The present paper reports the experimental results and the potential performance of the investigation on flat solar thermal collectors using nanofluids as innovative heat transfer fluids for solar energy applications. The straight use of heat-transfer nanofluids in traditional solar flat panel revealed some technical issues, due to the nanoparticles sedimentation. Therefore, sedimentation has been investigated both in standard solar flat panels and modified ones made from transparent tubes. The results of the first tests showed that the main sedimentation parameter is the flow velocity and to better control it a standard flat panel was modified changing the cross-section of the lower and top header of the panel, that have been tapered to keep constant the fluid axial velocity. The modification of the panel shape (patent pending) enabled a negligible particles deposit. After different nanofluids were tested on the panel prototype, water–Al2O3 was chosen as heat transfer fluid. All tested nanofluids were prepared in batch and their thermal conductivity and convective heat transfer coefficient were measured prior of their use as heat transfer fluid in the solar panel. A thermal conductivity enhancement up to 6.7% at a concentration of 3 vol% was observed, while the convective heat transfer coefficient increased up to 25%.

In the present work a systematic investigation on several mechanisms affecting the thermal conductivity of Alumina based nanofluid, such as layering, Brownian motion, clustering, ballistic phonon motion, thermal boundary resistance and mass difference scattering, is presented. The effect of mass difference scattering is for the first time suggested and studied in the present work. Both theoretical and experi- mental approaches have been carried out in order to analyze the competition of these phenomena and to identify the most relevant. This was obtained by comparing micrometric and nanometric particles suspended in liquid water (293 K), frozen water (253 K) and diathermic oil (293 K). Each of the above- mentioned conditions was selected to make dominant only one of the mechanisms that affect nanofluid thermal conductivity. The main results of this investigation concern the mass difference scattering, which has been found to be the most intensive mechanism reducing the nanofluid thermal conductivity with respect to the microfluid one.

In this paper a critical investigation of layering phenomenon has been carried out, by means of experimental and numerical analyses, to explain the differences in thermal conductivity between nanofluids based on metal (Cu) and metal oxide (CuO) nanoparticles. Particularly, molecular dynamics simulations have been developed to investigate the adsorption of water molecules surrounding Cu and CuO nanoparticles of various sizes. Furthermore, different volume concentrations of nanoparticles in water have been analyzed. The numerical results revealed two shell-like formations of water molecules (layers) close to the Cu nanoparticle surface, differently from CuO nanoparticle, where no significant layering phenomenon has been observed. This result can explain the higher thermal conductivity of Cu-based nanofluid with respect to CuO-based one, which has been experimentally measured. The numerical and experimental results lead to the conclusion that layers of ordered water molecules surrounding metal nanoparticles play an important role in explaining experimental data of nanofluid thermal conductivity.

Il presente lavoro affronta lo studio delle tecniche di produzione di idrogeno, basate su cicli termochimici alimentati da impianti solari a concentrazione ad alta temperatura. In particolare, sulla base dei dati disponibili in letteratura relativi ai componenti costituenti l’impianto, si è sviluppato un modello in grado di produrre idrogeno sulla base del ciclo Zolfo-Iodio (S-I). Ogni componente dell’impianto proposto è stato caratterizzato in funzione dei flussi energetici e di massa e dimensionato in modo da definire le condizioni termodinamiche in ogni punto del sistema. I risultati hanno dimostrato che è possibile realizzare un impianto di produzione di idrogeno da fonte solare avente rendimenti di primo principio superiori al 44%. Inoltre prevedendo il recupero energetico dei cascami termici si è dimostrato che tale rendimento può essere notevolmente migliorato fino a valori prossimi al 65%. I risultati ottenuti rivelano le grandi potenzialità dei cicli termochimici di water-splitting basati sull’utilizzo della fonte rinnovabile solare per un passaggio verso l’economia dell’idrogeno. Il presente lavoro è stato sviluppato nell’ambito del progetto di laboratorio pubblico-privato SOLAR, finanziato dal MIUR.

I collettori parabolici lineari (PTC) costituiscono il tipo più comune di tecnologia solare termodinamica ad alta temperatura (HTST), in cui il fluido di lavoro è di solito olio sintetico o una miscela di sali fusi. Nel presente lavoro è stata svolta l’analisi di un collettore solare ad alta temperatura basato sull’impiego di nanofluido, quale fluido termovettore non convenzionale. A tal proposito, si evidenzia che i nanofluidi possiedono alcune proprietà che li rendono utili in molte applicazioni di trasferimento di calore. In quest’ottica, un'analisi termica ed un algoritmo di calcolo sono stati messi a punto per valutare le prestazioni di PTC, utilizzanti un nanofluido su base gassosa come fluido termovettore.

