Direct Drive Friction Welding: A Comprehensive Mathematical Model

This paper presents a theoretical study on direct drive rotary friction welding process and investigates the possibility of producing an analytical solution of the heat transfer equation, both during the first part of heating process and the second part of the process when the operative temperature of the material at the end of the rod is assumed to be constant and equal to plasticization temperature

High altitude airship cabin sizing, pressurization and air conditioning

This paper aims at defining a design methodology for the global thermodynamic performance of a high altitude airship cabin. This design method applies to different systems, which could not use the traditional air conditioning plant layout based on bleed air intake from the compressor stage of jet engines. In the case of electrically propelled green vehicles and airships, other energy sources must be exploited. The MAAT EU FP7 project presents an innovative, energetically self sufficient, airship system based on cruiser-feeder architecture. Both the cruiser and feeder are fed by photovoltaic energy. The energy storage system by electrolysis and fuel cells with intermediate energy storage by hydrogen and oxygen is characterized by high temperature energy dispersions (about 800-1000°C for High temperature SOFC cells). This situation encourages the definition of a novel pressurization and air conditioning system. A preliminary cabin sizing with some structural considerations, an energetic evaluation of the thermal insulation of the cabin and a general balance of the energy production system are provided

PHOTOVOLTAIC PRODUCTION OF HYDROGEN AT STRATOSPHERIC ALTITUDES

This paper compares hydrogen production by photovoltaic powered electrolysis of water at sea level and at low stratospheric altitudes up to 21 km. All the hydrogen production process has been considered from catchable solar radiation to storage technologies. The evaluation has been performed for 1 m2 of flat horizontal plane. It has been considered the electric energy amount produced by considering the equilibrium temperature of PV modules and its evolution due to external temperature and solar radiation. Hydrogen production through electrolysis has been evaluated too. Two different methods of hydrogen storage have been evaluated: high pressure compression up to 20 MPa and liquefaction process. The energetic cost of both production processes has been evaluated. The comparison is presented in terms of effective energy deliverable to final users considered in terms of HHV. This evaluation considers also, in the case of liquefaction process the energy which can be recovered by the regasification process

Design methods of Coanda effect nozzle with two streams

This paper continues recent research of the authors about the ACHEON Coanda effect two streams nozzle. This nozzle aims to produce an effective deflection of a propulsive jet with a correspondent deviation of the thrust vector in a 2D plane. On the basis of a previously published mathematical model, based on integral equations, it tries to produce an effective design guideline, which can be adopted for design activities of the nozzle for aeronautic propulsion. The presented model allows defining a governing method for this innovative two stream synthetic jet nozzle. The uncertainness level of the model are discussed and novel aircraft architectures based on it are presented. A CFD validation campaign is produced focusing on validating the model and the designs produced

Simulazioni numeriche di fenomeni termofluidodinamici

In un precedente lavoro, e` stato affrontato, mediante l'utilizzo di codici numerici, il problema della definizione del campo di moto e di temperatura indotto da una lama d'aria; analizzando lo stesso problema, viene ora effettuato il confronto fra la soluzione numerica di una procedura, che per tempi, costi e livello di approfondimento dei suoi fondamenti teorici e` ottenibile da un progettista, ed una pi\uf9 accurata, che necessita pero` di risorse di calcolo oggi non facilmente accessibili

Theoretical and experimental analysis of two passive cooling systems for the solar cells without concentration

L'articolo analizza diversi sistemi di rafreddamento di sistemi fotovoltaici, confrontandone pregi e benefici

A Probabilistic Forecast-Driven Strategy for a Risk-Aware Participation in the Capacity Firming Market: extended version

This paper addresses the energy management of a grid-connected renewable generation plant coupled with a battery energy storage device in the capacity firming market, designed to promote renewable power generation facilities in small non-interconnected grids. The core contribution is to propose a probabilistic forecast-driven strategy, modeled as a min-max-min robust optimization problem with recourse. It is solved using a Benders-dual cutting plane algorithm and a column and constraints generation algorithm in a tractable manner. A dynamic risk-averse parameters selection strategy based on the quantile forecasts distribution is proposed to improve the results. A secondary contribution is to use a recently developed deep learning model known as normalizing flows to generate quantile forecasts of renewable generation for the robust optimization problem. This technique provides a general mechanism for defining expressive probability distributions, only requiring the specification of a base distribution and a series of bijective transformations. Overall, the robust approach improves the results over a deterministic approach with nominal point forecasts by finding a trade-off between conservative and risk-seeking policies. The case study uses the photovoltaic generation monitored on-site at the University of Li\`ege (ULi\`ege), Belgium.Comment: Extended version of the paper accepted for publication in IEEE Transactions on Sustainable Energ

Laminar Flow Heat Transfer with Axial Conduction in a Circular Tube: a Finite Difference Solution

A finite difference technique is developed for evaluating the rate of heat transfer in the thermal entrance region of ducts with axial conduction. The pipe is assumed to extend from minus to plus infinity, while the velocity profile is fully developed. The boundary condition selected is a uniform heat flux for z greater than or equal to 0, while the wall temperature is kept uniform and equal to its minus infinity value for z less than 0. The results show that axial conduction and heat losses from the unheated section of the pipe significantly affect the temperature profile at the inlet of the heated part lower than the local mixed mean temperatures immediately downstream from the start of the heating. It is found that the performance of this type of heat exchanger can be described by a new parameter as an alternative to the usual Nusselt number