An innovative heat exchange device has been recently proposed, which employs an intermediate solid medium to transfer heat from a gas flow at low pressure and high temperature to another gas flow at higher pressure but lower temperature, with negligible pressure losses. In this paper, a key component of this innovative heat exchanger is analyzed in deep, namely the pressurization device responsible for the particles transit between the two separate environments. The operation of the proposed pressurization system is described in detail and then modeled as a zero-dimensional time-dependent system to analyze the influence of the related mass and energy losses onto the heat exchanger efficiency. An experimental test rig reproducing the pressurization tank has been also set up: the data collected at different operating conditions confirmed the reliability of the analytical model and the negligible energy losses occurring in the pressurization process.""" AMORUSO Vitantonio"

Nowadays, the development of new power plants capable of effectively using non-conventional energy sources is strongly desirable in order to obtain a significant reduction in costs of energy. In this regard, this paper proposes a new small scale (about 100 kW) combined cycle plant which can be fired externally by any kind of biomass. Particularly, the research activity presented here is concerned with the preliminary design of this innovative plant, which will be built, by means of a project funded by “Apulia Region”, at the LabZero Research Centre of Polytechnic University of Bari in the south of Italy. The goal of the paper is to demonstrate the effectiveness of the plant in terms of energy efficiency and availability and reliability of its components. The plant is mainly composed of a centrifugal compressor and a centripetal turbine of an automotive turbocharger, with the working fluid (clean air) being heated in a high temperature heat exchanger (HTHE) by using hot flue gases produced in an external combustion chamber burning biomass. The clean hot air expands in the turbine and then feeds the combustion chamber, where biomass is burned. In order to increase the efficiency, the flue gases exiting the HTHE are delivered into a heat recovery steam generator to generate water steam which can finally expand through a rotary actuator. Two configurations, employing an open Rankine cycle and a close one respectively, are analysed, and the use of biomass is compared with methane.

This paper evaluates the effects of cavitation upon the performance of a hydraulic, proportional, directly-operated, directional valve by means of thorough experimental and numerical investigations. The experimental campaign is performed to estimate how cavitation changes the performance curves of the valve; in particular, the experimental equipment assembled to control the cavitation phenomenon inside the proportional valve is described, and the influence of cavitation on the flow rate and the flow coefficient as a function of the spool position is assessed. In addition, a full three-dimensional mixture model of the flow field within the valve is developed to accurately predict cavitation within the flow path for several spool positions. The accuracy of the numerical model is proven by previous experiences and by comparing the numerical results with the experimental data. After their validation, the numerical predictions are employed to analyse the characteristics of cavitation that cannot be experimentally evaluated, such as the volume of vapour, and to identify the zones where cavitation occurs. The numerical simulations are finally employed to predict how the variation in cavitation intensity influences the driving forces required to move the sliding spool and to calculate the minimum cavitation number for which the effects of cavitation are negligible.

The aim of this paper is to propose an effective technique which employs a proportionalintegral Fuzzy logic controller for the thrust regulation of small scale turbojet engines, capable of ensuring high performance in terms of response speed, precision and stability. Fuzzy rules have been chosen by logical deduction and some specific parameters of the closed loop control have been optimized using a numerical simulator, so as to achieve rapidity and stability of response, as well as absence of overshoots. The proposed Fuzzy logic controller has been tested on the Pegasus MK3 microturbine: the high response speed and precision of the proposed thrust control, revealed by the simulations, have been confirmed by several experimental tests with step response. Its stability has been demonstrated by means of the frequency response analysis of the system. The proposed thrust control technique has general validity and can be applied to any small-scale turbojet engine, as well as to microturbines for electricity production, provided that thrust being substituted with the net mechanical power.

Purpose – The purpose of this paper is to present a full 3D Computational Fluid Dynamics (CFD) analysis of the flow field through hydraulic directional proportional valves, in order to accurately predict the flow forces acting on the spool and to overcome the limitations of two-dimensional (2D) and simplified three-dimensional (3D) models. Design/methodology/approach – A full 3D CAD representation is proposed as a general approach to reproduce the geometry of an existing valve in full detail; then, unstructured computational grids, which identify peculiar positions of the spool travel, are generated by means of the mesh generation tool Gambit. The computational grids are imported into the commercial CFD code Fluent, where the flow equations are solved assuming that the flow is steady and incompressible. To validate the proposed computational procedure, the predicted flow rates and flow forces are compared with the corresponding experimental data. Findings – The superposition between numerical and experimental curves demonstrates that the proposed full 3D numerical analysis is more effective than the simplified 3D flow model that was previously proposed by the same authors. Practical implications – The presented full 3D fluid dynamic analysis can be employed for the fluid-dynamic design optimization of the sliding spool and, more generally, of the internal profiles of the valve, with the objective of reducing the flow forces and thus the required control force. Originality/value – The paper proposes a new computational strategy that is capable of recognizing all 3D geometrical details of a hydraulic directional proportional valve and that provides a significant improvement with respect to 2D and partially 3D approaches.

This paper proposes the design of an innovative high temperature gas-to-gas heat exchanger based on solid particles as intermediate medium, with application inmediumand large scale externally fired combined power plants fed by alternative and dirty fuels, such as biomass and coal. An optimization procedure, performed by means of a genetic algorithm combined with computational fluid dynamics (CFD) analysis, is employed for the design of the heat exchanger: the goal is the minimization of its size for an assigned heat exchanger efficiency.Two cases, corresponding to efficiencies equal to 80% and 90%, are considered.Thescientific and technical difficulties for the realization of the heat exchanger are also faced up; in particular, this work focuses on the development both of a pressurization device, which is needed to move the solid particles within the heat exchanger, and of a pneumatic conveyor, which is required to deliver back the particles from the bottom to the top of the plant in order to realize a continuous operation mode. An analytical approach and a thorough experimental campaign are proposed to analyze the proposed systems and to evaluate the associated energy losses.

This article proposes an effective methodology for the fluid-dynamic design optimization of the sliding spool of a hydraulic proportional directional valve: the goal is the minimization of the flow force at a prescribed flow rate, so as to reduce the required opening force while keeping the operation features unchanged. A full three-dimensional model of the flow field within the valve is employed to accurately predict the flow force acting on the spool. A theoretical analysis, based on both the axial momentum equation and flow simulations, is conducted to define the design parameters, which need to be properly selected in order to reduce the flow force without significantly affecting the flow rate. A genetic algorithm, coupled with a computational fluid dynamics flow solver, is employed to minimize the flow force acting on the valve spool at the maximum opening. A comparison with a typical single-objective optimization algorithm is performed to evaluate performance and effectiveness of the employed genetic algorithm. The optimized spool develops a maximum flow force which is smaller than that produced by the commercially available valve, mainly due to some major modifications occurring in the discharge section. Reducing the flow force and thus the electromagnetic force exerted by the solenoid actuators allows the operational range of direct (single-stage) driven valves to be enlarged.