In this paper, a detailed survey has been carried out in order to evaluate the performance of a micro combined heat and power system, based on internal combustion engine fed with natural gas as prime mover. In particular, several operating modes of the micro combined heat and power system are proposed to satisfy the electric load demand deriving from civil users. These operating modes consider a variable number of users and prime movers, as well as a variable strategy of load sharing among them. Moreover, the analysis takes into account the utilization of an electric energy storage system and a converter allowing the operation of the engine at variable speed as enabling technologies. The comparison has been done using as input a statistical profile of domestic electric load. The results, compared with the performance of the conventional systems, have highlighted a maximum natural gas saving up to 22% with consequent reduction of carbon dioxide emissions. Moreover, the results of simulations show that the number of engines and the engine operation at variable speed determines the greatest benefits on fuel consumption, followed by the utilization of an electric energy storage system. The load sharing strategy, among the operating engines, has, on the contrary, a secondary effect.

In this work, the efficiency of a 1 kWp horizontal-axis wind turbine installed on the roof of the Engineering building at the University of Salento has been evaluated, by means of CFD and experimental data. Particularly the influence of the building on the micro wind turbine performance has been studied and the numerical results (wind velocity fields and turbulence intensity above the building) have been compared with the experimental data collected over a period of time of three years. The results have shown that horizontal axis wind turbines suffer from wake effect due to buildings, therefore best sites in urban area have to be identified by a careful fluid dynamic analysis aimed at evaluating all causes that can reduce significantly the performance of the generator: in fact building should allow to exploit increased wind intensity, but often this advantage is voided by turbulence phenomena, as in the case under investigation where the measured aerogenerator efficiency is lower than the nominal performance curve. Then, the best site can be found by crossing the contours of wind velocity with the turbulence intensity fields: in this way it is possible to localize an area (best location) where the aerogenerator can gives maximum performance.

Cooling of electronic devices is one of the main challenge of new generation technology. The extreme miniaturization has high benefits, but the heat to be dissipated per unit of surface increases in uncontrolled way. In this paper the application of a new generation of heat transfer fluids, nanofluids, to electronic devices is analyzed. Even if the use of nanofluids is not still common, there are many papers that deal with this topic, reporting both experimental and theoretical results. The development of this technology could be one of the key elements that could give an important impulse to further miniaturization of electronic devices and at the same time increase their energy efficiency.

The concept of Oil Stress in a low speed two-stroke Diesel engine has yet to be tackled in the same way or depth as it has been in the four-stroke engine. The present work illustrates a predictive model for cylinder oil stress in low speed two-stroke Diesel engines based on the results from several enginetest campaigns. The experimental investigation has been carried out on Wärtsilä large bore marine diesel engines equipped with several lubrication oil systems and on the Bolnes 3(1) DNL 170/600 research engine from Shell Global Solutions (Germany) GmbH. Acquired experimental data regarded both cylinder oil sampling techniques, chemical and physical laboratory analysis of the oil samples and optical technique to quantify the amount of oil blown off though the inlet ports from the piston ring pack. Relevant differences in used cylinder lube oil properties between samples gathered with different techniques have been found. The paper will describe these findings and will propose an innovative way of looking at oil stress analysis in two-stroke engines.

In urban areas, the evaluation of the energy outcome of a horizontal axis micro wind turbine depends on several factors such as mean wind velocity, location, turbulence, etc. To maximize the micro wind turbine efficiency it is important to define the best location. The present paper focuses on the definition of common rules for micro siting in urban areas. In this work, the efficiency of a 1 kWp horizontal-axis wind turbine has been evaluated, by means of CFD and experimental data. The numerical results have been compared with the experimental data collected over a period of time of three years, by using a measurement equipment installed on the roof of the Engineering building at the University of Salento. The results have shown that horizontal axis wind turbines suffer from wake effect due to buildings, therefore best sites in urban area have to be identified by a careful fluid dynamic analysis aimed at evaluating all causes that can reduce significantly the performance of the generator.

An experimental study on new high temperature parabolic trough collector (PTC), with transparent receiver tube, based on gas-phase nanofluid, has been carried out for the first time in this work. Two-axes solar tracking PTC, with 4 m2 reflecting surface has been realized. Besides, two coaxial quartz tubes, with vacuum in the inner space were used as receiver pipe, with air-dispersed CuO nano-powders as working fluid. The aim of this work was to investigate the technological issues related to the use of gas-based nanofluid coupled with transparent quartz receiver and to evaluate the performance of the first prototype, comparing numerical and experimental results. The experimental campaign highlighted a critical issue related to nanopowder deposition within the receiver pipe, due to humidity. Moreover, in a day of measurement, the fluid temperature higher than 145 °C has been maintained for about 10 h, reaching a maximum value of 180 °C, with a mean efficiency of about 65%.

