Experimental measurement technique for the assessment of the fuel crossover diffusion coefficient in the membrane electrode assembly of a direct methanol fuel cell

Since the cross-over still seems to be the main issue of the direct methanol fuel cells, an experimental evaluation of the diffusive cross-over is performed. Even if the relationship of the rate through the membrane is the sum of the three terms of diffusive, osmotic and drag, the diffusive component is also present at open circuit lowering the Open Circuit Voltage of the single cell up to 50 % with respect to the Nernst potential. The goal of the research is to develop a direct measurement technique of the crossover that can provide the effective values of the parameters that characterize the membrane electrode assembly. The experimental set up consists in the pressure, flow and temperature control and acquisition using Labview. A sensitive analysis for three values of temperatures at 60°C, 65°C and 70°C is performed for first. Then, a small overpressure was generated in the cathode side by a valve located at the cathode outlet. A set of pressure were analysed for 0, 30 and 90 mbar of overpressure at the cathode. The tested fuel cell has a commercial Nafion 117 membrane and carbon paper gas diffusion layers 700 cm2 large. Preliminary results show that the differential concentration term seems to be significantly larger than the osmotic term. The diffusion coefficients are useful for fuel cell modelling and for the calibration of the operating conditions in the sensor less DMFC systems

Evaluation methodology for energy efficiency measures in industry and service sector

Directive 2012/27/EU, transposed in Italy with Decree of 4 July 2014 No102, a common framework of measures for the promotion of energy efficiency in European Union, is an innovative tool for improvement of energy efficiency and also necessary to undertake main objective of European Union (save 20% of primary energy consumption by 2020). Large enterprises and energy-intensive firms, except those having an energy management system (EnMS) according to ISO 50001 or compliant with EMAS Eco-Management and Audit Scheme or ISO 14001 fall under obligations and must be carry out energy audits every 4 years starting by December 2015 having "SMART" requirements: be Specific, Measurable, Accessible, Realistic, Time related. The analysis on a sample of Italian companies, mainly of small and medium enterprises (SME) in industry and the service sector, was conducted. Energy audit was carried out to identify Energy Company Profile, rationalize energy consumption to increase energy efficiency, assessing potential for energy savings and reducing of environmental impact. For any business context a series of energy efficiency measures has been proposed, selecting high profitability energy saving options by applying a priority criterion. Technical and economic indicators were reported on best practices focusing on tertiary sector and also industry. The study, starting from the feasibility assessments, aims to establish a possible correlation between energy performance indicators (EnPIs) and a limited number of parameters of the energy systems, in terms of production, operation and power consumption. Comparative assessment of energy-saving measures provides an useful method for assessing applicability of standard energy-saving measures in similar contexts and cost-effectiveness of solutions, as a function of a limited number of parameters

Assessment of CO2 bubble generation influence on direct methanol fuel cell performance

Fuel cells fed directly by liquid methanol represent a class of suitable devices for supply portable small power applications. To become a market attractive technology some issues must be properly addressed and resolved. The presence of gaseous CO2 generated in the anode channels is the main issue as it can hinder the free surface of the Gas Diffusion Layer reducing the active area and the methanol flux through the porous media towards the catalyst layer. In this work the influence of gas phase fraction on the cell performance and the relationship with the operating parameters such as air flow rate, methanol-water solution flow rate and current density is investigated. The characterization of CO2 bubbles flow in the anode channel is carried out

Energy and thermodynamical study of a small innovative compressed air energy storage system (micro-CAES)

There is a growing interest in the electrical energy storage system, due to the high penetration of the energy produced by renewable sources, the possibility of leveling the absorption peak of the electric network (peak shaving) and the advantage of separating the production phase from the exertion phase (time shift). Compressed air energy storage systems (CAES) are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, a result of the mathematical model created in a Matlab/Simulink® environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. This is something promising for the development of an experimental devic

Influence of the façades convective heat transfer coefficients on the thermal energy demand for an urban street canyon building

In an urban micro-climate environment, the convective heat transfer coefficient (CHTC) on the façades influences simulated building's energy demand and exterior wall surfaces temperatures. In this paper, it is analyzed how the CHTC values on the façades of a building located in an urban canyon influence the façades temperatures and how important is the choice of an accurate CHTC correlation on the space cooling and heating energy demand. CHTC correlations found in literature are based on some specific micro-climate parameters such as local wind speed, district construction density, temperature differences between façades and canyon air and wind direction. An accurate choice of the right correlation for the simulated urban environment is important to better represent the exterior walls heat removal due to outside wind climate. The effects of the use of different CHTC correlations have been evaluated by means of TRNSYS 17.0 simulation program. The study is performed for a building sited an urban street canyon with the aspect ratio H/W=1 and located in a Mediterranean climate, in Rome. The comparison performed between the results of the numerical simulations shows that some correlations lead to an underestimation of the space heating demand around 9.7% and to an overestimation of the space cooling demand around 17.5%

