Supersonic ejectors involve very complex phenomena such as interaction between supersonic and subsonic flows, shock trains, instabilities, which strongly influences the performance of supersonic ejector. In this study...
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Supersonic ejectors involve very complex phenomena such as interaction between supersonic and subsonic flows, shock trains, instabilities, which strongly influences the performance of supersonic ejector. In this study, the static pressure distribution along the ejector wall and Mach number distribution along the axis are used to investigate the internal flow field of supersonic ejector. Results indicate that when the back pressure is much less than the critical back pressure, there are two series of shock trains, and the change of the back pressure will not affect the flow field before the effective area section, so the entrainment ratio would remain constant. The second shock train moves further upstream and is combined with the first shock train to form a single shock train as the back pressure rises. When the back pressure is greater than the critical back pressure, the position of the shock train, the static pressure at its upstream and the entrainment ratio, will be affected. The effective area section in the mixing tube is obtained. The effective area section position moves downstream with the increase of the primary flow pressure, while it moves upstream with the increase of the secondary flow pressure. The entrainment ratio shows inversely proportional relationship with the effective section position. Besides, the first shock train length increases with the increase of primary flow pressure or secondary flow pressure. The critical back pressure represents direct proportional relationship to the first shock train length.
A flow calorimeter based on energy conservation was constructed for experimental measurements of isobaric specific heat capacity. The relative expanded uncertainty of isobaric specific heat capacity was identified as ...
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A flow calorimeter based on energy conservation was constructed for experimental measurements of isobaric specific heat capacity. The relative expanded uncertainty of isobaric specific heat capacity was identified as 2.32% (coverage factor k = 2). In the peak region, the relative expanded uncertainty of isobaric specific heat capacity increased to 7.10% (coverage factor k = 2). To verify the accuracy and reliability of the flow calorimeter, pure water and different mole-fraction binary mixtures of n-pentane and acetone were tested in the liquid and vapor phases. The maximum absolute deviation and average absolute deviation were 1.42% and 0.51%, respectively. The isobaric specific heat capacity of emulsified kerosene with different mass fractions was measured at temperatures ranging from 301 K to 878 K and at pressure p = 3 MPa. The effects of different mass frictions of water and temperature on the isobaric specific heat capacities were analyzed in detail. Finally, the isobaric specific heat capacity of RP-3 was compared with that of emulsified kerosene.
Introducing a negative preswirl at the upstream of annular gas seals has been considered as an effective way to improve the system stability. This paper demonstrates a stability enhancement approach for a short labyri...
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Introducing a negative preswirl at the upstream of annular gas seals has been considered as an effective way to improve the system stability. This paper demonstrates a stability enhancement approach for a short labyrinth seal using positive preswirls. The static and dynamic characteristics of the labyrinth seal with various blade numbers (5, 10, 15), inlet preswirl ratios (-0.3, -0.15, 0, 0.15, 0.3) were studied. Results show that the inlet preswirl ratio has a dramatic effect on the circumferential location of the high-pressure spot for each seal cavity, particularly for the first cavity. The inlet preswirl ratio has opposite effects on the system stability due to the difference of high-pressure spot locations between the first cavity and the others. An increasing positive inlet preswirl could improve the system stability for the labyrinth seal with fewer blades (e.g. 5 blades). Its characteristics is mainly dominated by the first seal cavity. For the labyrinth seal with 10 blades, the system characteristics shows slight dependency on the inlet preswirl ratio. For the labyrinth seal with more blades (e.g. 15 blades), the negative inlet preswirl still increases the system stability, which agrees with the conventional conclusion. The paper provides a deeper understanding on the stability improvement of the labyrinth seal.
A sub-channel analysis code, ATHAS-02, based on a two-fluid two-field model is developed in this study. The semi-implicit numerical solution scheme based on the staggered mesh system is adopted to get the finite diffe...
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A sub-channel analysis code, ATHAS-02, based on a two-fluid two-field model is developed in this study. The semi-implicit numerical solution scheme based on the staggered mesh system is adopted to get the finite difference equations. A pressure-velocity coupling algorithm is applied to iteratively solve the finite-difference equations. Meanwhile, preliminary validation studies are performed based on the in-tube subcooled boiling experiments, the GE 9-rod bundle experiments and the Studsvik bundle experiments. It is found that the predicted results agree well with the experimental data.