Global biodiesel production grew by 23% per year between 2005 and 2015, leading to a very strong expansion of the sector in a decade and, at the same time, the interest in the use of liquid biofuels/biodiesel in compression ignition engines has grown quickly. Taking into account that the use of biodiesel in IC engines directly affects their coolant temperature, with impact on performance, in this study an experimental campaign has been carried out on a 4-strokes single cylinder engine, aimed to assess whether the use of nanofluids, instead of water, could be a valuable solution to reduce peak engine temperature. Such nanofluids were characterized by higher thermal conductivity compared to conventional fluids, due to CuO nanoparticles added at different concentrations within the base fluid. Measurements of temperature were recorded at steady and unsteady conditions, by proper thermocouples located around the exhaust valve seat in the cylinder head and in the exhaust valve spindle. Particularly, temperatures of the exhaust valve spindle and exhaust valve seat in the cylinder head were measured at part and full engine loads, using water as coolant and then CuO based nanofluids. Experimental results showed that, at 100% engine load in unsteady conditions, it was possible to achieve a temperature reduction up to 13.6% on the exhaust valve seat and up to 4.1% on the exhaust valve spindle, when nanofluid at 2.5% volume concentration was used.

Nanofluids belong to a new generation of heat transfer fluids. Their thermal properties make them suitable to be employed in high-performance energy systems. In this paper a new setup for investigating the interactions between microwaves and nanofluids is presented. This is a new issue in this field and only one other experimental campaign has been carried out in the scientific world so far. The design of this experimental setup together with the preliminary results on two different water-based nanofluids (Al2O3 and CuO nanofluids) opens a new frontier in the field of heat transfer in nanofluids.

In this study, a modified flat panel solar thermal collector was built and thermal efficiency was measured with two heat transfer fluids: distillated water and Al2O3–distillated water based nanofluid at high concentration (3.0%) volume fraction of solid phase. In this work for the first time nanofluid with high nanoparticle concentration has been used thanks to a modified solar thermal collector, based on patent WO2011138752 A1, which consists in bottom and top headers properly shaped in order to reduce sedimentation of clusters of nanoparticles. Thermal efficiency has been measured through an experimental setup, according to EN 12975-2 standard. Experimental results showed that an increase of thermal efficiency up to 11.7% compared to that measured with water has been obtained by using nanofluid. Besides effect of nanofluid on thermal efficiency is greater at high temperatures.

The work reported in this paper shows experimental results from a study on a new type of heat transfer fluid, nanofluids, using diathermic oil as base fluid. These kinds of heat transfer fluids find application in those areas of heat transfer where high efficiency, compact volumes and high energy fluxes are required. In literature there are not many experimental data on diathermic oil based nanofluids because many experimental campaigns are focused on water nanofluids. On the other hand diathermic oil nanofluids are very important in those applications where high temperatures are reached or where the use of water is not suitable. Samples of nanofluids, with nanoparticles of CuO, Al2O3, ZnO and Cu, having different shapes and concentrations varying from 0.0% up to 3.0%, have been produced and their thermal conductivity has been measured by means of hot-wire technique, according to the standard ASTM D 2717-95. Measurements were carried out to investigate the effects of volume fraction, particle size of nanoparticles and thermal conductivity of base fluid. The effect of temperature has been also investigated in the range 20°C - 60°C. A dependence was observed on the measured parameters and the results showed that the heat transfer performance of diathermic oil enhances more than water with the same nanoparticles.

The efficiency of cooling system is critical for wind turbines, particularly during the hot season, when high temperatures could damage the electric generator and mechanical parts of the turbine. The cooling system proposed in this paper is able to increase the efficiency of heat transfer with the use of nanofluids and the wind turbine tower as a heat exchanger to dissipate waste heat in the environment. In this study the use of Al2O3-water nanofluids has been considered. The results of this investigation appear encouraging because they have shown that the proposed new solution is able to assure highly efficient heat transfer and to limit thermal stresses on the electrical and mechanical components of wind turbines.

An overview of innovations introduced in the field of flat solar thermal collectors is presented using information from different literature sources. Despite the large number of publications available about this specific issue, this review is focused on the last ten years period, to underline the actual trend of the scientific and technologic world so far. Bearing in mind this choice, in this study a selection of the most valuable papers has been done, considering different points of view and aspects. Even if this work cannot be considered exhaustive of the complete literature about this field, it can be taken into account as a quick reference to have an overview about new materials, geometries, heat transfer fluids etc., available and tested in the last decade.

A new model of solar reactor based on a double-loop fluidized bed involving CeO2 nanoparticles and two gas streams, N2 and CO2, for efficient thermochemical fuel production, is presented. The fluidized bed reactors are commonly used to carry out a variety of chemical reactions, due to solid granular materials, which play the fundamental role of catalyst. In the system under investigation, the overall reaction CO2→CO+1⁄2O2 is achieved, by means of a thermochemical two-step cycle, based on CeO2 nanoparticles. The first step (CeO2 thermal reduction) has been implemented with a solar-driven endothermic dissociation of the metal oxide to lower- valence metal-oxide. The second step (CO2 splitting) has been carried out with an exothermic oxidation of the reduced metal-oxide, which is produced in the first step, to form CO. The use of nanoparticles as catalyst allows maximizing the surface area of reaction, and at the same time, the reactor based on double-loop fluidized bed allows continuous operation, without alternating flows of inert sweep gas and CO2. The thermodynamic analysis of the system under investigation showed a calculated maximum ideal efficiency of about 63%.

