68 research outputs found
Numerical evaluation of heat transfer effects on the improvement of efficiency of a spark ignition engine characterized by cylinder variability
No full textIn this work, the effects of in-cylinder heat transfer on indicated thermal efficiency of a spark ignition engine showing a cylinder-to-cylinder variation are numerically analyzed. A 1D CFD model of engine is developed and integrated with a turbulent combustion sub-model and with a refined thermal sub-model for cylinders and exhaust pipes. The model is validated against the engine measurements. Thermal sub-model includes a Finite Element (FE) approach to predict the temperatures of cylinders and of exhaust pipes. The model correctly reproduces the thermodynamic behavior of cylinders at varying the operating condition. Simulations at low load and speed indicate that in-cylinder heat transfer represents a relevant percentage on total fuel energy entering the cylinder. Therefore, heat transfer exerts an important influence on the improvement of engine indicated thermal efficiency when considering the sole combustion phasing optimization of cylinders and the suppression of cylinder-to-cylinder variation
Influence of Piezo-Driven Synthetic Jet on Water Spray Behavior
No full textThe opportunity of directly managing the spray formation and its characteristics has gained much interest in the last few years, due to the various active flow control methods available nowadays. In this work particle image velocimetry (PIV) has been applied to investigate the effect of a piezo-driven synthetic jet (SJ) on the droplet velocity distribution of a water spray. Tests were carried out under atmospheric conditions within a chamber test rig, equipped with optical accesses, at two injection pressures, namely, 5 and 10 MPa. The SJ orifice axis has been placed 45 deg tilted with respect to the water spray axis, and the nozzle body has been moved along its own axis for three different positions. For each operation condition, the actual influence region of the SJ has been evaluated through a T-test algorithm. The synthetic jet locally interacts with the spray, remarkably energizing the region downstream of the impact. The effectiveness of the actuator decreases for higher injection pressures and shorter distances between spray nozzle and SJ orifice. The study has been corroborated by a vorticity field analysis, which is able to identify the influence of coherent vortex structures generated by the air jet
Experimental characterization of spray water controlled by a synthetic jet
No full textThe paper reports results of an experimental investigation to explore the potential of a synthetic jet (SJ) actuator to control a water spray. Particle Image Velocimetry (PIV) and Phase Doppler Anemometry (PDA) have been applied to characterize, in terms of velocity vector distribution and droplets size, the spray behavior generated by a misting nozzle for humidification under the control of a piezo-element driven synthetic jet. Experiments have been conducted under atmospheric conditions within a chamber test rig equipped with optical accesses, allowing PIV and PDA measurements, and a water misting nozzle driven by a pressure control module. Water has been used as working liquid, investigating the jet action on the water droplets velocity vector distribution and droplets size generated by the nozzle. Tests have been carried out for two injection pressures, namely 5 and 10 MPa. For a certain reference relative position of the SJ orifice, set at 45° with respect to the water nozzle axis, investigation has been performed for three different orifice axial positions and for each operative condition tests have been replicated two-times, with and without the synthetic jet activation. PIV measurements have been taken on 300 realizations and an averaging procedure was applied to provide the velocity vector maps, whereas the number of samples acquired for the PDA tests, performed on different locations, has been set in the order of 105.The two resulting velocity vector maps and the droplets size have been compared and a statistical analysis of the jet effect on the spray velocity magnitude has been carried out. For each operative condition, the influence region of the SJ device on the spray has been computed through a T-Test algorithm. The synthetic jet interacts with the spray locally, energizing the region downstream the impact. The effect of the actuator decreases at higher injection pressures and moving the impact region upwards. Droplets coalescence can be detected along the synthetic jet axis, while no significant variations are observed along the orthogonal direction
Computational fluid dynamics modeling of developing forced laminar convection flow of Al2O3-Water nanofluid in a two-dimensional rectangular section channel
No full textWe propose a numerical analysis of developing forced laminar convection flow of Al2O3-water nanofluid within a two-dimensional rectangular section channel, heated on the top wall with a constant heat flux of 1000 W/m2. The problem is replicated with the finite-element method using Comsol Multiphysics commercial software. Different cases are simulated with Reynolds numbers of 250-1000 and concentrations between 0% and 6% for particle dimensions of 20 and 40 nm. The analysis demonstrates that nanofluids provide better cooling performance with respect to base fluid. We found an increase in average Nusselt number of ∼ 16% for dp = 20 nm and concentration of 6%, whereas an average enhancement of 13% was detected when the particle dimension was 40 nm. On the contrary, a relevant increase in pressure drop occurred when nanofluids were considered
