Turbulent drag reducing characteristics of CTAC/NaSal aqueous solution (CTAC had same mass concentration with NaSal.) were investigated in a two-dimensional channel of 30 mm height and 375 mm width, which was made of ...
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Turbulent drag reducing characteristics of CTAC/NaSal aqueous solution (CTAC had same mass concentration with NaSal.) were investigated in a two-dimensional channel of 30 mm height and 375 mm width, which was made of transparent acrylic resin. The measured drag reduction data were scaled up by using Hoyt's scaling method and were compared with other reported drag reduction data for different channel sizes. It could be concluded that both the critical temperature and critical Reynolds number at which turbulent drag reduction of surfactant solution occurred increased with concentration. There was a maximum drag-reduction about 60% for the measured CTAC/NaSal solutions. The Hoyt's scale-up method correlated well the experimental data for different channel heights when the SIS (shearing induced structure) was established very well in surfactant solutions.
In the petroleum refining industry, the fossil fuel used by the atmospheric and vacuum distillation units takes large proportion to the plant-self energy consumption. It is necessary to optimize the system for the ene...
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In the petroleum refining industry, the fossil fuel used by the atmospheric and vacuum distillation units takes large proportion to the plant-self energy consumption. It is necessary to optimize the system for the energysaving consideration. In this study, the exergy analysis method was utilized to optimize the gas collecting system. It is found that, the water bath furnace was a weak link, so we must improve inlet temperature of the fuel and reduce the number of excess air to enhance the economy of the system and reduce the exergy loss.
Electrospinning has been proved to be a versatile and effective method for manufacturing micro-scale to nano-scale fibers continuously. In this article, CdS/ZnO core/shell nanofibers were prepared successfully by the ...
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ISBN:
(纸本)9781118205976
Electrospinning has been proved to be a versatile and effective method for manufacturing micro-scale to nano-scale fibers continuously. In this article, CdS/ZnO core/shell nanofibers were prepared successfully by the typical single-nozzle electrospinning, with subsequent simple thermal decomposition. The SEM and TEM results indicated that core-shell fibers with a diameter of 200-350 nm and shell thickness of 50nm were obtained when PVP/zinc acetate/cadmium acetate/thiocarbamide composite nanofibers were calcined at 480°C for 4h. The EDS analysis results showed that the core fiber is CdS and the shell layer is ZnO. Hydrogen evolution measurements from photocatalytic water splitting using the ZnO/CdS core-shell nanofibers as photocatalyst were carried out. The ZnO/CdS core-shell nanofibers demonstrate a much higher ability for H 2 evolution than that of sole CdS or ZnO. The highest H2 evolution rate was up to 354 μmolh-1 g-1.
Mass exchange network (MEN) is an important part of chemical process. Many methods have already been developed for MEN synthesis to increase the producting efficiency, such as minimizing material consumption, optimizi...
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Mass exchange network (MEN) is an important part of chemical process. Many methods have already been developed for MEN synthesis to increase the producting efficiency, such as minimizing material consumption, optimizing total annualized cost and so on. However, the energy utilization of MEN has scarcely been studied before. This paper introduces exergoeconomic analysis to MEN synthesis. The integrated analysis of energy and economic factors could provide a better guidance for production operation. The most important merit of exergoeconomic analysis is that the MEN synthesis can be further integrated with the energy exchange networks, such as heat and pressure exchange networks. Therefore, the feasibility of exergoeconomic method used in MEN synthesis is studied. A case study of water network synthesis is carried out to reveal the feasibility of exergoeconomic analysis in optimizing MEN. The optimization turns out to be a mixed integer nonlinear programming (MINLP) problem because of the multi-objective and multiconstraint factors. Genetic algorithm (GA) is employed to get a globally optimal solution based on MATLAB program. The calculation shows that the result of MEN exergoeconomic analysis is basically consistent with that of waste minimization, with a little difference according to the energy and economic factors. Therefore, exergoeconomic analysis is proved to have a good performance in solving mass exchange network synthesis problems.
Instantaneous detailed flame front structure of syngas turbulent premixed flames was investigated and compared to that of CH4/air flames. Results show that the flame front of turbulent premixed flames at high pressure...
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Instantaneous detailed flame front structure of syngas turbulent premixed flames was investigated and compared to that of CH4/air flames. Results show that the flame front of turbulent premixed flames at high pressure is a wrinkled flame front with small scale convex and concave structures superimposed with large scale flame branches. The convex structures are much more frequent than the concave ones on flame front which reflects a general characteristic of the turbulent premixed flames at high pressure. The syngas flames possess much wrinkled flame front with much smaller fine cusps structure compared to that of CH4/air flames and the main difference is on the convex structure. The effect of turbulence on the general wrinkled scale of flame front is much weaker than that of the smallest wrinkled scale. The general wrinkled scale is mainly dominated by the turbulence vortex scale, while, the smallest wrinkled scale is determined by the flame intrinsic instability. The effect of flame intrinsic instability on flame front of turbulent premixed flame is mainly on the formation of a large number of convex cusps structure propagating to the unburned reactants and enlarge the effective contact surface between flame front and unburned reactants.
Although much research has been conducted on investigating the flow boiling heat transfer of low saturation temperature refrigerants, there are few experimental data and theory about the flow boiling heat transfer of ...