The Parabolic Trough Collector (PTC) is the most common type of high-temperature solar thermal technology, in which the heat transfer fluid is usually synthetic oil, molten salt or water/steam. Expe- riences in existing plants have shown some operating problems with all these types of fluid, which limit solar to thermal efficiency and increase power plant costs. To solve such constraints an innovative solar Transparent Parabolic Through Collector (TPTC) working with gas-based nanofluid has been proposed and investigated in the present paper. Transparent receivers combined with gas-based nanofluids were found to be able to directly adsorb solar radiation due to the very high total surface of nanoparticles. The use of directly radiated nano- particles allows compensating the relatively low heat transfer coefficient typical of gaseous heat transfer fluids with an increase of the exchange surface. Yet to allow a complete absorption of the solar energy within the transparent receiver tube a proper mixture of CuO and Ni nanoparticles has been designed. The proposed solar collector has been modelled by means of a discretized in space model to simplify the description of the behaviour of the physical system under the assumptions of quasi steady state conditions. The above-mentioned model has then been used to run an optimization procedure to define the main geometrical and operational parameters of the TPTC. Simulations have shown that the maximum TPTC solar to thermal efficiency is 62.5%, for a nanofluid outlet temperature of 650 C and a nanoparticles volume concentration of 0.3%.

In this paper, the design of a double-loop fluidized bed solar reactor, involving CeO2 nanoparticles and two gas streams of N2 and CO2, for efficient thermochemical fuel production, has been optimized in a six-dimensional parameter space by means of a multi-parameter optimization algorithm. The system under investigation is capable to develop a thermochemical two-step cycle, producing CO by means of the overall reaction CO2→CO+1/2O2. The use of nanoparticles as catalyst allows maximizing the performance of the reactor; actually, nanoparticles increase surface area of reaction, with respect to common catalysts and, at the same time, allow realizing the reactor as double-loop fluidized bed, which can operate without alternating flows of CO2 and inert sweep gas. A genetic algorithm coupled with a quasi-random Sobol design population has been used, to find the optimal configuration of the double-loop fluidized bed solar reactor. The results highlighted the very important role of several factors, as radius of fluidized beds, mean residence time of reactor, mass of nanoparticles within reactor, solar concentration ratio, etc., on the performance of the system under investigation and allowed to find the best configuration of the system, reaching the mean global efficiency over a period of time of 1 year equal to 29.96%, with a maximum of 59.46%.

Air conditioning is one of the areas that has a high electrical energy consumption, mainly during summer, in hot and humid climates. The major part of the air conditioning systems are based on the vapor compression cycle, but in the last decades solar cooling technology focused the interest of the scientific community and industrial world. Solar cooling deals with a heat driven cycle for cold production. This technology is well represented by absorption refrigerators and desiccant cooling systems. However, in hot and humid climates the latest cycles are not well developed, therefore the systems based on these cycles cannot face the full cooling load needed by the utilizer. Efforts have to be done in order to change their configuration and improve their efficiency. The aim of this paper is to propose new configurations for solar cooling systems and their adaptation to hot and humid climates.

A numerical method, named WEST (Wind Energy Study of Territory), has been developed and applied to a specific geographical area in south of Italy. This method, through actual historical meteorological and geophysical data of a territory, allows characterizing anemometric fields and, therefore, potential available wind power. WEST has been developed in such a way to be effective in both studies of large area and siting. Particularly, this method is composed by different calculation algorithms, which altogether constitutes the numerical model, which allow obtaining useful information on the technical feasibility of installing wind turbine in an area. In this work, by means of WEST, three-dimensional wind fields of Apulia Region (Italy) have been reconstructed, obtaining the wind power density maps at several heights: 35 m, 60 m, 80 m and 100 m above ground level.

Concentrated solar power (CSP) plants are one of several renewable energy technologies with significant potential to meet a part of our future energy demand. By now, CSP systems are used to supply photovoltaic or thermal power plant, but results on nanorectennas suggest the possibility to use this technology for direct energy conversion of solar radiation into electricity. A rectenna is a rectifying antenna that can be used to directly convert wave energy into DC electricity. Experiences in microwave applications have shown energy conversion efficiency in the order of 85%, and recently empirical tests have demonstrated that this technology can be used up to the infrared wavelength. The present paper, together with first preliminary results on the fabrication of the rectifier (the key element of a rectenna) and its electrical behavior, proposes the numerical simulation of a new CSP system where a receiver, heated by concentrated solar radiation, reemits infrared energy on the nanorectenna, which converts the incoming energy into electricity. In this way the receiver plays the role of a sunlight radiation converter to infrared energy. The numerical simulation of the system consists of two steps. The first is a ray-tracing model to calculate the concentrator optical efficiency and the energy distribution on the focusing area of the parabolic mirror. The second step consists in the receiver temperature calculation as function of the incident solar radiation. The numerical procedure allows the calculation of the concentrator/receiver assembly performance which returns the energy incident on the nanorectenna as a function of external environmental conditions.

