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排序方式: 共有2265条查询结果,搜索用时 203 毫秒
91.
92.
Yazan Taamneh A. E. Kabeel N. Prakash Ravishankar Sathyamurthy Ali J. Chamkha 《亚洲传热研究》2019,48(6):2639-2654
This paper presents the computational analysis of convective heat transfer characteristics, pressure drop, and entropy generation characteristics of Al2O3/water nanofluids in a noncircular duct (triangular) using a single phase approach under a turbulent flow regime. The thermal and pressure drop characteristics of different concentrations of Al2O3 nanoparticles (NPs) and the analysis were carried out in Fluent software using a k‐ε approach under constant wall heat flux around the boundary. The results show that there is an increase in pressure drop and thereby an increase in friction by 20% for the smooth condition. The total pressure drop between the entry and exit section of the duct is increased to approximately 84.2% and 85.6% for a higher Reynolds number (Re = 10 000) compared with that of base fluid. Similarly, the entropy generation of water is increased by 40% as compared with 0.05% and 0.1% Al2O3 NPs. There is also a decrease in entropy generation identified while there is an increase in the Reynolds number. The convective heat transfer of 0.05% and 0.1% nanofluid has a similar trend with increased Reynolds number. The maximum performance is observed at the Reynolds number (Re = 4000) and found to be 1.29 for 0.1% concentration, whereas, the fluid at 0.05% is observed to be at 1.23. At a higher Reynolds number (Re = 10 000) the performance index decreased to approximately 1.19 and 1.25 for 0.05% and 0.1%, respectively. 相似文献
93.
Waste heat is generally dissipated from process water to atmospheric air in cooling towers. In the present study, a novel design is used to extract more amount of heat without any additional energy input by incorporating secondary ambient air in an induced draft wet cooling tower. In addition, more fresh air is induced in the tower from the rain zone, which increases the effectiveness at any value of the water to air flow rate (L/G ratio). Moreover, tower characteristics, range, and evaporation loss were also increased due to the novel design. It is noteworthy that secondary fresh air increases effectiveness, heat rejection, and tower characteristics by 10.12%, 19.65%, and 26.11%, respectively, and decreases approach by 16.32% at 0.55 L/G ratio, 44°C inlet water temperature, 29.7°C dry bulb temperature, and 18.4°C inlet air wet bulb temperature. 相似文献
94.
Alka D. Kamble Vinod K. Saxena Prakash D. Chavan Bhagwan D. Singh Vinod A. Mendhe 《能源学会志》2019,92(4):982-1004
The reactivity of coal and biomass has been evaluated by comparing the optical and chemical changes in feed material prior and after the co-gasification. The proximate, ultimate, GCV, low-pressure N2 sorption isotherm, micropetrography, SEM and EDX spectroscopy analyses are carried out to assess the reactivity of blends of high ash Indian coal and biomass. The relative changes in parameters like surface area, pore size, and pore volume have been correlated with reacted percentage area of coal macerals and cellulose-lignin cellular structures of biomass. The Optimas image processing software is being used to mark the reacted portion of organic constituents and calculated the reactivity percentage. The bottom ash of pure coal has shown the least reacted organic matters, indicating inefficiency of high ash coal due to a large amount of inorganic and inertinite contents that is resisting the oxidation. The reactivity percentage is determined by the petrographic and SEM images, and varies from 36.34 to 99.64% and 6.61–96.22%, respectively. It is summarised that the estimation of percentage alteration of macerals and other micro-organic constituents can be used as one of the practical approaches for the assessment of the reactivity of coal and biomass. The blending ratio 6:4 of coal and press mud has shown the highest reactivity (>99.64%). The values of petrographic and SEM reactivity have shown good correlations with the carbon contents, unreacted vitrinites, mineral matters and biomass remnants. These relations have been taken into account to formulate the proposed petrographic empirically calculated reactivity (RPEC). The focus has also been made to investigate the influence of feed composition on carbon conversion and heating value of the product gas. 相似文献
95.
This article presents a technical review on the effects of thermal loads evolved at the wheel–rail–brake contact interfaces. These dynamic contact interfaces develop heat transfer conditions of widely varied thermal level. Their modeling to identify the sources for a variety of defect formation, observable on wheel tread or rail surface, is very important. The railway system, in general, has to bear axle load, friction load, and thermal load arising from their contact conditions in addition to traction and dynamic loads. The defects arising from the interaction of thermal load and other loadings may be identified as hot spots, shelling, spalling, rolling contact fatigue (RCF), and corrugation. The mechanisms for the formation of such defects are pivoted over the existing thermal environment of dynamic interacting surfaces. This review summarizes the works of early investigations and recent advances in modeling the heat transfer conditions required to estimate the temperature distribution at the contact zone. The heat partitioning method for both drag and stop braking conditions, in the presence of rail chill effect, is emphasized. Thermal gradient, introduced by localized temperature rise in the contact zone, in the presence of variable friction coefficient, promotes the RCF process. These alter the residual stresses in the contact region to cause a structural shakedown, aggravate plastic flow and activates ratchetting phenomenon in rails. The evolution of thermomechanical surface and subsurface fatigue cracks are also discussed for the completeness of this article. The effect of all such defect formation, emerging from thermal loading condition, and their countermeasures for defect mitigation are presented in this review. This abridged technical documentation envisions attracting more research in the area to improve wheel–rail set design and performance standards to extend enhanced safety and comfort to rail transport operation. It is opined that the thermomechanical loading, their effects on promoting defect formation and propagation should be studied in combination instead of the current practice of treating them separately. 相似文献
96.
97.
