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[en] A first model for a hydrogen liquefaction prototype laboratory unit has been developed. The process is based on using a mixed component refrigerant (MCR) process for pre-cooling. The process also includes an implementation of ortho para conversion. By simulations it has been shown that this process have potential to improve the exergy efficiency for the liquefaction process and thereby also the energy requirements for hydrogen liquefaction. One of the key points in the design work has been to find a refrigerant that is sufficiently wide-boiling and at the same time not freezing at the low temperature end. The goal has been to reach sub-cooling to below 75 K without freezing out any component of the MCR. (authors)
[en] In Pico Truncado, Santa Cruz, Patagonia, Argentina, a wind farm with 2,4 MWatt is already installed. Greenhouse gas emissions could be reduced about seven thousand tons/year. A Demo Plant for electrolytic Hydrogen production was officially inaugurated on December 2005. Additionally, UNIDO-ICHET proposed at Koluel Kayke village, close to Pico Truncado, progressive replacement of present energy system by Wind, Water, Electricity and Hydrogen, thus covering all kind of final energy requirements. Natural gas and liquid fuels replacement by Hydrogen will be used for homes, productive micro enterprises, vehicles and general machinery. Demo experiences with fuel cells, ICE electric generator, catalytic heaters, compressors, heat recovery and exergy improvement are in progress. Human resources training and diffusion of Clean Hydrogen Energy Culture to general public, mostly scholars, are of great interest. (authors)
[en] Exergy analysis is a powerful tool for developing, evaluating and improving an energy conversion system. However, the lack of a formal procedure in using the results obtained by an exergy analysis is one of the reasons for exergy analysis not being very popular among energy practitioners. Such a formal procedure cannot be developed as long as the interactions among components of the overall system are not being taken properly into account. Splitting the exergy destruction into unavoidable and avoidable parts in a component provides a realistic measure of the potential for improving the thermodynamic efficiency of this component. Alternatively splitting the exergy destruction into endogenous and exogenous parts provides information on the interactions among system components. Distinctions between avoidable and unavoidable exergy destruction on one side and endogenous and exogenous exergy destruction on the other side allow the engineer to focus on the thermodynamic inefficiencies that can be avoided and to consider the interactions among system components. The avoidable endogenous and the avoidable exogenous exergy destruction provide the best guidance for improving the thermodynamic performance of energy conversion systems.
[en] Solar thermal is a promising renewable energy supplying technology that is being introduced slowly in industrial activities. Integration of solar thermal energy in a complex process, in combination with other energy provision devices, must be evaluated carefully, in order to obtain its maximum capacity and performance. This study tackles the integration of the thermosolar technology in a dairy process, sited in a climatic zone where diffuse irradiation is the meaningful one, based on two well developed thermodynamic tools: pinch and exergy analysis. Both tools have been utilized in the context of a low and middle temperature for the production of hot water for the steps of the dairy process. A combined implementation of both methodologies, helped by economical estimation, provides a powerful tool that allows finding the best integration of thermosolar and, by this, taking substantial design decisions. - Highlights: ► Integration of solar thermal energy in an industrial process was assessed. ► Pinch and exergy analysis were used to determine the optimal energy supply configuration. ► Solar thermal energy reduces the fossil energy demand with a moderate investment.
