Results 21 - 30 of 199915
Results 21 - 30 of 199915. Search took: 0.065 seconds
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[en] Highlights: • We developed a thermoelectric cap (TC) to harvest hydrothermal energy. • The TC was deployed at a hydrothermal vent site near Kueishantao islet, Taiwan. • The TC monitored the temperature of the hydrothermal fluids during the field test. • The TC could make the thermal energy of hydrothermal fluids a viable power source. - Abstract: Long-term in situ monitoring is crucial to seafloor scientific investigations. One of the challenges of operating sensors in seabed is the lifespan of the sensors. Such sensors are commonly powered by batteries when other alternatives, such as tidal or solar energy, are unavailable. However, the batteries have a limited lifespan and must be recharged or replaced periodically, which is costly and impractical. A thermoelectric cap, which harvests the thermal energy of hydrothermal fluids through a conduction pipe and converts the heat to electrical energy by using thermoelectric generators, was developed to avoid these inconveniences. The thermoelectric cap was combined with a power and temperature measurement system that enables the thermoelectric cap to power a light-emitting diode lamp, an electronic load (60 Ω), and 16 thermocouples continuously. The thermoelectric cap was field tested at a shallow hydrothermal vent site near Kueishantao islet, which is located offshore of northeastern Taiwan. By using the thermal gradient between hydrothermal fluids and seawater, the thermoelectric cap obtained a sustained power of 0.2–0.5 W during the field test. The thermoelectric cap successfully powered the 16 thermocouples and recorded the temperature of the hydrothermal fluids during the entire field test. Our results show that the thermal energy of hydrothermal fluids can be an alternative renewable power source for oceanographic research.
[en] The concepts of the cities we know nowadays, and which we are accustomed to, change at a very rapid pace. The philosophy of their design is also changing. It will base on new standards, entering a completely different, futuristic dimension. This stage is related to changes in the perception of space, location and lack of belonging to definite, national or cultural structures. Cities of the future are cities primarily intelligent, zero-energetic, zero-waste, environmentally sustainable, self-sufficient in terms of both organic food production and symbiosis between the environment and industry. New cities will be able to have new organisational structures—either city states, or, apolitical, jigsaw-like structures that can change their position—like in the case of the city of Artisanopolis, designed as a floating city, close to the land, reminiscent of the legendary Atlantis. This paper is focused on the main issues connected with problems of the contemporary city planning. The purpose of the research was to identify existing technological solutions, whose aim is to use solar energy and urban greenery. The studies were based on literature related to future city development issues and futuristic projects of the architects and city planners. In the paper, the following issues have been verified: futuristic cities and districts, and original bionic buildings, both residential and industrial. The results of the analysis have been presented in a tabular form.
[en] Here we present the different aspects of the EUROSUNMED project. The scientific targets of EUROSUNMED are the development of new technologies in three energy field areas, namely photovoltaics (PV), concentrated solar power (CSP) and grid integration (GI), in strong collaboration with research institutes, universities and SMSs from Europe in the north side of the Mediterranean sea and from Morocco and Egypt from the south of the sea. the focus in PV will be on thin film (Si, CZTS) based solar cells and modules while the goal in CSP field is to design and test new heliostats as well as novel solutions for energy storage compatible with these technologies. The project aims at producing components that will be tested under specific conditions of MPC (hot climate, absence of water, etc.). Such investigations are complemented with studies on grid integration of energy sources from PV and CSP in Morocco and Egypt context. Additionally, the consortium envisages training PhD students and post-docs in these interdisciplinary fields (chemistry, physics, materials science) in a close and fruitful collaboration between academic institutions and industry from EU and MPCs. The consortium is well placed around leading academic groups in materials science and engineering devices and equipments for the development of PV and CSP, and also in the promotion of the renewable energies in general. Moreover, technology transfer and research infrastructure development in the targeted areas will be provided. Disseminating the results of the projects will be done through the organization of summer schools and stakeholders involved in the 3 selected energy area and beyond. Another outreach of the project will be the proposal for a roadmap on the technological aspects (research, industry, implementation) of the PV, CSP and grid area as well as on the best practice for the continuation of strong collaboration between the EU and MPCS partners and beyond for mutual interest. (author)
[en] Highlights: • The performance of an ejector in an Organic Rankine Cycle and ejector refrigeration cycle (EORC) was evaluated. • The achieved entrainment ratio and COP of an EORC system is affected significantly by the evaporator conditions (such as temperature, pressure and flow rate). • An optimum distance of 6 mm nozzle position was found that ensures a maximum entrainment ratio, the best efficiency and lowest loss in the ejector. • A reduced total pressure loss between the nozzle inlet and exit leads to a lower energy loss, a higher entrainment ratio and better overall ejector performance. - Abstract: Power-generation systems based on organic Rankine cycles (ORCs) are well suited and increasingly employed in the conversion of thermal energy from low temperature heat sources to power. These systems can be driven by waste heat, for example from various industrial processes, as well as solar or geothermal energy. A useful extension of such systems involves a combined ORC and ejector-refrigeration cycle (EORC) that is capable, at low cost and complexity, of producing useful power while having a simultaneous capacity for cooling that is highly desirable in many applications. A significant thermodynamic loss in such a combined energy system takes place in the ejector due to unavoidable losses caused by irreversible mixing in this component. This paper focuses on the flow and transport processes in an ejector, in order to understand and quantify the underlying reasons for these losses, as well as their sensitivity to important design parameters and operational variables. Specifically, the study considers, beyond variations to the geometric design of the ejector, also the role of changing the external conditions across this component and how these affect its performance; this is not only important in helping develop ejector designs in the first instance, but also in evaluating how the performance may shift (in fact, deteriorate) quantitatively when the device (and wider energy system within which it functions) are operated at part load, away from their design/operating points. An appreciation of the loss mechanisms and how these vary can be harnessed to propose new and improved designs leading to more efficient EROC systems, which would greatly enhance this technology’s economic and environmental potential. It is found that some operating conditions, such as a high pressure of the secondary and discharge fluid, lead to higher energy losses inside the ejector and limit the performance of the entire system. Based on the ejector model, an optimal design featuring a smoothed nozzle edge and an improved nozzle position is found to achieve an improved entrainment ratio, significantly better performance and reduced energy losses in the ejector.
