Cristina Cornaro

Flow visualization of a round jet impinging on cylindrical surfaces

Abstract Smoke wire flow visualization is used to investigate the behavior of a round jet issuing from a straight tube and impinging on concave and convex surfaces with high relative curvature values. Local velocity and turbulence intensity measurements of the free jet are correlated to the formation of the visualized ordered-flow structures. Visualization of the impinging jet shows the initiation and growth of ring vortices in the jet shear layer and their interaction with the cylindrical surfaces. Effects of relative curvature, nozzle diameter, nozzle-to-surface distance and Reynolds number on the jet flow structure are described.

Neural Networks and Support Vector Machine Algorithms for Automatic Cloud Classification of Whole-Sky Ground-Based Images

Clouds are one of the most important meteorological phenomena affecting the Earth radiation balance. The increasing development of whole-sky images enables temporal and spatial high-resolution sky observations and provides the possibility to understand and quantify cloud effects more accurately. In this letter, an attempt has been made to examine the machine learning [multilayer perceptron (MLP) neural networks and support vector machine (SVM)] capabilities for automatic cloud detection in whole-sky images. The approaches have been tested on a significant number of whole-sky images (containing a variety of cloud overages in different seasons and at different daytimes) from Vigna di Valle and Tor Vergata test sites, located near Rome. The pixel values of red, green, and blue bands of the images have been used as inputs of the mentioned models, while the outputs provided classified pixels in terms of cloud coverage or others (cloud-free pixels and sun). For the test data set, the overall accuracies of 95.07%, with a standard deviation of 3.37, and 93.66%, with a standard deviation of 4.45, have been obtained from MLP neural networks and SVM models, respectively. Although the two approaches generally generate similar accuracies, the MLP neural networks gave a better performance in some specific cases where the SVM generates poor accuracy.

Jet impingement cooling of a convex semi-cylindrical surface

Liquid crystals are used to investigate the effect of high relative curvature on surface heat transfer for a round air jet impinging perpendicularly on a semicylindrical convex surface.The relative curvature, ( d/D), is varied by changing the jet tube diameter for the same surface diameter. Relative curvature varies from 0.18-0.38. The effects of relative curvature, Reynolds number and jet exit-to-surface spacing are described.  2001 Editions scientifiques et medicales Elsevier SAS jets / jet impingement / curved surfaces / impingement heat transfer / liquid crystals

Outdoor ESTER test facility for advanced technologies PV modules

In the paper the new outdoor test facility ESTER (Solar Energy TEst and Research) for PV modules of various technologies is presented. The facility has been partially funded by the Regione Lazio, Italy, in the framework of the Centre for Hybrid and Organic Solar Energy (CHOSE). This structure is intended to give support to the improvement of reliable and durable organic photovoltaic cells and modules and could offer, in the near future, quality assurance and possible calibration services for PV modules of other technologies. The facility has been designed and built in order to fulfil some of the requirements of the European standards IEC 61215, IEC 61646 and of IEC 60904-1and IEC 61829. Characterization of the climatic conditions of the Tor Vergata site on a three years data basis is also presented, proving Tor Vergata to be a suitable site for PV monitoring and test.

The temperature sensor on the Huygens probe for the Cassini mission: design, manufacture, calibration and tests of the laboratory prototype

Abstract A platinum resistance thermemeter will be used to determine the vertical temperature profile of the Titan lower atmosphere. The sensor is part of the HASI (Huygens Atmospheric Structure Instrument) which will be located on the Huygens probe for the Cassini mission. The design and manufacture of a laboratory prototype have made it possible to verify calibration and test procedures appropriate to the flight units. The sensor has been selected and evaluated with great care in order to ensure performance within the mission requirements which demand accuracy and resolution of 0.5 and 0.02 K, respectively. The calibration and test results confirm performance within the design goals. Further results, dealing with mechanical characterizations aimed at verifying the sensors capability to withstand launch, entry and descent conditions, are also presented.