Although numerous studies on CO2 gasification during coal char combustion have been documented, the effects of CO2 gasification on high-temperature carbon oxidation, which is important for evaluation of carbon convers...
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Although numerous studies on CO2 gasification during coal char combustion have been documented, the effects of CO2 gasification on high-temperature carbon oxidation, which is important for evaluation of carbon conversion during pulverized coal combustion under oxy-fuel and flue gas recirculation conditions, are unclear. Thus, the char conversion characteristics at various contents of O-2 and CO2 were studied in a drop-tube furnace at 1373 K. Due to the cumulative effects of CO2 gasification, which can not only suppress carbon conversion due to endothermicity but also consume part of carbon directly, there exists a minimal carbon conversion point around the CO2 content of 9-13 vol%, where the growth of promotion effect with CO2 content catches up with the suppression effect, and an inflection point around the CO2 content of 17-25 vol%, where the promotion effect of the direct gasification reaction on carbon consumption surpasses the suppression effect. Increasing O-2 shifts both points towards high CO2 contents, whereas increasing combustion gas temperature decreases the values. A mathematical formula including oxidation, effect of gasification on oxidation, and CO2 gasification, is presented, which gives well prediction on high-temperature carbon conversion. With increasing CO2 content, the reduction degree of CO2 gasification on oxidation rate increases, and the synthesis oxidation rate slightly decreases, whereas there always exists a minimal point for gasification rate, gross carbon conversion rate, and gasification weightiness. With increasing O-2 content, the oxidation rate, reduction degree of CO2 gasification on oxidation rate, and gross carbon conversion rate increase;the gasification rate increases below the minimal point, whereas decreases above the minimal point;the gasification weightiness decreases. Combustion gas temperature shows positive effect on all abovementioned parameters. The results derived here provide meaningful guidelines for practical appl
Ferredoxin I (FdI), encoded by fdxN gene, is proved to be the main electron donor of nitrogenase for hydrogen production. In this work, fdxN gene overexpression was implemented in a mutant MHY01, which was constructed...
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Ferredoxin I (FdI), encoded by fdxN gene, is proved to be the main electron donor of nitrogenase for hydrogen production. In this work, fdxN gene overexpression was implemented in a mutant MHY01, which was constructed by inserting fdxN gene into the hupSL region in Rhodobacter sphaeroides HY01 genome. Its photo-fermentative H-2 production performance was studied. The results showed that the expression level of fdxN and nitrogenase activity in MHY01 (hupSL::fdxN) were enhanced by 177% and 61.7% respectively compared with that of wild type HY01. Using 25 mM acetate and 34 mM butyrate as carbon source and 6 mM L-glutamate as nitrogen source, the maximum H-2 production rate was 156.1 mL/(L.h.), which was increased by 50.7% compared with that of HY01. The maximum H-2 production rates of MHY01 were enhanced by 30.0%, 52.5% and 50.7% compared with those obtained from HY01 at the inoculation size of 5%, 10% and 15% respectively. The results suggested that overexpressing fdxN could enhance the nitrogenase activity and H-2 production performance of purple non-sulfur bacteria. The abundancy of ferredoxin I might limit the efficiency of electron transfer flux associated with the biohydrogen production process. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
HPR1000 (Hua-long Pressurized Reactor) Nuclear power Plant is a type of third generation advanced PWR developed in China. In this study, a home-made multi-compartment containment code, ATHROC (Analysis of Thermal Hydr...
