Results 1 - 10 of 36
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[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] 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] This paper experimentally investigated exergetic performance analysis of vapor compression refrigeration system using R450a as a replacement for R134a at different evaporator and condenser temperatures within controlled environmental conditions. The exergetic performance analysis of the vapor compression refrigeration system with test parameters including efficiency defects in the components, total irreversibility, and exergy efficiency of the refrigeration system was performed. Findings showed that the total irreversibility and exergy efficiency of the vapor compression refrigeration system using R450A refrigerant were lower and higher than R134a by about 15.25–27.32% and 10.07–130.93%, respectively. However, the efficiency defect in the condenser, compressor, and evaporator of the R450A refrigeration system was lower than R134a by about 16.99–26.08%, 5.03–20.11%, and 1.85–15.85%, respectively. Conversely, efficiency defect in the capillary tube of the R450A refrigeration system was higher than R134a by about 14.66–78.97% under similar operating conditions. Overall, it was found that the most efficient component was the evaporator, and the least efficient component was the compressor for both refrigerants.
[en] Turbulent flow of nanofluid inside a solar collector has been presented in the current research. Turbulence mixing has been increased with insertion of new turbolentor. Heat transfer and exergy behavior within the test tube equipped with multi-channel twisted tape elements. Al2O3–water nanofluid flows inside the pipe. Absorber plates are made of aluminum. The scrutinized parameters in current paper are number of revolution (N), diameter ratio (D*), Reynolds number (Re), number of channel (n). Better convection heat transfer can be observed for greater values of diameter ratio. Exergy drop declines with increasing scrutinized parameters due to giving strongly swirling flows with rise of them.
[en] In this paper, a model of irreversible three-electron-reservoir energy selective electron (ESE) cooling device with heat leakage is established. By utilizing the finite time thermodynamics, the optimal performance of the cooling device is studied and the influences of chemical potential differences of electron reservoirs, center energy level of energy filters and heat leakage on the optimal performances are discussed. On the basis of cooling rate and coefficient of performance (COP) analyses, the exergy-based ecological function and figure of merit are proposed as objective functions. The operation properties of ESE cooling device with different objective functions are investigated and the optimal performance region is obtained. Higher cooling rate and COP can both be attained for the ESE cooling device when it is working in the optimal performance region.
[en] In this work, the adaptive neuro-fuzzy inference (ANFIS) system as an artificial intelligence method was used to predict the destruction of exergy in components (compressor, condenser, capillary tube and evaporator) of a vapor compression refrigeration system using a mixture of R134a and LPG refrigerant (consisting of R134a and LPG in a ratio of 28:72 by mass fraction). For this purpose, ANFIS models were developed to predict the destruction of exergy in each component using some experimental data recently published in author previous publication, and the remaining data were used to validate the developed models. It was found that the predictions of ANFIS models are in good agreement with the experimental results and give an absolute fraction of variance in range of 0.996–0.999, a root mean square error in range of 0.0296–0.1726 W and mean absolute percentage error in range of 0.108–0.176%, respectively. The results suggest that the ANFIS models can predict the destruction of exergy in the components of refrigeration system quickly and with high accuracy.
[en] In this work, the thermal performance of single-pass double-duct jet plate solar air heater with various designs of artificial roughness is analyzed by developing a mathematical model. The influence of artificial roughness designs on the performance of the solar air heater is analyzed based on energy and exergy basis, and the results are compared with single-pass single-duct jet plate solar air heater. Further, year-around enviro-economic analysis is carried out for artificial roughness design providing the better performance. The results show that single-pass double-duct jet plate solar air heater with arc-shaped rib roughness produces highest energetic and exergetic efficiency. The results are compared with single-pass single-duct jet plate solar air heater in the form of energetic and exergetic efficiency enhancement ratios, annual overall energy and exergy gain and amount of carbon credit earned. The mathematical model has been validated with analytical and experimental results available in the literature with acceptable deviation. On the basis of numerical calculations, it has been concluded that single-pass double-duct jet plate solar air heater improves annual usual energy and exergy gain by 111.7% and 185.6%, respectively. Further, it reduces 2.11 times of production of CO2 mitigation per year and enhances the revenue of annual carbon credit by 2.85 times.
[en] In this present work, an exergetic efficiency of the solar air heater (SAH) with jet impingement on multiple arc protrusion roughened absorber plate is analytically studied. It is examined out for roughness parameters of relative width ratio (WP/WAP) of 1–5, relative height ratio (eP/dP) of 0.5–2, relative pitch ratio (PP/eP) of 8–12 and angle of arc (αa) of 35°–75°. Performance of SAH based on the second law has been effectively assessed by enumerating the useful exergy gain, irreversibility and losses occurred due to the inefficiency of the system components. Results indicate that the exergetic efficiency has been enhanced by 56.8%. Effects of roughness parameters on exergetic efficiency have been presented based on Reynolds number and temperature rise parameter. The optimized values of roughness parameters are identified, and the maximum exergetic efficiency is found to be 10.5%. Maximum exergetic destruction caused due to temperature difference between absorber plate and Sun is 65.2% at optimized conditions. In order to identify the optimum values of roughness parameters to attain the required temperature rise with maximum exergetic efficiency, design plots have been developed.
[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 temperature rise in photovoltaic cells causing drop in their open-circuit voltage is a serious issue to be dealt with. A wide range of cooling techniques have been proposed by researchers due to its positive results on electrical efficiency during operation. One of the prominent techniques in the field is using a hybrid photovoltaic thermal (PV/T) design which in turns utilizes a working fluid to extract the heat from the collector. Various PV/T designs have been proposed, most prominently nanofluid and nanofluid with nano-PCM-based PV/T. This paper aims to evaluate the two techniques of cooling a grid-connected PV system and examines the systems electrical and combined efficiency, in addition to performing exergy analysis. The two systems are experimentally tested for outdoors conditions in Bangi, Malaysia. The results show the two systems achieving highest electrical exergies of 73 and 74.52 for nanofluid and nanofluid with nano-PCM, respectively. Both systems achieved higher exergies than water-cooled and conventional GCPV.