Investigations on the potential thermal efficiency of an innovative nanofluid solar thermal collector have been performed using a commercial software (RadTherm ThermoAnalytics rel. 10.5). The Al2O3-nanofluid has been simulated as working fluid of the solar thermal collector, varying the nanoparticles concentration from 0%vol of Al2O3 nanoparticles (pure water) up to 3%vol of Al2O3 of nanoparticles. The numerical model has been validated with experimental data, obtained with a real prototype of the simulated solar thermal collector. Real thermal properties of the nanofluids at different concentrations have been used in the simulations. The boundary conditions used for the simulations have been those of real weather conditions. An increase in thermal efficiency (up to 7.54%) has been calculated using nanofluid with a volume fraction of 3% and the influence of nanoparticles concentration on the thermal performance of the solar collector has been pointed out.

Lubrication of large two stroke marine diesel engines typically is performed by specially blended lubricants with high CaCO3 concentration in order to prevent sulphuric acid corrosion. The feed rate of lubricant, which is injected into the engine, is strictly related to neutralization reaction of sulphuric acid. At the state of the art, its amount is established following a function of engine load and sulphur content of fuel oil, but regardless the stoichiometric quantity needed to neutralize acid corrosion effects. As result of this lubrication strategy, feed rate of lubricant often results higher than the minimum stoichiometric quantity, yielding unnecessary costs, but sometimes feed rate of lubricant and its content of CaCO3 cannot be enough to completely neutralize sulphuric acid, producing corrosion. Taking into account that concentration of CaCO3 within lube oil can be estimated by measuring refractive index, this work aimed to study SPR sensors, capable to measure in real time small variation of lubricant optical properties, in order to adjust lubricant feed rate, according to the real needs of neutralization. Therefore, a numerical optimization of SPR sensors for lube oil characterization has been carried out, analysing several cases, different for laser source, optical prism and thickness of 3 metal film layers. Mathematical results allowed to find the best sensor in terms of sensitivity. This work is the first step towards the development of a semi-closed loop lubrication control system.

This work aims to develop an anaerobic digestion system, which allows recovering energy from olive wastes, solving the problem of their disposal. To reach this result, polyphenols, which are contained in olives inhibiting the digestion process, have to be abated. For this reason a new anaerobic digestion system able to treat the high concentration of polyphenols has been studied. Particularly, this system, composed by a storage of olive pomace, a mixing/washing unit, a pomace/water separation unit (decanter), an ultrafiltration unit and an anaerobic digester, has been numerically investigated to evaluate the anaerobic digestion key variables as a function of the hydraulic retention time (HRT), as well as the production of biogas for different values of the biomass yield factor. The results revealed that by abating polyphenols, the methane potential of the system under investigation rises from 7.5 molCH4/kgTSS to 11.7 molCH4/kgTSS, with an increment of about 56%, for HRT equal to 30 days.

A cost saving procedure for the optimization of a CNG converted diesel engine is proposed. The procedure is performed in five steps. Firstly, a database of different combustion chambers that can be obtained from the original piston is obtained. The chambers in the database differ for the shape of the bowl, the value of the compression ratio, the offset of the bowl and the size of the squish region. In the second step of the procedure, an empirical method is used to extract from the first database, only the combustion chambers able to resist to the mechanical stresses due to the pressure and temperature distribution at full load. For each combination of suitable combustion chamber shape and ignition timing, a CFD simulation is used to evaluate the combustion performance of the engine. Then, an empirical post-processing procedure is used to evaluate the detonation tendency and intensity of each combination. All the tools developed for the application of the method have been linked in the ModeFrontier optimization environment in order to perform the final choice of the combustion chamber. The overall process requires not more of a week of computation on the 4 processor servers considered for the optimization. Moreover, the selected chambers can be obtained from the original piston of the engine. Therefore, the conversion cost of the engine is quite small compared with the case of a completely new piston. The procedure can be applied to diesel engines to be converted to either CNG dedicated or dual fuel combustion. The main aspects and challenges to be taken into account in both cases are also analyzed.

