Results 1 - 7 of 7
Results 1 - 7 of 7. Search took: 0.025 seconds
|Sort by: date | relevance|
[en] A thermodynamic engine cycle can be implemented by exploiting the temperature difference existing between the warm surface seawater and cold deep seawater. It employs a working fluid that evaporates by warm seawater, produces work in an expander device, such as a gas turbine and finally condenses by cold deep seawater. A new Carnot-based cycle for OTEC applications, called CAPILI cycle is presented. In this new engine cycle, work is produced by the movement of an inert liquid through a hydraulic turbine. This inert liquid characterized by a very low saturation pressure and immiscibility with the working fluid, acts as a liquid piston that moves alternately between two insulated cylinders. The insulated cylinders are connected alternately to an evaporator and a condenser, each of them operates at different pressure and temperature levels. A performance study which consists in a steady state energy balance is realised first to select the most suitable working fluid for this specific application. It was found that the best fluid is the HFC refrigerant R134a. A dynamic modelling based on the concept of equivalent Gibbs system is carried out to appreciate the dynamic behaviour and the performances of this new thermal conversion process. -- Highlights: ► A novel Carnot-based cycle operating with a liquid piston is investigated for OTEC application. ► The most suitable working fluid giving the best performances is found to be the HFC R134a. ► The performances of this new thermal process are evaluated using a dynamic modelling. ► A thermal efficiency of 1.9% can be obtained by exploiting seawater temperature difference of 20 °C. ► A net cycle efficiency of 1.2% is achieved considering a net to gross power production ratio of 61%.
[en] Considering the geographical position of South Korea, the concept of C-OTEC (Combined Ocean Thermal Energy Conversion) is thought to be feasible. C-OTEC uses the latent heat of the steam exhausted into the condenser of a power plant as a heat source, in contrast to the conventional OTEC cycle, which is based on warm surface water. More specifically, the C-OTEC heat source can always be maintained at around 32 °C which is the temperature of saturated steam when it is condensed. This paper describes the selection of the working fluid, thermodynamic analysis, and the impact on the Rankine cycle when providing steam to the C-OTEC process. Based on the analysis, C-OTEC is expected to be beneficial for power plants through increased output and plant efficiency. Especially in the case of old power plants which cannot easily maintain their rated output during the summer, C-OTEC is expected to help to improve the condenser vacuum, reduce the necessary pumping power, and reduce the temperature of the discharge side. Given the current economic scenario situation, the focus is on optimizing the fabrication of the main components which can be done with the design of a prototype C-OTEC. Presently, the KEPCO (Korea Electric Power Corporation) Research Institute is conducting a national research project involving the construction of a prototype C-OTEC for a demonstration. It is expected to be operational by the end of 2014. - Highlights: • Plant condensate steam directly Combined Ocean Thermal Energy Conversion is proposed. • C-OTEC can improve efficiency of coastal power plant by improving condenser vacuum. • Additional output and decreased temperature of condenser effluent for power plant. • Feasible at coastal power plant in middle latitude area as well as tropical region. • C-OTEC will be built at Yeongdong power plant in South Korea to validate this study
[en] In this study, a photovoltaic-thermal (PV/T) combi collector was assessed theoretically and experimentally in weather conditions of Sanandaj city in summer, August, 2016 in simple, water, and air modes under unstable conditions from 8:00 a.m. to 18:00 p.m. The air mode with 0.01 kg/s mass flow rate and the water mode with 0.003 kg/s mass flow rate were investigated. The maximum overall efficiencies of the air and water modes were 0.47 and 0.69, respectively, and mean electric power rates generated in the simple, air and water modes were 64.5, 66.7 and 68.2 W, respectively. The energy and exergy means obtained for PV collector during the experiment were found to be 125 and 119 W/m2, respectively. Then, RMSPD, RMSE and MAPE analyses were performed for simulation, showing the accuracy of the model. Finally, the linear correlation coefficients for the parameters “PV collector temperature with solar radiation intensity” and “PV collector temperature with outlet air temperature” were 0.991 and 0.998, respectively, indicating a strong linear correlation between these parameters. - Highlights: • A photovoltaic-thermal combi collector assessed theoretically and experimentally. • Overall efficiency of the system in water, and air modes found to be 0.69 and 0.47. • The energy and exergy obtained for collector found to be 125 and 119 W/m2.
