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[en] This work presents a second law analysis efficiency of cogeneration steam turbine unit with backpressure steam turbine. By using the input/product output method is calculated the exergy efficiency of steam turbine unit at four different operational modes. It is obtained the allocation of useful exergy in electricity and released heat to consumers and exergy losses. It is evaluated the impact of referent environment temperature and mass flow from controlled extraction on exergy efficiency.
[en] This paper studies the experimental and exergy analysis of solar still with the sand heat energy storage system. The cumulative yield from solar still with and without energy storage material is found to be 3.3 and 1.89 kg/m2, respectively for 8-h operation. Results show that the exergy efficiency of the system is higher with the least water depth of 0.02 m (mw = 20 kg). Competitive analysis of second law efficiency shows that the exergy efficiency improves the system by 30% than conventional single slope solar still without any heat storage. The maximum exergy efficiency with energy storage material is found as 13.2% and it is less than the conventional solar still without any material inside the basin.
[en] Highlights: • Hourly productivity improves by inserting the reticular porous layer in the basin. • The efficiency improves by inserting the reticular porous layer inside the basin. • The maximum exergy efficiency from the modified system is found as 7.33%. - Abstract: In this paper, an experimental study with the exergy analysis are performed to investigate the application of a reticular porous insert in a single slope solar still for performance improvement. Two single slope solar stills containing conventional and modified by inserting a reticular porous layer are fabricated and experimented together. Two stills have the same dimensions. The porous insert was made up by black sponge rubber. All tests were taken in Semnan with geographical coordinates of 35°33′N, 53°23′E, Iran. Hourly water and glass temperatures, productivity, and efficiency of two stills are measured and evaluated experimentally. Moreover, the exergy efficiencies of the solar stills are obtained and presented. Finally, a cost analysis is performed to investigate the modified still economically. It was concluded that the daily total water productions for one day of the experiment are 3263 and 3829 cc/m2 for the conventional and modified stills, respectively. Accordingly, the modified still produces about 17.35% more distilled water in comparison to the conventional one during one day. Finally, the costs per liter per square meter for the modified and conventional stills are 0.0095 and 0.0108 $/L/m2, respectively.
[en] Highlights: • Advanced exergoeconomic analysis is done on a new helium extraction process. • Cost of exergy destruction and exergy destruction rate are calculated. • Three different strategies are suggested to improve performance of the components. - Abstract: An advanced method of exergoeconomic analysis was applied to a newly developed process configuration used for recovering helium from natural gas. In this process, a three stage propane refrigeration cycle is incorporated to provide a portion of the required refrigeration. Sensitivity analysis was also carried out for exergoeconomic factors and exergy destruction cost of the effective devices. In comparison with the existing processes, the proposed process has better performance in extracting the helium from the feed gas. Based on the results of conventional method, HE-105 and HE-104 heat exchangers have the highest extent of exergy destruction cost equal to 1889.68 $/hr and 1263.58 $/hr, respectively. The outcome of the advanced exergoeconomic analysis suggests that the exergy destruction cost (investment cost) of the compressors is avoidable while it is not true for the heat exchangers. Moreover, the exergy destruction costs induced from the remaining components are not considerable, thus the interactions among the process equipment is not strong.
[en] Highlights: • Single slope solar still coupled with N-identical PVT FPCs has been proposed. • EPBT of the proposed still is found to be 89.90% lower than that of N-PVT-CPC-SS. • An improvement of 27.5% in water production cost over N-PVT-CPC-SS is achieved. • LCCE of N-PVT-FPC-SS is 56.25% higher than that of N-PVT-CPC-SS. - Abstract: This paper communicates the improvement in performance of single slope solar still (SS) by including N identical partially covered photovoltaic thermal (PVT) collectors. Three models have been considered namely, SS included with N identical partially covered PVT flat plate collectors (N-PVT-FPC-SS); SS included with N identical partially covered PVT compound parabolic concentrator collectors (N-PVT-CPC-SS) and conventional SS (CSS). In this work, yearly production of potable water, energy, exergy, energy metrics, cost of distillate output and cogeneration efficiency have been computed for the proposed N-PVT-FPC-SS at 0.14 m water depth under optimized condition for New Delhi, India. Results obtained have been compared with results reported by researchers previously and it has been concluded that exergy based energy payback time is lower by 89.90% and 44.45%; energy production factor is higher by 46.67% and 31.11%; life cycle conversion efficiency is higher by 56.25% and 37.50% and production cost of potable water is lower by 27.05% and 3.20% for the proposed N-PVT-FPC-SS than N-PVT-CPC-SS and CSS respectively. The proposed system can produce potable water on commercial scale and at the same time, it can meet DC electrical power need.
