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[en] Highlights: • A solar-driven Kalina cycle is investigated by advanced exergoeconomic analysis. • The highest exergy efficiencies are related to the separator and turbine with the values. • Rotary machinery have more than 83% avoidable share of exergy destruction rate. - Abstract: A Kalina cycle driven by solar energy resource is evaluated by conventional exergy and exergoeconomic analysis methods. Because conventional exergy analyses isn’t able to give information about costs of the irreversibilities and investment, advanced exergy is investigated. Based on the conventional exergy analyses, the most exergy destruction occurs in a heater with a value of 94.44 kW. Also the highest exergy efficiencies are related to the separator and turbine with the values of 99.67% and 89.81%, respectively. Advanced exergy analyses demonstrates absorber (1.3 $/h) and one of the pumps (0.009 $/h) have the highest and lowest exergy destruction cost rate, respectively. Also the results show turbine (85.88%) and separator (1.105%) have the highest and lowest exergoeconomic factor, respectively. Finally, in order to determine optimum point of the inlet temperatures and pressure ratio of the pumps and turbine (rotary machines), a parametric study is applied at different stages.
[en] In this work, the thermodynamic performance of a single slope solar still with cotton cloth energy storage medium was compared with a simple solar still without energy storage. Two solar stills with similar dimensions (one with cotton cloth energy storage and another without energy storage) were fabricated and investigated its performance under the hot humid climatic conditions of Chennai in India during the summer months of 2017. The performance was evaluated in terms of energy and exergy analysis based on first and second law of thermodynamics, respectively, for 2 mm, 4 mm, 6 mm and 8 mm cotton cloth thickness. The results showed that the maximum energy and exergy efficiency of a solar still was observed to be 23.8% and 2.6%, respectively, for 6 mm cotton cloth thickness. The results confirmed that the cotton cloth regenerative medium has enhanced the still productivity by about 24.1% when compared to the solar still without heat storage.
[en] Thermal energy recovery of pyrometallurgy slags is a worldwide problem that is widely concerned for decades. As chemical recovery method, molten slag cascade recovery method (MS-WHCR) is proposed in this work. As typical endothermic chemical reactions, pyrolysis, gasification, calcination and reforming reactions are applied in this method. Gasification–pyrolysis system, calcination–pyrolysis system, enhanced pyrolysis system (R-SEP) and fixed carbon gasification and sorption-enhanced pyrolysis system (CG–SEP) systems of MS-WHCR method are designed. Based on the first law of thermodynamics and second law of thermodynamics, enthalpy–exergy compass analysis method is applied to analyze the exergy efficiency, consumption of reactants and products of designed MS-WHCR method, compared with traditional water quenched (WQ) method and gravity bed waste heat recovery (GWHR) method. As calculation example, 1000kg copper slag is used in this paper. The results showed that the exergy efficiency and exergy loss of WQ method are 20.7% and −947 MJ respectively. By WQ method, energy quality of molten copper slag is discounted. Copper slag particles should be fast cooled during granulation process. Thus, lots of air is blown in to make enough heat transfer with copper slag particles, which generate some exergy loss. And exergy efficiency of GWHR method is 76.9%. Using chemical endothermic reactions, MS-WHCR method improves the exergy efficiency of molten slag waste heat recovery. There is a slight fluctuation of exergy efficiency by MS-WHCR method for four kinds of systems from 66.6 to 70.1%. Fixed carbon and combustible syngas are acquired by MS-WHCR. And enhanced pyrolysis process in proposed R-SEP and CG–SEP systems improves hydrogen contents in syngas.