[en] A novel flat heat pipe design has been developed and utilised as a building envelope and thermal solar collector with and without (PV) bonded directly to its surface. The design of the new solar collector has been validated through full scale testing in Cardiff, UK where solar/thermal, uncooled PV and PV/T tests were carried out on three identical systems, simultaneously. The tests showed a solar/thermal energy conversion efficiency of around 64% for the collector with no PV and 50% for the system with the PV layer on it. The effect of cooling on the solar/electrical energy conversion efficiency was also investigated and an efficiency increase of about 15% was recorded for the cooled PV system due to the provided homogenous cooling. The new flat heat pipe solar collector is given the name “heat mat” and, in addition to being an efficient solar collector type, it is also designed to convert a building envelope materials to become energy-active. A full size roof that utilise this new building envelope material is reported in this paper to demonstrate the way this new collector is integrated as a building envelope material to form a roof. A thermal absorption test, in a controlled environment, from the ambient to the heat mat with no solar radiation is also reported. The test has proved the heat mat as an efficient thermal absorber from the ambient to the intermediate fluid that deliver the heat energy to the heat pump system. - Highlights: • A new flat heat pipe PV/T system that can be used as building materials is reported. • The new solar collector enhanced the performance of the PV by about 15%. • The new solar collector is capable of absorbing heat from ambient efficiently. • The new system is efficient from the solar/thermal conversion point of view.
[en] Photovoltaic–thermal water collectors have the ability to convert solar energy into electricity and heat, simultaneously. Furthermore, the combination of photovoltaic–thermal solar collectors with a water cooling system can increase significantly the electrical and thermal efficiencies of the system, which can improve the total thermal efficiency of buildings. In this paper, the findings of six experimental configurations of solar-thermal collectors are presented and analyzed. Five of the solar-thermal panel configurations were implemented with a cooling cycle. Two of the solar-thermal panels were equipped with monocrystalline silicon modules, the other two collectors were equipped with polycrystalline silicone modules, one of the collectors was based on heat pipe technology and was equipped with a cooling system, while the last collector did not include any cooling cycle. The duration of the experiments was four days during the September of 2014 and they were conducted under different solar radiation conditions. The second part of the paper presents the simulation results for five of the solar-thermal panels connected with a cooling water tank (volume of 500 L), a domestic hot water tank (volume 350 L) and a water–water heat pump, in terms of covering the hot water demands of a single family dwelling. The results showed that the hybrid solar collectors would be able to cover approximately 60% of the dwelling's hot water needs for days with low levels of solar radiation, while for days with high solar radiation they could cover the hot water requirements of the family by 100%.
[en] We present a techno-economic analysis of a 17,000–18,000 metric tons per year electrolytic process for producing Mg from MgO with and without out a concentrated solar thermal input. The solar thermal input is delivered via power tower technology and the evaporation and condensation of sodium. Energy requirements for the process at scale were based on thermodynamics and an extrapolation of laboratory measurements of the electrochemical kinetic and mass transport parameters via a finite-element numerical model. While technically possible, integrating a solar thermal input does not make economic sense without crediting avoided CO2 emissions. A solar thermal input reduces energy operational costs from $0.654/kg to as low as $ 0.481/kg, but it also lowers the Mg production rate of the electrolytic cells such that more cells are required to achieve production capacity, which, in turn, increases capital and maintenance costs. The net operational savings are negligible. The estimated operational costs to produce Mg are ∼$2.46/kg. At this cost, the process without a solar thermal input is economically tantalizing vis à vis the current commercial processes for producing Mg, and its CO2 emission level is 46% lower than that of the Pidgeon process, currently the predominant method for producing Mg. - Highlights: • Model of an industrial-scale MgO electrolysis cell using detailed chemical kinetics. • Identify cell voltage at which CF4 forms; it is below industrial operating voltages. • Show that anode effect can be avoided in industrial MgO electrolysis. • Concept couples concentrated solar radiation to industrial MgO electrolysis. • Economic study of MgO electrolysis at scale with and without solar thermal input.
[en] The hydrogen economy is defined as the industrial system in which one of the universal energy carriers is hydrogen (the other is electricity) and hydrogen is oxidized to water that may be reused by applying an external energy source for dissociation of water into its component elements hydrogen and oxygen. There are three different primary energy-supply system classes which may be used to implement the hydrogen economy, namely, fossil fuels (coal, petroleum, natural gas, and as yet largely unused supplies such as shale oil, oil from tar sands, natural gas from geo-pressured locations, etc.), nuclear reactors including fission reactors and breeders or fusion nuclear reactors over the very long term, and renewable energy sources (including hydroelectric power systems, wind-energy systems, ocean thermal energy conversion systems, geothermal resources, and a host of direct solar energy-conversion systems including biomass production, photovoltaic energy conversion, solar thermal systems, etc.). Examination of present costs of hydrogen production by any of these means shows that the hydrogen economy favored by people searching for a non-polluting gaseous or liquid energy carrier will not be developed without new discoveries or innovations. Hydrogen may become an important market entry in a world with most of the electricity generated in nuclear fission or breeder reactors when high-temperature waste heat is used to dissociate water in chemical cycles or new inventions and innovations lead to low-cost hydrogen production by applying as yet uneconomical renewable solar techniques that are suitable for large-scale production such as direct water photolysis with suitably tailored band gaps on semiconductors or low-cost electricity supplies generated on ocean-based platforms using temperature differences in the tropical seas