Monitoring Indoor Carbon Dioxide Concentration and Effectiveness of Natural Trickle Ventilation in a Middle School in Rome

An extensive CO2 concentration monitoring activity was carried out in a middle school located in Rome. Objective of the study was to evaluate the indoor air quality in eight classrooms during class occupation and to evaluate the ventilation rates of a natural trickle ventilation system, through an interactive approach involving the pupils. The analysis was conducted in two phases: a long-term analysis that consisted of evaluating the CO2 concentration and indoor air temperature in each classroom during the 2009/2010 scholastic year to obtain a snapshot of the indoor environment and a short-term testing carried out in 4 days in February 2010, involving the pupils in the monitoring activity. The campaign was performed during the teaching hours and students registered the air exchange events (opening and closing of windows and door) during the class hours. The correlation of the air exchange events recorded by the students with the CO2 concentration level recorded every minute and the opening and closing control of the trickle ventilation system allowed the evaluation of the ventilation rate of the system. The interactive evaluation approach gave the conclusion that the system alone could not completely fulfil its performance requirement.

Deterministic and Stochastic Approaches for Day-Ahead Solar Power Forecasting

Photovoltaic (PV) power forecasting has the potential to mitigate some of effects of resource variability caused by high solar power penetration into the electricity grid. Two main methods are currently used for PV power generation forecast: (i) a deterministic approach that uses physics-based models requiring detailed PV plant information and (ii) a data-driven approach based on statistical or stochastic machine learning techniques needing historical power measurements. The main goal of this work is to analyze the accuracy of these different approaches. Deterministic and stochastic models for dayahead PV generation forecast were developed, and a detailed error analysis was performed. Four years of site measurements were used to train and test the models. Numerical weather prediction (NWP) data generated by the weather research and forecasting (WRF) model were used as input. Additionally, a new parameter, the clear sky performance index, is defined. This index is equivalent to the clear sky index for PV power generation forecast, and it is here used in conjunction to the stochastic and persistence models. The stochastic model not only was able to correct NWP bias errors but it also provided a better irradiance transposition on the PV plane. The deterministic and stochastic models yield day-ahead forecast skills with respect to persistence of 35% and 39%, respectively.

The impact of outdoor meteorological parameters on the performance of dye-sensitized solar cells

The paper presents a first study of the impact of meteorological parameters on outdoor performance of DSC. A DSC cell has been tested in real operating conditions while located in the University of Rome Tor Vergata ESTER outdoor facility, where global, direct, diffuse and reflected solar radiation, air and cell temperature, wind speed and direction, humidity are continuously monitored.

Comparative Analysis of Crystalline and Double-Junction Amorphous Silicon Modules Performance in Outdoor Conditions

The paper deals with an extensive photovoltaic (PV) modules monitoring activity carried out at the outdoor station ESTER (Solar Energy TEst and Research) of the University of Rome Tor Vergata, Italy. The purpose of the work was to evaluate and compare the performance of PV silicon modules of polycrystalline (poli-Si) and amorphous (a-Si) technologies during a medium-term outdoor exposure at optimized tilt angle, facing south. Two PV modules, one polycrystalline silicon and one double-junction amorphous silicon, have been exposed since May 2009 until Oct. 2010. A complete characterization of the weather conditions at the site during the test has been performed, and the most relevant parameters for the performance comparison of the two technologies have been derived. In order to compare different technologies and power productions, the energy yield (Y) and performance ratio (PR) for the two modules have been evaluated on a monthly and yearly basis. The typical seasonal trend of PR has been observed for the polycrystalline module, essentially due to the temperature influence on the module performance. For the a-Si module, instead, a degradation trend has been observed for the first months of operation. Subsequently, a significant recovery in the PR and energy production has been registered.

Organic Photovoltaics for Energy Efficiency in Buildings

Organic photovoltaics is now reaching a more mature stage and new applications are emerging to its direct use as active elements into buildings. This chapter illustrates the more recent developments of organic photovoltaic technology focussing on the description of semitransparent devices integrated into glazing systems for energy efficiency in buildings. It describes briefly the fundamental functioning principles of Hybrid and Organic (HOPV) devices that includes Dye Sensitized Solar Cells (DSC), polymeric cells as well as new emerging technologies, followed by a description of the actual studies carried on building integrated HOPV. Last section presents some showcases of HOPV integrated into buildings.