[en] Highlights: • Comparative study of cascaded and novel integrated system is presented. • Novel integrated system operates at lower generator temperature of 60 °C than cascaded system. • Advanced exergy analysis results of novel integrated system are presented. • Component priorities for performance improvement of system are represented by Sanky diagram. • 35.2% of total irreversibility can be avoided by improving the efficiency parameters. - Abstract: In present work, a novel configuration of vapor compression-absorption integrated refrigeration system (VCAIRS) is analyzed. Unlike previous vapor compression-absorption cascaded refrigeration system (VCACRS), proposed configuration works at lower generator temperature of 60 °C. Thus, allowing the use of low grade waste heat for its operation. The performance of VCAIRS is also compared with the equivalent vapor compression refrigeration system (VCRS) and VCACRS for the same cooling capacity of 100 kW. The comparative study result shows that electrical energy requirement in VCAIRS is 21.4% more as compared to VCACRS but it is still 63% less as compared to the equivalent VCRS. Further, the second law efficiency of VCAIRS, VCACRS and VCRS are determined to be 27.9%, 32.7% and 18.8%, respectively. Thus, both the VCAIRS and VCACRS are energy and exergy efficient configurations; but, VCACRS results in more energy efficient cooling technology in the foreseeable future as it utilizes heat at lower generator temperature as compared to VCACRS. After the comparative performance study, the exergetic performance of VCAIRS is further explored based on the coefficient of structural bonds (CSB) and advanced exergy analysis methods. Highest CSB of 4.39 is obtained for high pressure solution heat exchanger but its overall contribution in total irreversibility rate is merely 0.2%; whereas, the highest contribution of 17.4% in total irreversibility rate is by compressor 1 but CSB value computed for it is merely 1.73. Further, advance exergy analysis results show that 35.2% of total irreversibility rate of VCAIRS can be avoided by improving the efficiency parameter of components of system.
[en] In this study, thermo-economic optimization of single-pass SAHs (solar air heaters) with obstacles of arcuate shape has been carried out. The research is conducted in order to compare the exergy efficiency of three different types of flat plate SAHs. Also, using NSGA-II (non-dominated sorting genetic algorithm) influencing factors were optimized. The SAHs were two different arcuate obstacles (type II and type III), and the other one had no obstacles (type I). All heater types with single and double glass cover were evaluated. The results showed that the heater with double glass cover and the obstacles (type III) had the highest function in both economic and exergetic aspects. Based on the NSGA-II results, collector with flow rate, area and the outlet temperature of 0.017 kg s−1, 2.6 m2 and 78 °C, respectively, had the best performance.
[en] Highlights: • Irreversible degree of heat transfer in organic Rankine cycle (ORC) is proposed. • Theoretical model of irreversible degree is built based on a trapezoidal cycle (TPC). • Thermodynamic relation between irreversible degree and cycle performance is built and studied. • Model of working fluid with linear saturation line is proposed to study the general principles of ORC. - Abstract: Irreversible degree of heat transfer in organic Rankine cycle (ORC) is proposed in this paper. Based on a trapezoidal cycle (TPC) and its theoretical model, the model and mathematic formulas of irreversible degree of heat transfer is built. Thermodynamic relation between irreversible degree and cycle performance (thermal efficiency, net power output and exergy efficiency) is built and studied, which can be applied to the coupling optimization between cycle performance and heat transfer processes. Similar to net power output, there exists a kind of shift-curve of irreversible degree and the corresponding shift-temperature of heating fluid for working fluids, which indicates the shift of irreversible degree from having optimum condition with a minimum to monotonic decrease with heating fluid temperature. The range of irreversible degree and range of cycle performance according to irreversible degree are obtained respectively. Moreover, a model of working fluid with linear saturation line is proposed to study the general thermodynamic principles of TPC (or ORC) theoretically without the restriction of actual working fluids.