[en] Energy systems are meaningful devices which are based on basic laws of physics to take energy at one end and transform it into another form with optimum efficiency. Scientists, engineers always strive to make systems more efficient and lighter. This motive acts as driving force to bring about new technologies, materials and alternative approaches. Nanofluids are that kind of materials which have revolutionized energy absorbing, transporting and storage systems. Various parameters which are cardinal in thermal performance enhancement are drastically modified when material changes into nanoform. These parameters are thermal conductivity, heat transfer coefficient, optical extinction coefficient, electrical conductivity, viscosity, density, metallic property. When materials changes its phase from bulk to nano, surface to volume ratio changes tremendously. In our experimental analysis we have chosen nanofluids (MgO+CNTs)/H2O Hybrid for evaluating performance of and flat plate solar collector for exergy efficiency, entropy generation and thermal efficiency. Exergy efficiency indicates how system is efficient to convert available energy into useful work. We have gone through preparation of nanofluid along with characterization. Experimental analysis established that at 1% volume concentration and the flow rate 21/min exergetic efficiency (second law efficiency) for (MgO+CNTs)/H2O nanofluid is enhanced by ∼28 % compare to water, ∼13% compare to MgO. Entropy generation rate, which is penalty increases insignificantly at lower concentration for MgO hybrid compare to MgO. But enhancement in exergy efficiency dominates over increment in entropy generation rate. We can conclude that nanofluid based energy transporting systems are more efficient in terms of performance and energy saving. (author)
[en] Highlights: • Dependence of energy and exergy demand for heating of air on outdoor temperature is analysed. • The Pinch method is applied for a HEN of a building’s ventilation system for the first time. • Results show 26% energy and 45% exergy savings after system‘s integration. - Abstract: Intensive use of energy is related to the inefficient use of processes in building engineering systems. In well-insulated non-residential buildings ventilation systems are among the most energy intensive HVAC systems. The main components of an energy (and exergy) efficient ventilation system are heat exchangers. The paper presents the analysis of process integration possibilities in a ventilation system. Only air heating for ventilation purposes is analysed. The method of Pinch technology, mostly used for industrial process integration, is adopted for a ventilation system of a building for the first time. In the paper, several different cases of integration are analysed by using actual BMS data of a shopping centre. The results confirmed that process integration influences the thermodynamic efficiency of the system and that integrated systems consume less energy and exergy in comparison with the non-integrated ones. The case study shows that the seasonal energy demand of the system before integration is 26% higher compared to integrated system and the exergy demand is 45% higher.
[en] Highlights: • A novel absorption system based combined cooling, power, desalination is proposed. • The system can able to provide simultaneous power, cooling and purified water. • Energetic and exergetic performance of combined cycles is analysed. • Highest energy and exergy efficiencies are obtained at 95 °C heat source temperature.
[en] Thermodynamic analysis of a new adsorption cycle recently suggested for upgrading ambient heat (the so-called “Heat from Cold” or HeCol cycle) was performed. The energy and entropy balances at each cycle stage and in each converter component were calculated for the methanol–AC-35.4 activated carbon working pair under conditions of ideal heat transfer. It is shown that useful heat can be obtained only if the ambient temperature is below a threshold temperature. The threshold temperature was calculated based on the Polanyi principle of temperature invariance and was experimentally validated. The specific useful heat can reach 200–300 J/(g adsorbent), which is of practical interest. The use of adsorbents with an abrupt change in the adsorption uptake between boundary isosters of the cycle may lead to further enhancement of the useful heat. For the HeCol cycle, the exergy losses under the conditions of ideal heat transfer are small. At low ambient temperature, the losses in the evaporator, condenser, and adsorber are comparable, whereas at higher ambient temperature the main exergy losses originate from the adsorber heating and cooling.
[en] Highlights: • A holistic numerical compressor simulation is proposed. • An insight into the numerical simulation of the submodels is given. • Special focus is laid on the modeling of the oil influence. • A loss analysis in terms of entropy generation and exergy loss is carried out. - Abstract: The present work deals with a comprehensive investigation of the thermal losses of a hermetic compressor for refrigeration application using numerical methods. In this case numerical models mean full 3d CFD simulation of the refrigerant path using fluid structure interaction to model the valve dynamics, 3d heat conduction in the solid parts of the compressor, 3d CFD simulation of the oil distribution inside the compressor shell to obtain heat transfer coefficients, 3d CFD of the oil flow in the oil pump and mechanical loss determination by solving the Reynolds equation numerically. Validation activities are carried out for both the submodels and the entire thermal model. Furthermore, the compressor losses are described in terms of entropy generation and exergy loss. The results are broken down into losses according to their location. The application of the methodology on a compressor with a cooled valve plate shows that the cooling capacity of the compressor at ASHRAE test conditions can be increased by 2.63% but the compressor COP is only increased by 1.57% due to the rise of the mechanical losses by the viscosity increase.