Impact of carrier dynamics on the photovoltaic performance of quantum dot solar cells

The study presents a theoretical investigation of the impact of individual electron and hole dynamics on the photovoltaic characteristics of InAs/GaAs quantum dot solar cells. The analysis is carried out by exploiting a model which includes a detailed description of quantum dots (QD) kinetics within a drift-diffusion formalism. Steady-state and transient simulations show that hole thermal spreading across the closely spaced QD valence band states allows to extract the maximum achievable photocurrent from the QDs; on the other hand, slow hole dynamics turns QDs into efficient traps, impairing the short circuit current despite the extended light harvesting provided by the QDs

Applications of Micro-CAES Systems: Energy and Economic Analysis☆

Abstract The present study concerns the development of a micro-CAES system for thermal and electrical energy storage for residential and non-residential users (shelter/remote users including), in order to reduce energy costs and increase the reliability of energy supply from renewable sources. The micro-CAES system allows you to store the electricity generated from renewable and conventional sources to pressure energy. Further thermal energy can be recovered from conversion process, stored and used for space heating or hot water. The micro-CAES allows you to reduce peak energy demand by utilities (peak shaving), decrease the size of the power generation devices (downsizing), reduce the power of the contract with the grid operator, size the system on the load curve power users in order to increase energy efficiency and economic sustainability reducing management costs with the advantage to reduce operating costs, use of non-toxic materials, zeroing of GHG emissions (zero emission). The innovative technology is based on high-efficiency energy storage process via storage of compressed air at high pressure, quasi-isothermal compression of a mixture air-liquid for heat storage and supply of electrical power constant during the expansion. The air-liquid mixture with excellent ratio between the phases allows you to obtain quasi-isothermal compression, with maximum compression efficiency and high thermal exchange, it enables to have a constant electrical power during the expansion, at a constant pressure during discharge. A dedicated software enables to manage the micro-CAES system to adapt its operation as a function of external conditions and user requirements. An energetic and economic analysis has been performed identifying the optimal size reference. The power supply system provides for the integration of small wind and photovoltaic with a storage system based on micro-CAES. The technological challenge is to be able to ensure a constant power level selected throughout the day

Mobile Platform of SRF Production and Electricity and Heat Generation

Abstract The technological frontier is ripe for action on the cycle of municipal waste at local level through the optimization of existing treatment processes, adapting to European Union directives. The study concerns the analysis of the waste cycle in order to rationalize the current paths of the waste by adapting to EU directives, with a view of the entire supply chain - from the delivery to the energy production (WtE, Waste to Energy) – with a intermediate stage of SRF (Solid Recovered Fuel) production. The DIMA has developed an innovative platform for MSW treatment (unsorted and not), based on newly developed technologies that enables its weight and volume reduction and the transformation in SRF high quality, by achieving consistent chemical-physical and particle size parameters through the innovative technology of mechanochemical micronization. This standardized fuel product is therefore suitable for energy recovery within the platform using the most advanced gasification process. The study aims at developing a mobile demonstration plant of 100-200 kWe for energy recovery from waste in cogeneration by conversion of MSW into SRF through a system of characterization, treatment and recycling based on a highly innovative mechanochemical refining system. The SRF is enhanced through more advanced gasification process and it can used for the production of electricity and thermal energy. The production, the gasification and the syngas combustion take place in modular units arranged in appropriate mobile units (containers) appropriately configured, to fully meet the objectives of a sustainable policy management and security of waste. b Unit 1 (waste treater - SRF producer) is developed to operate the transformation of industrial waste in SRF for subsequent gasification inside unit 2 (Boiler Gasifier). It carries out a pre-treatment and mechanochemical micronization waste treatment. The SRF is reduced into pellets to be introduced into the 2 (boiler gasifier) to its gasification (syngas production). The pellet (auxiliary unit 4, pellettizer) is gasified in the unit 2 and enriched in order to obtain synmethan gas for producing electricity in the cogeneration unit 3 (energies production)