• Energy Research
• Restricted close
• other engineering and technologies close
• DE close
• EU close

Abstract Food transport and storage at low temperatures is a matter worldwide due to changes of the dietary habits and the increasing of the population. The issue of improving food storage applies at different applications such as commercial freezers or refrigerated trucks. The aim of this work is to improve the thermal performance of commercial freezers using phase change materials (PCMs) under door openings and electrical power failure. A commercial PCM was selected (Climsel-18) with a melting temperature of −18 °C, which is contained in 10 mm thick stainless steel panels placed at different locations in the freezer. During 3 h of electrical power failure, the use of PCM maintained the freezer temperature 4–6 °C lower and that of the frozen products remains at acceptable levels for much longer time. With frequent door openings the benefit of the PCM is evident when the temperature of the cabinet is near the melting temperature of the PCM.

A laminar drop tube reactor (DTR) was used to perform fast pyrolysis of walnut shells, a ligno-cellulosic biomass sample, in nitrogen and carbon dioxide atmospheres. The DTR reached the temperature of 1300 degrees C and the heating rate of 10(4)-10(5) degrees C/s. Char samples collected at different residence times along the reactor were characterized by ultimate and proximate analysis and by SEM. Char combustion reactivity was then measured by non-isothermal thermogravimetric analysis (TGA) in air. The analyses show that at residence times of 66 ms pyrolysis in N-2 is not complete, whereas it is complete in CO2. For residence times of 115 ms the differences between samples produced in N-2 and CO2 atmospheres level off.

The ITER large power supplies of the superconducting magnets and heating and current drive systems, fed by the Pulsed Power Electrical Network, can absorb from the grid active and reactive power up to 500 MW and 950 Mvar respectively. In this paper, a new analytical approach based on the state space formulation is proposed to investigate the dynamic stability of such complex system, including the main power components and their control, with the aim of identifying possible instability phenomena due to interactions among the ac/dc converters, reactive power compensation systems and related controllers. This model describes the dynamics of the main components of the ITER pulsed power supply systems and it is based on small signal approach to tackle the non linearity of the ac/dc conversion and reactive power compensation systems; the discrete phenomena have been approximated by continuous transfer functions, so the linear control theory can be applied for the stability analysis, making this method very effective and fast. Moreover a modular approach is adopted; thus this analytical model can be also easily adapted to other similar electrical power systems.

ABSTRACT Improving the comfort of public transport buildings is a mean to arouse the public interest in its use. The available studies concerning transport stations with semi-outdoor configurations barely emphasize local thermal discomfort. Generally, these studies produce a somewhat superficial approach to the subject, relying on the direct application of the standards (ISO 7730 and ASHRAE 55). Since the characteristics of most transport stations differ from the scope of the standards, the direct application of these standards does not represent the real thermal discomfort due to draught sensed by the users. The aim of this study is to propose a new approach able to predict the percentage of dissatisfied people due to draught in semi-outdoor spaces. An experimental campaign was conducted in a transport station with a semi-outdoor configuration, where 575 passengers were surveyed about the sensation of air movement, while air temperature and air velocity were measured. Through the collected data, it was possible to propose an alternative draught model (aDR) to assess the local thermal discomfort due to draught in semi-outdoor spaces.

A thermodynamic Aspen Plus simulation model for a reversible solid oxide fuel cell (RSOFC) is presented and evaluated. It is composed of an electrolysis and a fuel cell module. The latter is based on an existing non reversible SOFC model. The electrolysis model simulates water electrolysis as well as catalytic reactions of inlet gases. The model has been validated using data from literature. It has been found that the support layer on fuel electrode supported cells has to be treated differently in terms of diffusion than the active layer. Simulation results show that for the investigated cell parameters, the positive effect of adding CO2 to the steam feed on the electrolysis process is due to wateregas-shift reactions and not CO2 electrolysis. An analysis of outlet gas compositions in electrolysis mode showed that the assumption of the cell as an equilibrium reactor was justified. A parameter study has been conducted, showing that increasing the operation temperature and pressure can improve the overall performance, while changing the inlet gas compositions in general improves either fuel cell or electrolysis mode and deteriorates performance for the other mode.

A fuel cell is an exothermic device that wastes ca. 50% of the input chemical energy while methanol steam-reforming (MSR) reaction is endothermic. The integration of a low temperature methanol steam-reforming cell (MSR-C) with a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) in a combined stack arrangement allows the thermal integration of both reactors. A novel bipolar plate of poly(p-phenylene sulfide) (PPS) featuring the fuel cell flow field in one side and the reformer flow field in the other was designed, built and assessed. For the first time are reported high current densities (>0.5 A cm-2) with the integrated system running at 453 K. The system was also ran for more than 100 h at 453 K, at 0.3 A cm-2, with a methanol conversion of>90%. It was observed some degradation of the membrane electrode assembly (MEA) due to the continuous presence of methanol in the reformate stream. Electrochemical impedance spectroscopy (EIS) analyses revealed an overall increase of the resistances. The self-thermal sustainability of the combined device was only reached for >0.75 A cm-2 due to the poor thermal insulation of the combined reactor.

Abstract Open-air swimming pools in Mediterranean climate regions are heated by direct solar radiation with no auxiliary heating systems. In order to extend the swimming season or improve comfort conditions, solar collectors or pool coverings may be used. In this paper, another approach was followed through the use of phase change materials (PCM). Two methods of introducing the PCM were considered: (1) encapsulated in the sidewalls and bottom of the pool, and (2) use the PCM in an external heat exchanger. Heat is stored when water temperature is sufficiently high, while it is released when water temperature drops below comfort levels. A numerical model was built and validated for predicting the evolution of the water temperature, by taking into account meteorological data at three different locations in north-east of Spain. The simulations showed that using phase change materials provided some improvement of water conditions, especially when used in an external heat exchanger.