibration system was developed in order to investigate the temperature field across the reference block as well as on its surface during a calibration. The thermal load introduced by a commercial contact probe during a calibration was also included in the simulation and its effect on the temperature field was studied. In order to obtain a detailed mathematical model, the surrounding air was also included in the simulation, avoiding the imposition of boundary conditions at the interface between solid parts and fluid. The proposed model was validated by comparing the results obtained with the available experimental data
Unaccounted for gas in natural gas transport networks
No full textOne of the main issues in the natural gas (NG) transport networks management is represented by the Unaccounted for Gas (UAG). UAG is the quantity to be considered in the balance equation to take into account the unavoidable errors due to measurements and estimations. The resulting problem is twofold: on one hand fiscal and contractual, on the other hand the unavoidable pressure from the national authorities to reduce UAG.
In this paper the authors analyse the UAG trends in natural gas (NG) transport networks and present: i) an investigation about UAG in international networks; ii) a statistical analysis of annual and monthly trends for UAG; iii) the analysis of UAG causes
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