[en] In this paper, a large MSF distillation plant in the gulf area is analyzed thermodynamically using actual plant operation data. Exergy flow rates are evaluated throughout the plant, and the exergy flow diagram is prepared. The rates of exergy destruction and their percentages are indicated on the diagram so that the locations of highest exergy destruction can easily be identified. The highest exergy destruction (77.7%) occurs within the MSF unit, as expected, and this can be reduced by increasing the number of flashing stages. The exergy destruction in the pumps and motors account for 5.3% of the total, and this also can be reduced by using high efficiency motors and pumps. The plant is determined to have a second law efficiency of just 4.2%, which is very low. This indicates that there are major opportunities in the plant to reduce exergy destruction and, thus, the amount of electric and thermal energy supplied, making the operation of the plant more cost effective
[en] The exergy analysis (availability or second law analysis) is applied to the photovoltaic thermal solar collector. Photovoltaic thermal collector is a special type of solar collector where electricity and heat are produced simultaneously. The electricity produced from the photovoltaic thermal collector is all converted into useful work. The available quantity of the heat collected can readily be determined by taking into account both the quantity (heat quantity) and quality ( a function of temperature) of the thermal energy. Therefore, using the concept of exergy allows heat produced from the thermal collector and the electricity generated from the photovoltaic cells to be compared or to be evaluated on the basis of a common measure such as the effectiveness on solar energy collection or the total amount of available energy. In this paper, the effectiveness of solar energy collection is called combined photovoltaic thermal exergy efficiency. An experimental setup of a double pas photovoltaic thermal solar collector has been deigned, fabricated and tested. (author)
[en] Endothermic catalytic reactions of 2-propanol dehydrogenation, performed in both batch-wise and flow-type reactors, were able to proceed by heating at 90 C quite efficiently. Moreover, it was released for the 2-propanol conversion to exceed the limit of chemical equilibrium for hydrogen evolution, the driving force of which was ascribed to a thermodynamic coupling between the heat flow under a temperature gradient and the mass transfer of de-sorbing products at the interface of the superheated catalytic sites and the boiling solution. Hydrogen storage with use of the reaction pair of 2-propanol dehydrogenation/acetone hydrogenation should be evaluated, particularly because it requires low exergy consumption in contrast to compressed or liquefied hydrogen. (authors)
[en] Highlights: ► A new spectral decomposing approach has been introduced for concentrating PVs. ► Both heating and electrical energy have been gained by CPVCS. ► The full spectrum of solar energy has been utilized by the novel CPVCS. ► The energy and exergy efficiencies were found as 7.3% and 1.16% respectively. ► The energy production cost has been stated as 6.37 $/W. - Abstract: In the present study, a novel Concentrating Photovoltaic Combined System (CPVCS) based on the spectral decomposing approach is introduced, modeled, tested experimentally and evaluated thermodynamically and economically. In this study, energy and exergy analyses of the system have been evaluated, economical analysis has been performed and the experimental results have been compared to data obtained by the control system. As a result, energy efficiencies of concentrator, vacuum tube and overall CPVCS have been determined to be 15.35%; 49.86%; and 7.3% respectively. Similarly the second law (exergy) efficiencies of concentrator, vacuum tube and overall CPVCS are 12.06%; 2.0%; and 1.16% respectively. The cost of energy production has been stated as 6.37 $/W and it is predicted that this value could be decreased by improving the system performance
[en] The evaporative gas turbine cycle is a new high efficiency power cycle that has reached the pilot plant testing stage. The latest configuration proposed for this cycle is known as part flow evaporative gas turbine cycle (PEvGT) in which humidification is combined with steam injection. Having advantages of both steam injected and humid air cycles, it is regarded as a very desirable plant for future. In this paper the exergy equations have been added to the mathematical model. Then exergy analysis and optimization of the PEvGT cycles: PEvGT and PEvGT-IC have been done. This study show that the maximum exergy destruction rate related to combustion chamber in both cycles. The exergetic optimization shows, the maximum first and second efficiency occur in the highest values of part-flow humidification rate. (author)
[en] Ground-source heat pump systems (GSHPSs), also referred to as geothermal heat pump systems (GHPSs), have been widely used in residential and commercial buildings for years due to their outstanding energy utilization efficiencies. In this study, an energy and exergy modeling of solar assisted ground-source heat pump systems for residential applications is presented for system analysis and performance evaluation. In this regard, the performance of a solar assisted ground-source heat pump heating system, installed in Solar Energy Institute of Ege University, Izmir, Turkey, is evaluated based on the actual operational data to show how energy and exergy efficiencies values change with the system. The average heating coefficient of performances (as energy efficiencies) of the solar assisted ground-source heat pump (GSHP) unit and the overall system are obtained to be 2.64 and 2.38, respectively. The average exergy efficiency of the system is determined to be 67.7%. (author)