1,720,987 research outputs found
Performance Evaluations of Steam Power Plants with Dry Cooling Towers
No full textA theoretical model is presented to design dry cooling tower systems and to evaluate their off-design performances. The influence of the more important design parameters on the tower dimensions is shown. A preliminary optimum size is predicted by means of a computer code using a simplified cost model. Moreover, the influence of the designed cooling system on the performance of thermoelectric and/or nuclear power plants is analyzed. The study of the performance of air heat exchangers with plastic tubes (e. g. high-density polyethylene) and of wet and dry-wet cooling systems, as well as a deeper economical cost analysis represent the natural development of this research
Power generation in externally fired air turbine feed by biomass derived syngas
No full textIn a context where the depletion of traditional energy sources together with the emission reduction question reached a dead end, increasing attention is posed towards emerging technologies. Among such technologies, those for which energy is produced locally by residual biomass have gained in the last decades a role of first relevance. Today, different technologies can be successfully applied for distributed energy production from biomass. Gasification is the most promising because offers the possibility to achieve the highest net efficiency. Nevertheless, several questions need to be addressed to get this technology ready to market. The major drawback is related to the presence, in the produced gas, of tars and condensables that still greatly inhibits the application of this technology. The most common configuration for small scale applications is that where the syngas produced in a downdraft gasifier is feed, after its purification, in an internal combustion engine (ICE) for power production. In this work, a new configuration where syngas produced by downdraft gasifier is feed directly in an externally fired air turbine is discussed and numerically analysed. A numerical model of the whole process was built using an in-house code and results were evaluated in terms of first law efficiency. © 2018 AMSE Press. All rights reserved
A Quasi-dimensional Numerical Investigation of the Scroll Expander of an Organic Rankine Cycle Unit
Full text linkScroll compressors are often used in air conditioning and refrigeration systems thanks to their high efficiency, low noise and vibrations, light weight and high reliability. Scrolls are also widely used as positive displacement expanders in small-scale power generation systems, such as Organic Rankine Cycles (ORCs). In recent years, the research has focused on the development of mathematical models that help to predict the scroll expander performances under different operating conditions. In this work, a quasi-dimensional model of a scroll expander of an Organic Rankine Cycle unit is presented. Such an expander consists of two identical circle involute spirals, with appropriate starting segments. Specifically, the model is able to design the scroll expander geometry with either a "circular cutter"or a "perfect mesh profile"(PMP) approach, which are two of the most common scroll geometry starting segments. As regards the thermo-fluid dynamic aspects, specific sub-models have been used to account for radial and axial leakage, wall heat transfer, intake and exhaust of the working fluid. The model has been validated with available experimental data in order to assess its accuracy and, at the same time, to calibrate the implemented sub-models. The influence of some geometrical parameters on the expander performances has been assessed. In particular, a study of the influence of the wrap geometry is presented. The results show that the circular cutter approach returns better performances at the expenses of a higher mass consumption. Nevertheless, the circular cutter modification returns a higher specific work. Lastly, the influence of one of the PMP parameters on performances has been assessed. The results show a fairly strong dependence of both mechanical power and specific work, suggesting that the global optimization of all geometric parameters of the scroll expander may radically improve its performances
Impact of Ozone Addition to Gasoline Surrogates Combustion in Spark Ignition Engine
No full textBased on the experimental results, a 3-D Computational Fluid Dynamics investigation is carried out to evaluate the influence of ozone on the combustion process in spark ignition engine fueled with gasoline/air mixtures. Ozone (O3) is a chemically reactive species capable of improving the laminar flame speed, reducing the ignition delay time, and stabilizing combustion variability. With the aim of proposing a 3-D numerical model to simulate combustion of fuel mixtures under ultra-lean conditions, two numerical correlations are proposed to reproduce the chemical properties of gasoline/air/ozone mixtures in terms of laminar flame speed. A chemical kinetic mechanism for Toluene Reference Fuel oxidation (iso-octane, n-heptane, toluene, 63/20/17% by mol.) modified with an ozone sub-mechanism is used to perform several 1-D numerical simulations. The laminar flame speed correlation estimates an enhancement of 3.4% at 600 K and 10 bar under ultra-lean condition (φ = 0.6). For the 3-D numerical simulations, the G-Equation model is used to reproduce the premixed combustion process in internal combustion engines. The results suggest that the numerical correlations can predict the combustion properties of gasoline/air mixtures without and with ozone addition. The presence of ozone traduces in a higher laminar flame speed, leading to an increase in the in-cylinder pressure peak and the rate of fuel consumption. Furthermore, the numerical analysis reveals that the greatest improvement is observed for fluid regions within the cylinder characterized by low turbulent flame speed
Small scale Organic Rankine Cycle testing for low grade heat recovery by using refrigerants as working fluids
No full textIn the last two decades, big efforts have been addressed to investigate new technologies for emissions abatement and oil dependence reduction. Among these, technologies focused on heat recovery from thermal processes or using low grade heat as energy source (i.e. geothermal, solar), have been gained big attention by the scientific community. In this paper, a small Organic Rankine Cycle (ORC) plant was tested under different operating conditions and by using refrigerants (R245fa) as working fluids. During these first operational tests the plant was operated only in regenerative layout (i.e. heat from hot fluid coming out of the expander, was partially recovered in the regenerator to preheat liquid fluid at the pumping outlet section). The performances of each of them (first law efficiency, exergy efficiency) were evaluated by imposing the expander inlet temperature and the electrical load at the generator. A simple mathematical model, was also used to predict the reference value of each of the parameter investigated. © 2018 AMSE Press. All rights reserved
Lattice Boltzmann Simulations of Particle Motion in a Turbulent Channel Flow
No full textParticle resolved direct numerical simulations (PR-DNS) of particle-laden turbulent flow in a channel are carried out to understand the effect of particle Stokes number (St) on their motion. The study focuses on particles which are larger than the Kolmogorov scale. The forces that impact this motion are factored into the discussion. The lattice Boltzmann method (LBM) is employed for the simulations. The scheme employed is able to resolve the surface of the particle and a method is adopted to account for the exchange of momentum between the particles and fluid as the particles move on fixed lattices. The simulations show that particles with relatively lower St move preferentially toward the wall while those with higher St exhibit a relatively uniform concentration
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