Ashok Misra Saroj Kumar Mishra J. Prakash 《International Communications in Heat and Mass Transfer》2011,38(8):1110-1118
The present paper envisages the effects of electrification of particles, volume fraction and diffusion of SPM on the boundary layer flow and heat transfer over a semi-infinite flat plate. Irrespective of the particle material density, it has been observed that the range of validity of the solution remains fixed and at x = 2.12 the nature of the profiles of the flow variables changes. Electrification of particles causes the particles to move faster for x < 1.0 and slows down for x > 1.0 but particle temperature increases with increase of M. It has been observed that heat transfer always occurs from the fluid to plate. 相似文献
98.
Pandurang N. Honkhambe Mahesh V. Biyani Nagendra S. Bhairamadgi Prakash P. Wadgaonkar Manikrao M. Salunkhe 《应用聚合物科学杂志》2010,117(5):2545-2552
Two bisphenols, viz., 4,4′‐[1‐(2‐naphthalenyl)ethylidene]bisphenol and 4,4′‐[1‐(2‐naphthalenyl) ethylidene]bis‐3‐methylphenol were prepared by condensation of commercially available 2‐acetonaphthanone with phenol and o‐cresol, respectively. A series of new aromatic polyesters containing pendent naphthyl units was synthesized by phase‐transfer‐catalyzed interfacial polycondensation of these bisphenols with isophthaloyl chloride, terephthaloyl chloride, and a mixture of isophthaloyl chloride/terephthaloyl chloride (50 : 50 mol %). Inherent viscosities of polyesters were in the range 0.83–1.76 dL g−1, while number average molecular weights (Mn) were in the range 61,000–235,000 g mol−1. Polyesters were readily soluble in organic solvents such as dichloromethane, chloroform, tetrahydrofuran, m‐cresol, pyridine, N,N‐dimethylformamide, N,N‐dimethylacetamide, and 1‐methyl‐2‐pyrrolidinone at room temperature. Tough, transparent, and flexible films were cast from a solution of polyesters in chloroform. X‐Ray diffraction measurements displayed a broad halo at 2θ ≅ 19° indicating the amorphous nature of polyesters. Glass transition temperatures of polyesters were in the range 209–259°C. The temperature at 10% weight loss (T10), determined by TGA in nitrogen atmosphere, of polyesters was in the range 435–500°C indicating their good thermal stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
99.
Samia Dabbou Faten Brahmi Ameni Taamali Manel Issaoui Youssef Ouni Mohamed Braham Mokhtar Zarrouk Mohamed Hammami 《Journal of the American Oil Chemists' Society》2010,87(10):1199-1209
The effects of the contents of lipids, pigments, α-tocopherol and phenols were studied in relation to the antioxidant capacity
of five virgin olive oils obtained from five olive cultivars planted in Tunisia (Arbequina, Koroneiki, Leccino, Oueslati and
Chemchali). The antioxidant capacities were evaluated by two different radical scavenging activities: radical scavenging activity
by the DPPH assay (RSA-DPPH) and total antioxidant status by the ABTS test (TAA-ABTS). The highest contents of antioxidant
compounds (75.96, 10.34, 6.32, 15.39 and 241.52 mg kg−1 for oleic acid, O/L ratio, carotenes, chlorophylls and total phenols, respectively) were found for the Koroneiki cultivar
except for α-tocopherol and o-diphenols, which had the highest contents (369 and 160.7 mg kg−1, respectively) in the Leccino and Chemchali cultivars (cvs). Furthermore, the highest antioxidant capacity in virgin olive
oil was observed in the Koroneiki cultivar (0.24 mmol TE kg−1) followed by the Chemchali and Leccino cvs (0.22 and 0.13 mmol TE kg−1) for the TAA-ABTS test. However, the RSA-DPPH activity was higher for the Chemchali cultivar (19.9%) than for the Koroneiki
and Leccino cvs (18.4 and 13.5%, respectively). Correlation between these capacities and the oil composition revealed that
they were mainly influenced by the carotene content, followed by chlorophyll and phenolic contents where the ABTS test was
more pronounced. Then, the antioxidant capacity of the virgin olive oils was correlated with polar components and the lipid
profile which are important for its shelf life. 相似文献
100.
Malik A. Nawaz Shu Fukai Sangeeta Prakash 《International Journal of Food Properties》2018,21(1):1896-1910
The effect of various soaking mediums, viz. water (control), 3% NaCl and 0.2% acetic acid, and without soaking on the physicochemical properties of parboiled selected glutinous (TDK8 and TDK11) and non-glutinous (Doongara) was investigated in the present study. Results showed that the chemistry of soaking had a significant effect on the head rice yield (HRY), grain hardness, crystallinity, color, pasting and thermal properties, textural attributes, and glycemic index of these rice varieties. Soaking with NaCl and acetic acid significantly increased the grain hardness and HRY than control and without soaking treatments. Acetic acid and NaCl soaking significantly affected crystalline regions of starch resulting in reduced crystallinity in X-ray diffraction analysis and thermal endotherms in DSC analysis. NaCl soaking induced swelling of starch granules resulting in high peak and final viscosities. However, acetic acid restricted swelling resulting in reduced peak and final viscosities. NaCl and acetic acid soakings also resulted in increased hardness and adhesiveness of cooked grains than normal water soaked and un-soaked parboiled rice samples. Interestingly, change in textural attributes was prominent in parboiled glutinous rice. The color difference value for fresh parboiled samples was significantly lower for acetic acid soaked samples compared to NaCl soaked and un-soaked samples probably due to bleaching effect of acetic acid. Moreover, parboiling also resulted in significant reduction in glycemic index of glutinous rice. These findings revealed the potential application of parboiling with modified soaking techniques to improve the grain quality. 相似文献