A promising new generation of solar thermal collector able to enhance the thermal efficiency is the DASC (Direct Absorber Solar Collector). In this paper we report optical absorption measurements performed on several water-based nanofluids (Al2O3, CuO, TiO2, ZnO, CeO2, and Fe2O3) as a function of nanoparticles concentration. These measurements are of fundamental importance to assess the possibility to use the above mentioned metal-oxide nanoparticles in liquid-based nanofluids for direct absorption low temperature flat panel solar collector. The obtained results show different optical behaviors of the nanofluids depending on nanoparticles material and concentration. In all measurements the transmittance rises passing from visible to infrared region and in some cases, when the nanoparticles concentration is too low, the extinction distance grows up to values larger than the typical diameter of a solar receiver.

The use of nanofluids as working fluids in direct absorption solar collector is growing up and the study of optical properties of nanoparticles is an important step for the success of this new technology. In this paper we report optical absorption measurements performed on several metal oxide nanoparticles (ZnO, CeO2, Fe2O3) as a function of temperature in the range 25–500 °C, in order to study their optical properties, and to investigate how several heating cycles could affect nanoparticle structural stability and absorption characteristics. These are quite important issues to be investigated in order to assess the possibility to use such metal-oxide nanoparticles as gas-based high temperature nanofluid in Concentrated Solar Power (CSP).

In this paper we report on optical absorption measurements performed on several metal oxide nanoparticles (ZnO, CeO2, Fe2O3) as a function of temperature in the range 25–500 °C, in order to study the optical properties, and to investigate how several heating cycles could affect nanoparticle structural stability and absorption characteristics. These are quite important issues to be investigated in order to assess the possibility to use such metal-oxide nanoparticles as gas-based high temperature nanofluid in concentrated solar power (CSP)

Building integrated-mounted wind turbine (BUWT) is one of the most promising renewable energy devices. However, this renewable energy technology is not fully spread principally due to two factors such as uncertainty in the prediction of wind velocity and high turbulence intensity around the building. In this work, the Taguchi method and the analysis of variance (ANOVA) on a horizontal-axis wind turbine has been applied, to study the influence of geometrical parameters such as building depth, width and height, as well as turbine position on the roof and turbine height. To evaluate the above-cited effects, the airflow around an isolated building of parametrical dimension has been simulated using a Computation Fluid Dynamic (CFD) code calibrated against experimental data in a previous paper from the authors. The results reported in the present paper outline the relative effects of the main building geometrical parameters on the performance of a rooftop installed wind turbine and establish basic guidelines for the optimal location of such turbines.

Il presente lavoro affronta lo studio delle tecniche di produzione di idrogeno, basate su cicli termochimici alimentati da impianti solari a concentrazione ad alta temperatura.

The present work focuses on the development of a Surface Plasmon Resonance (SPR) sensor transducer able to measure lubricant degradation in real time. Preliminary, several simulations were performed, by means of a commercial software (Film Wizard), in order to optimize for the specific application the sensor transducers in term of the proper choice and combination of metal layers material and thickness. In order to realize the sensing transducers, metal thin films were deposited onto SF10 glass slabs by e-beam evaporation. 4 sensing devices have been realized, calibrated and tested. They have been used to acquire the experimental reflectance curves of a new (0 km) and partially used synthetic motor oil (5700 km). Measurements proved that alteration of lubricants, which flow in the SPR sensing device, modifies the signal, which reaches the detector. Therefore, the system can be used to observe in real time oil degradation by the measurement of its optical properties, following the variation in surface plasmon resonance curves. Experimental results showed that all sensors provide good responses, variable within the range of 1%.

The work reported in this paper shows the experimental results from a study on diathermic oil based nanofluids. Diathermic oil finds application in renewable energy, cogeneration and cooling systems. For example, it is used in solar thermodynamic or biomass plants, where high efficiency, compact volumes and high energy fluxes are required. Besides diathermic oil is very important in those applications where high temperatures are reached or where the use of water or vapor is not suitable. Therefore an improvement of diathermic oil thermo-physical properties, by using of nanoparticles, can increase the performance of the systems. In literature there are not many experimental data on diathermic oil based nanofluids because many experimental campaigns are focused on water nanofluids. Samples of nanofluids, with nanoparticles of CuO, Al2O3, ZnO and Cu, having different shapes and concentrations varying from 0.0% up to 3.0%, have been produced and their thermal conductivity has been measured by means of hot-wire technique, according to the standard ASTM D 2717-95. Measurements were carried out to investigate the effects of volume fraction, particle size of nanoparticles on the thermal conductivity of the nanofluid. The effect of temperature has been also investigated in the range 20°C - 60°C. A dependence was observed on the measured parameters and the results showed that the heat transfer performance of diathermic oil enhances more than water with the same nanoparticles.

An analytical overview of experimental results about the heat transfer capabilities of nanofluids is presented, using widely scattered available information from diverse literature sources. It is shown that, despite the large number of publications available about this issue, only few studies provide quantitative estimates on a complete set of experimental conditions so far and many studies are not coherent. Bearing in mind this problem, in this study a selection of the most valuable papers has been done, taking into account different points of view and hypotheses. Even if this work cannot be considered exhaustive of the complete literature in the field of nanofluids, it can be taken into account as a quick reference guide to have an overview of the different heat transfer phenomena in nanofluids and how the most important parameters (size, shape, concentration, materials etc.) influence the expected thermal performance of nanofluids.