Water spray flow characteristics under synthetic jet driven by a piezoelectric actuator
No full textParticle Image Velocimetry (PIV) and Phase Doppler Anemometry (PDA) have been applied to investigate the droplets size and velocity distribution of a water spray, under the control of a piezo-element driven synthetic jet (SJ). Tests were carried out under atmospheric conditions within a chamber test rig equipped with optical accesses at two injection pressures, namely 5 and 10 MPa, exploring the variation of the main spray parameters caused by the synthetic jet perturbations. The SJ orifice has been placed at 45° with respect to the water spray axis; the nozzle body has been moved on its own axis and three different nozzle quotes were tested. PIV measurements have been averaged on 300 trials whereas about 105 samples have been acquired for the PDA tests. For each operative condition, the influence region of the SJ device on the spray has been computed through a T-Test algorithm. The synthetic jet locally interacts with the spray, energizing the region downstream the impact. The effect of the actuator decreases at higher injection pressures and moving the impact region upwards. Droplets coalescence can be detected along the synthetic jet axis, while no significant variations are observed along a direction orthogonal to it
Numerical investigation on the forced laminar convection heat transfer of Al 2 O 3 -water nanofluid within a three-dimensional asymmetric heated channel
No full textPurpose: The purpose of this paper is to carry out a numerical investigation to study laminar convection flow of Al 2 O 3 -water nanofluids within a three-dimensional rectangular section channel asymmetrically heated. Design/methodology/approach: A three-dimensional model of the channel is designed and simulated by using Comsol Multiphysics. The finite elements method is used to perform the numerical simulation. A variety of cases are taken into account by considering Reynolds numbers ranging from 250 up to 1,000, concentration between 0 and 6 per cent, particle dimension of 20, 40 and 60 nm and inlet temperature equal to 293.15 and 320 K. A constant heat flux of 1,000 W/m 2 is imposed on the top surface of the channel. Findings: The results demonstrate that nanofluids guarantee improved thermal performances with respect to the base fluid, as shown by the augmented Nusselt number. On the other hand, pressure drop shows a noticeable increase; therefore, an entropy generation analysis is developed to establish optimal conditions for the system under investigation. Originality/value: The originality of this work consists in the analysis of a three-dimensional asymmetric heated channel with nanofluids in laminar convection. The present work would be beneficial to improve the design of devices with particular focus on solar thermal panel
QUALITA’ DELL’ARIA NELLE AREE OSPEDALIERE A RISCHIO: CORRELAZIONE TRA FONTI DI INQUINAMENTO, TIPOLOGIA E CONTROLLO DEGLI IMPIANTI DI TRATTAMENTO
No full textEffect of water injection on performance, gas emission and combustion noise of a 2-cylinder Turbocharged SI Engine: experimental and numerical analysis
No full textForecasting energy consumption in the EU residential sector
No full textThe present paper aims to introduce a top down methodology for the forecasting of residential energy demand in four European countries, namely Germany, Italy, Spain, and Lithuania. The methodology employed to develop the estimation is based on econometric techniques. In particular, a logarithmic dynamic linear constant relationship of the consumption is proposed. Demand is estimated as a function of a set of explaining variables, namely heating degree days and gross domestic product per capita. The results confirm that the methodology can be applied to the case of Germany, Italy, and Spain, whereas it is not suitable for Lithuania. The analysis of elasticities of the demand with respect to the gross domestic product per capita shows a negative value for Germany, −0.629, and positive values for Italy, 0.837, and Spain, 0.249. The forecasting of consumption shows that Germany and Italy are more sensitive to weather conditions with respect to Spain and an increase in the demand of 8% and 9% is expected in case of cold climatic conditions
Heat pumps for buildings heating: Energy, environmental, and economic issues
No full textThe present paper analyzes the Italian energy system focusing on the possible energy, environmental, and economic effects that the utilization of individual heat pumps for winter heating can produce. To this aim, a model of the Italian energy system is developed by employing the tool EnergyPLAN in order to develop an hourly simulation of the system at country level. Different scenarios in terms of heat pumps penetration, ranging between 10% and 50%, are simulated and sensitivity analyses in terms of average coefficient of performance of heat pumps are performed. The increase of heat pumps generation shows a steadily decrease of fossil fuel consumption for buildings heating, as well as a reduction of carbon emissions. The utilization of heat pumps for buildings heating leads to an increase of 10 p.p. in the load factor of the combined cycle gas turbine thermal power plants. Furthermore, an optimal heat pumps penetration is determined, namely 20%, which minimizes the energy system costs, calculated as the sum of fuel cost and externalities savings
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