• Energy Research

The large use of portable devices imposes a new interest in the development of power backup systems with constraints in terms of compactness and safety. Such systems have to match the use as battery backups as well as a self-standing operating. Thermoelectric generators (TEGs) allow access to new ways of power supply thanks to their long lifetimes, their competitive efficiencies at low powers and their capability of providing multiple outputs. In this work, a TEG based on catalytic combustor has been proposed aiming to approach electrical output and dimension of the commonly used AA batteries. Catalytic combustion provides the possibility to profit from the high power densities of hydrocarbon in limited space and low burning temperatures meeting the needs of the TEGs as a heat engine. The system has been characterized for different fuel flow rates. The measured TEG efficiency is 3.4% with the electrical power output of 5.3 W. The system thermal behavior has been experimentally investigated according to literature models, by evaluating the effectiveness of the design and of the chosen practical solutions. The system produced reached the electrical output target, matching the characteristics proper of most of the common commercial AA batteries in a similar device volume.

Heating by gas combustion is widespread in residential and industrial environments, through the use of different types of systems and plants. A relevant case is that of gas stoves, where the heat-radiating unit operates autonomously with local gas feeding. A thermoelectric generator (TEG) can be integrated within this type of autonomous gas heater, for local production of electric power, so that devices requiring electric power can be added, where desired, without the need for any connection to the electrical grid. This approach can also lead to easier installation and operation, and eventually increases the overall efficiency. Following the development plan presented in a previous report, a new prototype of an autonomous gas heater for outdoor use has been implemented through the integration of an improved TEG device with a simple and robust design, which can be easily operated by the end-user. A small amount of heat is withdrawn and converted into electricity by the TEG, providing self-sustaining operation and, moreover, powering additional functions such as high-efficiency light-emitting diode lighting.

In recent years, the portable technology is receiving a great interest and significant improvement due to the progresses in electronic technology development and energy storage solutions. The decrease in power requirements for working energy systems, due to the increased efficiency and to the reduction in components size, opens the access to new solutions for power supplying. In particular, alternative backup systems for battery charging or replacement could be designed taking advantage of unconventional technologies. It is the case of small photovoltaic portable panels or fuel cells technology: in these solutions different sources are used to produce limited electrical powers required to keep devices on. In this paper, a thermoelectric solution for the power generation has been considered: the generator has been designed and assembled starting from a catalytic combustor. Catalytic combustion allows safe control of the processes, and the choice of a hydrocarbon fuel ensures the power availability and a fast recharge. The size of the system is set to fit a volume close to the one of AA batteries. The electrical power output obtained is close to 1 W with a cold side temperature below 40 °C. The limited values of these physical parameters allow obtaining a portable and safe device. The generator has been fully characterized in different ranges of fuel flow rates and the performances have been thoroughly analysed for processes optimization and efficiency improvement.

Abstract Mini channel solution is used in devices that require a high density of transmitted thermal power as a very large-scale integration design in computer systems and compact exchangers. Furthermore, the mini channels are extensively investigated in the literature for turbulent and laminar regimes. In this project, different configurations of mini channels have been studied to enhance heat transfer, using simulations with a commercial multi-physics code. Thanks to the results of the models, more promising configurations with 3D printing technique may be built. The project challenge is improving convective thermal power extracted by the exhaust gases of a mini-catalytic combustor. The combustor feeds six modules for thermoelectric power production (TEMs). As the first step, three different mini channel geometries have been chosen; the first one with 19 channels with rectangular cross-section, the second one with 6 channels with a convergent profile, and the latter with 2 channels with a fractal branching geometry. Simulations started from studying fluid dynamic to investigate the velocity field at the exit of the mini channels. The analysis has been extended by adding the conjugate heat exchange between fluid and combustor wall. The results show an increase in heat exchange compared to the base case for all configurations, with a maximum value for the 19 mini channels configuration.

The advances in miniaturized mechanical devices open exciting new opportunities for com- bustion, especially in the field of micro power generation, allowing the development of power-supply devices with high specific energy (small size, low weight, long duration). Even at 10% energy conversion efficiency hydrocarbon fuels can provide 10 times the energy den- sity of the most advanced batteries. Therefore, the growing interest in miniaturized devices is further boosted by the desire to replace batteries with hydrocarbon-based fuels for port- able power sources. In this context, both homogeneous combustion and catalytic reactors are of major interest. The development of a device based on catalytic combustor coupled with thermoelectric modules is particularly attracting for combustion stability and safety. Furthermore, when implemented in micro-meso scale devices, catalytic combustion allows fully utilization of the high energy densities of hydrocarbon fuels, but at notably lower operating temperatures than those typical of traditional combustion. These conditions are more suitable for coupling with conventional thermoelectric modules, preventing their degradation. In this work a novel catalytic meso-scale combustor fuelled with propane/air mixture has been coupled with two conventional thermoelectric modules. The wafer-like combustor is filled up with commercially-available catalytic pellets of alumina with Platinum (1% weight). In order to calibrate the operating conditions, the analysis of the temperature values and distribution across the combustor surfaces have been carried out. Characterization of exhaust gases concentration and of pellet aging were performed in order to investigate combustor properties. The results of the combustor behavior characterization guided the coupling of the combustor with commercially available thermoelectric modules using at the cold side a water cooled heat exchanger. The system obtained has been charac- terized in different operating conditions measuring the delivered electric power in different operating conditions. Efficiency estimation proves that the system is suitable for small port- able power generation.

The enhancement of energy performance of buildings has become a pillar of energy policies. The main target is the cut of energy consumption to reduce buildings footprint. This aim is pursued by introducing constrains on building requirements in terms of properties of basic materials and components and exploitation of renewable energy sources. That results in the definition of the zero-energy building (ZEB) concept. The new paradigm introduced new challenges and, at the same time, involved all the different stakeholders in facing the barriers to the diffusion of the novel solutions proposed by the research development. This paper summarizes the actual state-of-art of whole performance of ZEBs and the related technical solutions, analysing their increasing potential in energy consumption. A collection of the different case studies reported in literature involving ZEBs is presented, compiling an analysis of the performance of the common solutions actually applied. The technologies involved are described discussing their impact in meeting the ZEB requirements. A debate is proposed, pointing out the main aspects deserving further investigations and outlining the critical elements in making the zero-energy target the new standard for the buildings.

Heating by gas combustion is widespread in residential and industrial environments, through the use of different types of systems and plants. A relevant case is that of gas stoves, where the heat-radiating unit operates autonomously with local gas feeding and, eventually, electricity for an optional fan convector. A thermoelectric generator (TEG) can be integrated within this type of autonomous gas heater, for the local production of electric power, able to support electrical auxiliaries, where desired, without the need for any connection to the electrical grid. This approach can lead to easier installation and operation and, eventually, it increases the overall efficiency. Following the development work plan drawn in previous reports [1][2], a new prototype of an autonomous gas heater has been implemented through the integration of a TEG device with a simple and robust design, easily operated by the end user. A small amount of heat is withdrawn and converted into electricity by the TEG, providing self-sustaining operation and, moreover, powering new ancillary functions (e.g. fan convector) without extra electrical requirements and no need for an electrical connection.