Gli impianti solari termodinamici ad alta temperatura sono prevalentemente basati sull’impiego di collettori parabolici lineari (CPL), utilizzanti come fluido di lavoro olio sintetico o una miscela di sali fusi. Solo recentemente è stato avviato lo studio di CPL, impieganti aria come fluido termovettore, con notevoli problemi di carattere tecnologico legati alla concomitanza di elevate pressioni e temperature all’interno dell’impianto. Nel presente lavoro si propone lo sviluppo di un collettore parabolico lineare con ricevitore trasparente in quarzo (CPLT), impiegante, quale fluido termovettore, un nanofluido a base aria. Negli ultimi anni, i nanofluidi sono stati al centro di numerosi studi in ambito nazionale ed internazionale, grazie alle migliorate proprietà di scambio termico (rispetto al fluido base), utili in molte applicazioni di trasferimento di calore. Una proprietà ancora poco esplorata, da un punto di vista applicativo, dei nanofluidi, è quella dell’assorbimento diretto dell’energia solare. Tale principio fisico è alla base del funzionamento del collettore solare oggetto del presente lavoro. Difatti, differentemente dalle soluzioni tecnologiche fino ad oggi esplorate, l’energia solare concentrata sul ricevitore in quarzo trasparente, può essere assorbita direttamente dal nanofluido che scorre al suo interno, incrementando in tal modo le performance di captazione del sistema. Inoltre, rispetto ai primi tentavi di impianti solari termodinamici con fluido termovettore aria, l’impiego del nanofluido consente di incrementare in modo significativo la capacità termica del fluido termovettore, riducendo drasticamente le pressioni di lavoro del sistema. Ciò permette di risolvere parte dei nodi tecnologici ed incrementare i livelli complessivi di sicurezza dell’impianto. In quest’ottica, nel presente lavoro è stato svolto un processo di ottimizzazione dei parametri funzionali di un CPLT (temperature e portate di lavoro, concentrazione di nanoparticelle) raggiungendo un rendimento solare-termico teorico di esercizio pari al 66.74% ad una temperatura di ingresso del nanofluido di 473 K.

Nel presente lavoro si propone lo sviluppo di un collettore parabolico lineare con ricevitore trasparente in quarzo (CPLT), impiegante, quale fluido termovettore, un nanofluido a base aria. In particolare è stato svolto un processo di ottimizzazione dei parametri funzionali di un CPLT (tempera- ture e portate di lavoro, concentrazione di nanoparticelle) raggiungendo un rendimento solare-termico teorico di esercizio pari al 66.74% a una temperatura di ingresso del nanofluido di 473 K.

Lubricant systems are fundamental in engines (automotive, aviation, rail etc.) and in any industrial system where surfaces of moving mechanical parts are in contact [1]. An improper lubrication due to oil degradation over a long period of time can lead to unwanted component failure and increased maintenance costs. Present study, unlike methods developed until now for detecting oil degradation (loss of mechanical, physical, chemical and optical properties) focuses on the development of a Surface Plasmon Resonance (SPR) transduction methodology able to measure lubricant degradation in real time observing the change in the refractive index. This approach answers to environmental regulation and user requirements on performance, lifetime expectancy and engine efficiency

Nanofluids have excellent potentiality in the field of heat transfer fluids and particularly for solar energy systems such as concentrated solar power plants. However they present many issues to be fixed in order to have a large diffusion. One of these is sedimentation. In this paper, stability, viscosity, FT-IR spectra, cluster size and thermal conductivity of Al2O3 – Therminol nanofluids have been investigated as heat transfer fluid in high temperature solar energy systems. Al2O3 – Therminol nanofluids have been prepared to investigate and to improve stability of the suspensions, varying temperature during mixing with magnetic stirrer, amount of surfactant and sonication time with ultrasonic vibrator. Stability of the nanofluid samples was investigated through backscattering technique and for cluster size analysis Dynamic Light Scattering (DLS) was used. Thermal conductivity of the sample was measured in order to evaluate not only the effect of both volume fraction and temperature, but also the influence of the surfactant (oleic acid). Stability of nanofluids depends on temperature during sample preparation and sedimentation phenomenon is inversely proportional to temperature during mixing with magnetic stirrer. Influence of concentration of surfactants was studied through preparation of samples having a solid phase particles concentration of 0.3 %vol, 0.7 %vol and 1.0 %vol, respectively. The presence of surfactants creates some bonds with nanoparticles, which mainly helps nanofluids long-term stability. On the other hand, the presence of surfactants inside the nanofluids does not influence their thermal conductivity. From DLS measurements, a dependence of cluster size on volume fraction was observed for all nanofluid samples. Experimental data show: viscosity increases by increasing volume concentration; nanofluids with and without surfactants show a non-Newtonian behavior and viscosity of nanofluids increases by increasing cluster size.