Although much research has been conducted on investigating the flow boiling heat transfer of low saturation temperature refrigerants, there are few experimental data and theory about the flow boiling heat transfer of high saturation temperature organic mixture which exists widely in the petrochemical industry. To investigate the characteristics of flow boiling heat transfer of high saturation temperature organic mixture, experiments of glycol-water solution flow boiling in a vertical porous surface tube and a vertical smooth tube are conducted. Test tubes are uniformly heated by electrical current with a heated length of 2,000 mm. The mass flux in the experiment ranges from 500 to 1,500t⋅h−1 and the heat flux on test tubes ranges from 10 to 40 kW⋅m−2. The flow boiling heat transfer coefficients and two-phase frictional pressure drops of the two types of tubes are obtained and compared. The results indicate that: the flow boiling heat transfer coefficient in the porous surface tube is 3.8∼5.7 times of that in smooth tube and the pressure drop of the porous surface tube is 0.99∼1.007 times of that in the smooth tube. The physical mechanisms of the enhanced heat transfer characteristics of flow boiling in the porous surface tube are analyzed. By the regression analysis of the experimental data, correlations predicting the flow boiling heat transfer coefficient and pressure drop of glycol-water solution within the error range of ±20% are established. The experimental results can be used to guide the design of heat exchange equipment using the porous surface tube as heat transfer elements under these test conditions.
The wind velocity plays a crucial role in the operation characteristic of indirect cooling tower. In this paper a 2×330MW vertical arrangement indirect air-cooled system was taken as research object, and numerica...
The wind velocity plays a crucial role in the operation characteristic of indirect cooling tower. In this paper a 2×330MW vertical arrangement indirect air-cooled system was taken as research object, and numerical simulation method was used to analyze the relative influence of the wind speed, ranging from 4m/s to 18m/s, on the outlet water temperature of cooling tower, the outlet air temperature of radiator, the facing wind speed of the fan segment and on the outlet air speed of the cooling tower. The result shows that the impact of the natural wind speed on the cooling tower efficiency varies greatly and this impact increases as the wind speed increases.
Strong wind has a significant impact on the heat radiation of the air-cooling system. In this research, a numerical calculation model of 2×1000MW horizontally arranged air-cooling tower is established to simulate...
Strong wind has a significant impact on the heat radiation of the air-cooling system. In this research, a numerical calculation model of 2×1000MW horizontally arranged air-cooling tower is established to simulate the flow distribution and heat exchanging capability of three different structures-horizontally-arranged indirect air-cooling tower, tower with guide wall outside, and tower with a cross wall inside-under high-speed wind and extreme-speed wind conditions. The result reveals that the structure with the guide wall outside the tower only works under strong wind condition while the structure with cross wall inside shows the anti-wind capability under both high-speed wind and extreme-speed wind conditions.
In present experiment, the vapor mixture with different velocities (2m⋅s−1, 4m⋅s−1) and different ethanol mass fraction (0.5%, 1%, 2%, 5%, 10%, 20%, 50%) flew through vertical micro-tube and condensed on the outer tub...
In present experiment, the vapor mixture with different velocities (2m⋅s−1, 4m⋅s−1) and different ethanol mass fraction (0.5%, 1%, 2%, 5%, 10%, 20%, 50%) flew through vertical micro-tube and condensed on the outer tube surface at pressure 31.16kPa, 47.36kPa. The condensation modes were observed by CCD camera, and the characteristics of the heat transfer coefficients versus the vapor-to-surface temperature differences for different experimental conditions were obtained. The condensation heat transfer coefficients of vapor mixture decrease with the vapor concentration increasing. The maximum peak value of heat transfer coefficients, up to 39 kW⋅m−2⋅K1, which was about 3-4 times greater than that of steam, appeared when the ethanol mass fraction was 2%. A heat transfer coefficient correlation including the effects of all the tested parameters is proposed by using the multiple linear least squares method based on the experimental data. The calculated values agreed well with the experimental data and the deviations between them were from −20% to 20%.
With increasing environmental deterioration and energy demand, studies on new alternative fuels have been attracting more attention. N-pentanol is a five carbon, straight-chain alcohol, which can be produced through n...
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ISBN:
(纸本)9781627488426
With increasing environmental deterioration and energy demand, studies on new alternative fuels have been attracting more attention. N-pentanol is a five carbon, straight-chain alcohol, which can be produced through natural microbial fermentation and/or engineered microorganisms. It has many advantages over lower carbon alcohols, including higher energy density, lower vapor pressure and better fuel compatibility. In this study, a detailed reaction mechanism of n-pentanol, on the basis of a previously proposed n-butanol mechanism, is generated using the open-source software Reaction Mechanism Generator (RMG). High temperature chemistry of the mechanism was validated against recently published laminar flame speeds and ignition delays. Encouraging results between simulations and experiments were observed under most conditions. Simulations were also conducted using a recently developed n-pentanol oxidation mechanism (NUI model) by Heufer et al. For lean mixtures, the two mechanisms show similar results, while the RMG model yields better predictions for rich mixtures and at an elevated pressure. Reaction pathways and sensitivity analysis reveal the key differences between the two mechanisms in terms of intermediates formed and fuel consumption.
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