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[en] In this work, diethyl ether (DEE) and compressed natural gas (CNG) port fuel injection (PFI) was investigated in direct injection (DI) compression ignition engine to determine the performance, combustion, and emission behaviors. In dual fuel mode, DEE and neat diesel were used as fuel energy, whereas in homogeneous charge compression ignition (HCCI) mode, DEE, and CNG were used as fuel energy. The engine behavior was analyzed for different inlet charge temperatures. Exergy analysis has been carried out for analyzing the various availability shares in the engine. The maximum brake thermal efficiency of the engine increased at peak load from 27.31% in neat diesel to 29.12% for dual fuel mode (D + CNG). Hydrocarbon and carbon monoxide emissions were reduced and oxides of nitrogen increased with the inlet charge heating mode. Maximum exergy efficiency was observed as 57.1% in dual fuel operation. The result of this work proves that CNG in dual and HCCI are effective for engine operation.
[en] The exergoeconomic analysis was conducted theoretically for a steam turbine driving vapor compression refrigeration system using R134a, R410a, R407c and R717 in this study. Dual-purpose system was designed by eliminating the expansion valve to fulfill the demand for the cooling load of the steam power plant. Primarily steam turbine was investigated by changing turbine inlet parameters. Afterward, the effect of input parameters of the steam turbine on the cooling load, the coefficient of performance (COP), the exergy efficiency of vapor compression cycle (VCC) and equipment, both the exergy destruction ratio and the exergy efficiency was determined. Among all examined working fluids, R134a was the best candidate from thermodynamic and thermoeconomic viewpoints. The COP values were determined to be 2.73, 2.29, 1.8 and 1.15 for R134a, R410a, R407c and R717, respectively. Also, the exergy efficiencies of the vapor compression refrigeration (VCR) system were found to be 18.61%, 13.93%, 14.97% and 10.01% for R134a, R410a, R407c and R717, respectively. Conversely, the general exergy efficiency of the whole coal-fired plant was 39.1%. As a consequence of integrating VCC, overall exergy efficiencies of the complete system were 39.36%, 39.32%, 39.27% and 39.21% for four different working fluids, respectively.
[en] The performances of solar cells and thermoelectric materials are governed by thermodynamics. The material properties of these have temperature dependence due to thermal expansions of lattices and an effect of electron–phonon coupling etc. The temperature-dependent energy levels has been included in statistical mechanics, naturally requiring a rectification of the second law of thermodynamics with an effective heat. In such a framework, we show that exergy associated with internal energy of isolated systems can be increased in irreversible processes. We furthermore see how the effect of the temperature-dependent energy levels appears in the thermodynamic performance in terms of the second law efficiency. (paper)
[en] In this paper, a thermodynamic analysis of a Sulfur-Iodine thermochemical hydrogen production cycle was performed. At first, a new heat exchanger network configuration was designed by means a heuristic method. Then, an exergy and anergy analysis was carried out in order to analyze the thermal efficiency of the proposed heat exchanger network compared to the reference case. With this study, a reduction of the energy inputs of the process was achieved; being 58.59% for cooling and 52.31% for heating, both lower than the reference case. Regarding the exergy y and anergy calculations for the new heat exchanger configuration, the calculated exergy was 365.202 MJ/K mol-H2 with an anergy of 187.66 MJ/ K mol-H2, being the latest lower than that for the reference case 338.97 MJ/K mol-H2. This means that less energy it is being wasted improving the thermal efficiency of the cycle and reducing the plant operational cost. (author)
[en] This paper provides a conceptual presentation on the integration of existing nuclear power plants with technically robust thermal energy storage solution. Although a more detailed analysis with entire condensate and feed water system integrated to the energy storage solution is required for more accurate analysis, for the conceptual presentation a simpler approach based on energy density and exergy analysis is adopted. Therminol and Dowtherm are commercially available robust technological solutions for this purpose and operate in the temperature range compatible with the existing PWRs. The analysis shows that exergy recovery efficiency is close to 95%, i.e. equal to efficiency proposed using molten salts. The energy density values for these HTFs in this operating range are not expected to create practical challenges and geometrical requirements can be met within the existing nuclear power plants. The energy storage costs with these off the shelf materials already being produced in very large quantities via well established processes are much lower than the projected costs of futuristic grid scale battery solutions. (authors)
[en] Hydrogen is considered to become a main energy vector in sustainable energy systems to store large amounts of intermittent wind and solar power. In this work, exergy efficiency and cost analyses are conducted to compare pathways of hydrogen generation (PEM, alkaline or solid oxide electrolysis), storage (compression, liquefaction or methanation), transportation (trailer or pipeline) and utilization (PEMFC, SOFC or combined cycle gas turbine). All processes are simulated with respect to their full and part-load efficiencies and resulting costs. Furthermore, load profiles are estimated to simulate a whole year of operation at varying loads. The results show power-to-power exergy efficiencies varying between about 17.5 and 43 %. The main losses occur at utilization and generation. Methanation features both lower efficiency and higher costs than compressed hydrogen pathways. While gas turbines show very high efficiency at full load, their efficiency drops significantly during load-following operation , while fuel cells (especially solid oxide) can maintain their efficiency and exceed the combined cycle gas turbine full-load efficiency. Overall specific costs between 245 €/MWh and 646 €/MWh are resulting from the simulation. Lower costs are commonly reached in chains with higher overall efficiencies. Installation costs are identified as predominant because of the low amount of full-load hours. To decrease the energy storage overall costs of the process chains, the options to use revenue generated by by-products such as oxygen and heat as well as changing the system application scenario are investigated. While the effect of the oxygen sale is negligible, the revenue generated by heat can significantly decrease overall costs. An increase of full-load by accounting for an electrolysis base-load to provide hydrogen for vehicles also shows a significant decreases in costs per stored energy down to 151 €/MWh at 2337 h/a full-load hours. The optimization of the exergy efficiency is performed by analysing physical and heat exergy recovery options such as expansion machines in the gas grid, the use of additional thermodynamic cycles (both Joule and Clausius-Rankine), as well as providing heat for steam electrolysis from compression inter-cooling, methanation or stored heat from a solid oxide fuel cell. The analysis shows that at full-load, process chains using solid oxide electrolysis, compressed hydrogen and a combined cycle gas turbine or a solid oxide fuel cells with a heat exergy recovery cycle can reach exergy efficiencies of 47 % and 45.5 %, respectively. A reversible solid oxide cell systems with metal-hydride heat and hydrogen storage can also reach 46.5 % exergy efficiency. The energy storage costs for these processes can be as low as 35 to 40 €/MWh at full-load. At load-following operation the efficiency of the fuel cell systems is expected to increase.