• Energy Research

Abstract The legislation of various European countries imposes limits on the demand for building heating and cooling in order to reduce the primary energy consumptions. Moreover, the legislation prescribes that a fraction of the demand for building cooling, heating and power must be met through renewable energy sources. Among renewable energy systems, wind power, solar photovoltaic, solar thermal energy, solar cooling and heat pumps (though only “partially” renewable) have to be mentioned. In this framework combined heat and power (CHP) systems can provide a further solution to reduce the primary energy consumption. Due to the availability of different technologies, a key factor is the choice of the allocation strategy which allows the division of the energy demands among the various technologies in order to minimize the primary energy consumption. Since the cost of the technologies and the actual tariff and incentive scenarios depend on the specific country and may lead to not optimal allocation strategies in terms of primary energy consumption, these economic parameters are not taken into consideration in the analysis. Therefore, the obtained solutions represent a target which the policies should aim to achieve. This paper aims to develop and apply a methodology for the optimal allocation of the demand among CHP and renewable energy systems, with the aim of minimizing the primary energy consumption, by accounting for legislative constraints. The methodology is then applied to different climatic scenarios to evaluate the effects of a variation of the demand and technology characteristics on the allocation of the loads. Moreover, an analysis on the combined effects is presented. Finally, some guidelines are obtained.

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the micro-particles not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which areas of the compressor airfoils are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. The results show that micro-particles tend to follow the flow by impacting at full span with an higher impact concentration on the pressure side. The suction side is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid-dynamic phenomena such as separation, stagnation point and tip leakage vortex strongly influence the impact location of the particles.

Abstract Pumps are among the most spread machines in industrial facilities. In this work a comparative CFD analysis using different software is presented. The three-dimensional flow in the semi-open impeller and volute of a centrifugal pump is numerically simulated. The main advantage of semi-open impeller centrifugal pump is its efficiency which can be considered constant thanks to the clearance adjustment. In addition this kind of impeller is less likely to clog with solid bodies (important in case of slurry-processing). The open impeller has all the parts visible, so it is easier to inspect for wear and damages. Eventually it is lighter than a shrouded impeller: it can spin faster. The stress due to centrifugal force is indeed a limit for the speed of this machines. On the other hand its main disadvantage if compared to a shrouded pump is its lower efficiency due to the heavier tip leakage. In addition it cannot be employed in case of explosive products: the risk of contact between impeller and volute causing sparks is not negligible. The simulations have been carried out using both open-source and proprietary software: OpenFOAM®, PumpLinx ® and ANSYS-CFX ®. The performance of the machine handling both Newtonian and non-Newtonian fluids are also investigated. The numerical models and the results of the different computational strategies were compared with the experimental data and the accuracy of different software is evaluated in the case of Newtonian model. It is well known that the performance of a centrifugal pump drops processing a viscous fluid. Even so the behavior during the pumping of non-Newtonian fluids has not been investigated so far. The non-Newtonian fluid processed is a shear-thinning fluid (the apparent viscosity decreases with an increase stress). The slurries which are usually processed in the food industries, chemical plants and oil&gas processes show a usual behavior which correspond to this kind of model.

Abstract Centrifugal pumps are used in many applications in which non-Newtonian fluids are involved: food processing industry, pharmaceutical and oil/gas applications. In addition to pressure and temperature, the viscosity of a non-Newtonian fluid depends on the shear rate and usually is several orders of magnitude higher than water. High values of viscosity cause a derating of pump performance with respect to water. Nowadays, pumping and mixing non-Newtonian fluids is a matter of increasing interest, but there is still lack of a detailed analysis of the fluid-dynamic phenomena occurring within these machines. A specific design process should take into account these effects in order to define the proper pump geometry, able to operate with non-Newtonian fluids with specific characteristics. Only few approaches are available for correcting the pump performance based on the Hydraulic Institute method. In this work, an experimental and numerical campaign is presented for a semi–open impeller centrifugal pump elaborating non-Newtonian fluids. An on-purpose test bench was built and used to investigate the influence on pump performance of three different non-Newtonian fluids. Each pump performance test was accompanied by the rheological characterization of the fluid, in order to detect modifications of the rheological phenomena and allow a proper Computation Fluid Dynamics (CFD) modeling. The performance of the machine handling both Newtonian and non-Newtonian fluids are highlighted in relation with the internal flow field.

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the microparticles that are not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0 μm–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which areas of the compressor airfoils are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. The results show that microparticles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side (PS). The suction side (SS) is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, stagnation point, and tip leakage vortex, strongly influence the impact location of the particles.

Abstract In this paper, a full experimental characterization of a micro-scale ORC system is presented. The facility under investigation is driven by a piston expander prototype, made of three cylinders arranged radially around the drive shaft. The system is rated for a thermal input around 30 kW, being suitable for residential, tertiary sector or small industry applications. It is conceived for exploiting low temperature heat sources, such as solar collectors, biomass boilers, geothermal energy or waste heat streams. The facility was provided with an electric boiler as heat source, which warms water up to 90 °C, and cold water at ambient temperature as heat sink. A test campaign was performed varying the hot source temperature and the organic fluid feed pump velocity, in order to characterize the system behavior at different off-design working conditions. The electric consumption of the ORC feed pump was measured, in order to quantify the actual impact of the auxiliaries on the overall efficiency. Moreover, the number of electric loads connected to the generator was varied, changing the equivalent phase impedance value, for evaluating the effect on the expander rotating speed and power output. The experimental analysis demonstrated that small reciprocating expander is suitable for exploiting low enthalpy heat sources, with quite good performances compared to other architectures like scroll and screw expanders, more applied within low temperature sources. The results show that the gross electric power output varied between 250 W and 1150 W, depending on the expander speed and on the number of electric loads activated. The expander total efficiency showed a barely constant trend around 40%. The pump total efficiency varied between 10% and 20%, increasing with the pump rotational speed. The maximum ORC gross and net efficiency were 4.5% and 2.2% respectively, confirming that the auxiliaries impact cannot be considered negligible in such type of systems.

This paper investigates effects of interstage water injection on the performance of a GE Frame 7EA gas turbine using aero-thermodynamic modeling. To accomplish this objective a computational code, written in Fortran 90 language and developed by DIEM – University of Bologna, has been used. The calculation procedure considers effects of evaporation of injected water within the compressor including droplets dynamics which are necessary in order to fully evaluate effects of wet compression on the gas turbine performance. The robustness of the computational code is demonstrated by evaluating stage-by-stage compressor performance and the overall gas turbine performance in presence of inlet evaporative fogging, overspray fogging and interstage water injection. The presented results show that water injection location influences compressor stage loading redistribution differently. The plausible explanations to the observed trends of various performance parameters are presented in the paper.

In order to prevent machine malfunctions and to determine the machine operating state, it is necessary to use correct measurements from actual system inputs and outputs. This requires the use of techniques for the detection and isolation of sensor faults. In this paper an approach based on analytical redundancy which uses dynamic observers is suggested to solve the sensor fault detection and isolation problem for a single-shaft industrial gas turbine. The proposed technique requires the generation of classical residual functions obtained with different observer configurations. The diagnosis is performed by checking fluctuations of these residuals caused by faults.