[en] This paper highlights an investigation on the comparative analyses of exergetic performance with optimum volume concentration of hybrid nanofluids in a plate heat exchanger (PHE). Different types of hybrid nanofluids (Al2O3 + MWCNT/water, TiO2 + MWCNT/water, ZnO + MWCNT/water, and CeO2 + MWCNT/water) as coolant have been tested. Proportion of 0.75% of nanofluid has been found to be the optimum volume concentration. The requisite thermal and physical properties of the hybrid nanofluids were measured at 35 °C. Various exergetic performance parameters have been examined for comparing different hybrid nanofluids. The highest reduction in exergy loss of CeO2 + MWCNT/water hybrid nanofluid has been obtained at a concentration of about 24.75%. Entropy generation decreased with the increase in volume concentration. The results established that CeO2 + MWCNT/water hybrid nanofluid can be a promising coolant for exergetic performances in a PHE. (paper)
[en] Highlights: • Exergy efficiencies are classified and their limitations are discussed. • An exergy efficiency with generalized formulas is suggested to handle physical and chemical changes. • A complex LNG process (DMR) is optimized and evaluated by the exergy efficiencies. • The new exergy efficiency delivers accurate results for systems having changes in chemical exergy. • Recommendations are also made for a proper selection of exergy efficiency for various process types. - Abstract: In this paper, exergy efficiencies, which are effective performance parameters for cryogenic processes, are categorized based on their exergy decomposition levels. However, the existing efficiencies are not standardized for a variety of unit operations. Thus, the extension of the exergy transfer effectiveness (ETE) has been suggested with a general mathematical expression. The extended ETE is defined by decomposing both thermo-mechanical and chemical exergy to the chemical component level. A case study with a complex natural gas liquefaction process and its optimization has also been performed. The results indicate that the extended ETE brings consistent and accurate results for all types of units, also properly reflecting the changes in process performance after optimization. Other efficiencies, however, struggle to measure the performance improvement for some equipment, even showing decreases in their efficiency values.
[en] Highlights: • A conical and a spiral cavity receiver are examined for a solar dish collector. • The analysis is optical, thermal and exergetic for different operating conditions. • It is found that the conical design is more efficient than the spiral one. • The optical efficiency of the conical design is 1.38% higher than the spiral one. • The thermal efficiency enhancement with the conical design is 5.63% at 100 °C. - Abstract: The objective of this work is to compare two cavity receivers for a solar dish concentrator. The spiral and the conical cavities are investigated using a developed thermal model. The analysis is optical, thermal and exergetic for different operating temperatures and flow rates. The developed thermal model is combined with an optical tool in order to simulate properly the solar dish collector and it is validated for the case of the spiral absorber with experimental results. Every receiver is separated in the different coil and every coil is simulated separately in order to increase the model accuracy. Totally, 13 coils are used for the spiral design and 11 for the conical design. The location of the receiver in every case is optimized in order to achieve maximum optical efficiency. The results show that the conical design leads to a 1.38% increase in the optical efficiency due to the increased intercept factor. The thermal efficiency enhancement with the use of conical design is found to be 5.63% at 100 °C and 40.45% at 200 °C, while the exergy efficiency enhancement 6.67% at 100 °C and 42.06% at 200 °C.
[en] Highlights: • Two novel geothermal-based systems are proposed and assessed exergo-economically. • Multi-objective optimization is conducted to compare the proposed systems with the basic ORC. • Exergy efficiency of the proposed systems is higher than that of the basic ORC by 21.9% and 12.7%. • Specific product cost for the proposed systems is lower than that for the basic ORC. - Abstract: The aim of this study is to enhance the performance of a geothermal-based organic Rankine cycle by proposing two novel systems in which some part of the waste heat is recovered employing thermoelectric generator for power and/or hydrogen production (using proton exchange membrane electrolyzer). Accordingly, two novel systems are proposed and analyzed along with the basic organic Rankine cycle (configuration (a)). In the first proposed system, some part of the waste heat is recovered by employing thermoelectric generator (configuration (b)), while in the second one the additional power generated by thermoelectric generator is used in the proton exchange membrane electrolyzer for hydrogen production (configuration (c)). The performances of the proposed systems are investigated and compared with that of the basic cycle from energy, exergy and exergoeconomic viewpoints and are optimized using genetic algorithm via a multi-objective optimization strategy. The results indicate that, at the best solution point obtained from multi-objective optimization, the exergy efficiencies of the proposed systems (configurations (b) and (c)) are higher than that of the basic organic Rankine cycle by 21.9% and 12.7%, respectively. Furthermore, another interesting result is found which reveals that the specific product cost for the proposed configurations (b) and (c) is lower than that for the basic organic Rankine cycle, despite the higher total cost rate for the proposed configurations.