Obiettivo del lavoro è l’analisi del fenomeno della sedimentazione dei nanofluidi all’interno di pannelli solari piani, finalizzata ad adottare gli accorgimenti necessari alla sua attenuazione o alla sua completa eliminazione. Lo studio è condotto su pannelli a tubi trasparenti attraverso analisi ottica. In una fase iniziale si è realizzato un pannello solare piano a tubi trasparenti, con le dimensioni di un classico pannello disponibile in commercio, all’interno del quale si è fatto fluire un nanofluido a base di acqua e ossido di alluminio (Al2O3). Le zone interessate dalla sedimentazione della fase solida erano il tubo collettore di ingresso, quello collettore di uscita e i tubi traversi La quantità di fase solida depositata è risultata essere dipendente dalla velocità del nanofluido nei tubi di ingresso e di uscita. Nella fase successiva si è realizzato un pannello solare piano, delle stesse dimensioni del precedente, con una modifica sui tubi di ingresso e di uscita, volta a eliminare il fenomeno della sedimentazione per effetto di una opportuna variazione di velocità del nanofluido. La forma era tale da garantire una velocità costante lungo tutta la loro lunghezza. Essa è stata ottenuta agendo sulla sezione di passaggio all’interno dei tubi attraverso l’introduzione di un solido opportunamente sagomato. Il nanofluido utilizzato era a base di acqua e Al2O3 ed era alimentato nelle stesse condizioni adottate per il pannello della prima fase. Per effetto delle modifiche apportate il fenomeno di sedimentazione si è ridotto a livelli trascurabili e, in certi punti, è stato completamente eliminato. Il pannello solare modificato, dotato di tubi a sezione variabile, è stato oggetto di domanda di brevetto per invenzione industriale depositata all’Ufficio Italiano Brevetti e Marchi (N° LE2010A000006) e successivamente è stata depositata anche la domanda di brevetto internazionale (Application number: PCT/IB2011/051988).

Le pompe di calore geotermiche hanno avuto in Italia nell’ultimo decennio sviluppo e diffusione grazie soprattutto al fatto che consentono consistenti risparmi energetici quando utilizzate per soddisfare il fabbisogno di climatizzazione estiva e invernale degli edifici. In questo lavoro vengono analizzati i diversi modelli matematici presenti in letteratura per il calcolo delle prestazioni delle pompe di calore dotate di scambiatori orizzontali e verticali e per le relative metodologie di dimensionamento semplificate. A seguito dei risultati di questa analisi è stato concepito e implementato un modello matematico in ambiente Matlab-Simulink che integra le metodologie per la progettazione dei sistemi geotermici verticali e orizzontali e valuta le potenze termiche scambiate con il terreno correggendo i valori tabellari di riferimento e largamente in uso nella progettazione semplificata degli impianti di piccola taglia, in funzione delle particolari condizioni operative. Il modello è tarato con il riferimento a risultati sperimentali e ai valori in uscita dalle procedure di calcolo del software RETScreen.

Solar concentration system with thermo-vector fluid made up of gas-based nanofluids and with suitably shaped receiver element of the solar radiation.

Nanofluid comprising bi-distilled water, copper oxide nanoparticles having average dimension between 5 and 10 nm and ionic surfactant. The copper oxide particles volume percentage with respect to the nanofluid is between 1% and 4%. The mass ratio between the surfactant quantity present in the liquid phase and the quantity of nanopowders is between 0,1% and 1.2%.

The present invention relates to a device based on the Surface Plasmon Resonance technique (SPR) for the accurate and in real time diagnostics of the characteristics of the fuel and/or lubricant in internal combustion engines.

Object of the present invention is a new nanorectenna based device for high efficiency conversion of sunlight in electric energy to be used for example in solar concentrators.

New Graeztel cell (or DSSC: dye-sensitized solar cell) provided with a refilling system both of the electrolyte and the organic dye (dye).

Solar concentration system with thermo-vector fluid made up of nanofluids and with suitably shaped receiver element of the solar radiation.

Method for the production of nanoparticles of metallic oxides comprising the steps of stirring the chemical reactants needed in liquid or solid phase; increasing pressure and temperature of the solution; adding a chemical reactant which favours the formation of nanoplarticles; centrifugation of the solid-liquid bi-phase solution containing the nanoparticles of dispersed metallic oxide; washing, drying and storage of the nanoparticles. Plant for the production of nanoparticles according to the described method.

Solar collector for applications with nanofluids or biphasic heat transfer fluids, including both a top pipe ( 1CT) and a bottom pipe ( 1CB ) wherein at least one of these pipes has a variable cross section in order to avoid sedimentation of nanofluids and other biphasic heat transfer fluids that flow inside the tubes of the solar collector itself.