[en] Hourly DNI data from the Australian Bureau of Meteorology over 8 years have enabled analysis of implications for solar thermal power generation systems. Six sites were selected, mostly in central Australia and the occurrence and duration of gaps in the availability of energy inputs to solar thermal generation were tallied. In a three month period late in 2010 12 periods of three or more days with an overall average DNI of 2.3 kWh/m2/day occurred. The relationship between DNI and solar thermal generation efficiency was examined and this indicated that on many more days power output would have been very low or zero. The relation between daily total DNI and hourly average DNI was also found to be important, as a high total might be made up of many hours in which DNI was too low for significant generation. These two factors show that there is a significant problem of intermittency for solar thermal systems. Although the annual output of each plant may be commercially viable a solar thermal system might not be capable of meeting demand reliably. - Highlights: • Australian Bureau of Meteorology data were examined regarding DNI patterns. • Gaps in availability of solar energy were identified. • The occurrence of low hourly DNI was examined. • Implications for the reliability of solar energy were drawn
[en] Highlights: • Thermal enhancement in a thermoelectric liquid generator is tested. • Thermal enhancement is brought upon by flow impeding inserts. • CFD simulations attribute thermal enhancement to velocity field alterations. • Thermoelectric power enhancement is measured and discussed. • Power enhancement relative to adverse pressure drop is investigated. - Abstract: Thermoelectric power production has many potential applications that range from microelectronics heat management to large scale industrial waste-heat recovery. A low thermoelectric conversion efficiency of the current state of the art prevents wide spread use of thermoelectric modules. The difficulties lie in material conversion efficiency, module design, and thermal system management. The present study investigates thermoelectric power improvement due to heat transfer enhancement at the channel walls of a liquid-to-liquid thermoelectric generator brought upon by flow turbulating inserts. Care is taken to measure the adverse pressure drop due to the presence of flow impeding obstacles in order to measure the net thermoelectric power enhancement relative to an absence of inserts. The results illustrate the power enhancement performance of three different geometric forms fitted into the channels of a thermoelectric generator. Spiral inserts are shown to offer a minimal improvement in thermoelectric power production whereas inserts with protruding panels are shown to be the most effective. Measurements of the thermal enhancement factor which represents the ratio of heat flux into heat flux out of a channel and numerical simulations of the internal flow velocity field attribute the thermal enhancement resulting in the thermoelectric power improvement to thermal and velocity field synergy
[en] The potential and limits of solar thermal power systems depend primarily on their capacity to meet electricity demand in mid-winter, and the associated cost, storage and other implications. Evidence on output and costs is analysed. Most attention is given to central receivers. Problems of low radiation levels, embodied energy costs, variability and storage are discussed and are found to set significant difficulties for large scale solar thermal supply in less than ideal latitudes and seasons. It is concluded that for solar thermal systems to meet a large fraction of anticipated global electricity demand in winter would involve prohibitive capital costs. - Highlights: • Output and capital cost data for various solar thermal technologies is examined. • Special attention is given to performance in winter. • Attention is also given to the effect of solar intermittency. • Implications for storage are considered. • It is concluded that there are significant limits to solar thermal power
[en] Highlights: • The interaction between multiple boreholes is presented as an arising issue. • Thermal interaction among boreholes in long-term system operation is examined. • Effect of thermal interaction on heat pump COP is examined. • Borehole stores/removes heat in the ground under a periodic ground heat profile. • The analytical model is validated with a numerical finite volume approach. - Abstract: A semi-analytical model that couples a model outside the borehole with one inside the borehole is proposed. To examine the effect of temperature rise in the soil surrounding a vertical ground heat exchanger on the performance of an associated ground heat pump, the heat pump model should be coupled to the model inside the borehole and the conduction heat transfer model outside the borehole. The running fluid temperature, the borehole wall temperature and the heat load profile are the main coupling parameters between the three models. The results of the analytical model are compared with ones of a finite volume numerical model
[en] I-V and P-V characteristics of partially shaded solar modules have experimentally been investigated and modeled based on the Bishop model. It is shown that the decrease in the power production of such solar modules is not proportional to the area of the shaded surface