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HPR1000 (Hua-long Pressurized Reactor) Nuclear power Plant is a type of third generation advanced PWR developed in China. In this study, a home-made multi-compartment containment code, ATHROC (Analysis of Thermal Hydraulic Response Of Containment), was developed to analyze the thermal-hydraulics and hydrogen behaviors in HPR1000 containment. Two types of bulk fluids, the atmosphere bulk fluid and the pool bulk fluid, were used to model the transient behaviors of multiphaseflow. The atmosphere bulk fluid consists of steam, noncondensables and homogeneously dispersed liquid droplets. The code contains comprehensive models, including flow model, heat and mass transfer model, engineering safety feature model, etc. A plume model was implemented to assess buoyancy driven plume movement inside a compartment. A counter-current flow model was developed to evaluate the buoyancy driven bidirectional exchange flow through the junctions. Also, a film tracking model was developed to simulate film flow on the contiguous walls. Special methods such as using variable time steps and non-uniform nodalization for heat sinks were applied to speed up the computation. Code assessments were carried out by simulating several separated effects tests (Phebus FPT0 test, JAERI tests) and integral effects tests (CVTR tests, NUPEC M-7-1 test). Comparing results between code simulations and experimental data showed that the code was capable of providing reasonable predictions.
While non-noble transition metal nanoparticles are widely explored in the field of solar energy harvesting and conversion at high temperatures, their high tendency to diffuse and oxidize may cause a substantially redu...
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While non-noble transition metal nanoparticles are widely explored in the field of solar energy harvesting and conversion at high temperatures, their high tendency to diffuse and oxidize may cause a substantially reduced lifetime of devices. To address this issue, herein, we demonstrate that Ni nanoparticles individually encapsulated in a densified ceramic shell, achieved by a SiO2 coating and a subsequent densification process, possess significantly enhanced stability at high temperatures. Ni diffusion is effectively prevented at temperatures as high as 800 degrees C, and the oxidation of the Ni nanoparticles is suppressed at 500 degrees C when exposed to air. A spectrally selective absorbing film fabricated with these densified Ni@SiO2 NPs exhibits high optical absorption with reflectance <20% in the main solar radiation region, superior to that of semiconductor Si-based solar absorbing films. It also exhibits high thermal stability at 500 degrees C in air, a temperature at which thermal degradation begins for most selective solar absorbers with high-melting-point metals and metal nitrides. The Ni@SiO2 absorbing film developed in this work outperforms state-of-the-art high-temperature solar absorbers, suggesting its applicability in high-temperature solar-thermal conversion systems.
The new energy electric vehicles can dramatically relief the environmental pollution problem caused by fuel automobiles. Based on the environmental and economic factors, this paper constructs an optimization model on ...
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The new energy electric vehicles can dramatically relief the environmental pollution problem caused by fuel automobiles. Based on the environmental and economic factors, this paper constructs an optimization model on the number of charging stations. Under the premise of minimizing the capacity of charging station, the optimal allocation of cities, suburbs and countryside is obtained. According to the site-selecting principles, South Korea is taken as a sample. Based on the station-building optimization model, when the conversion of electric-powered vehicle has fully realized, the number of stations should be 874524. In addition, based on the station-building cost optimization model, the number of stations in city area is 23796. In consideration of economic factors, Logistic model is built to evaluate the converting progress of South Korea, and the conclusion illustrates that it will take at least 8-17 years (from 10% to 100%). (C) 2019 The Authors. Published by Elsevier Ltd.
Experimental studies on the frictional pressure drop of air-water two-phase flows in vertical downward tubes are conducted in this paper. Experiments are performed at room temperature with the outlet pressure of exper...
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Experimental studies on the frictional pressure drop of air-water two-phase flows in vertical downward tubes are conducted in this paper. Experiments are performed at room temperature with the outlet pressure of experimental tube ranging from 0.17 MPa to 0.28 MPa, and four tubes are used with the tube inner diameter being 15 mm, 25 mm, 40 mm and 65 mm respectively. Based on the 978 data obtained in the experiments, prediction performances of 19 existing correlations, which have been developed for predicting the frictional pressure drop of gas-liquid two-phase flow in different tubes, are evaluated to assess the possibility and rationality of using these correlations to predict the frictional pressure drop of gas-liquid two-phase flow in vertical downward tubes as studied in the present paper. The results show that the prediction accuracy of the existing correlations for the frictional pressure drop of air-water two-phase flow in vertical downward tubes decreases remarkably with the increase in tube diameters, and the prediction values are far less than the experiment results under conditions with slug flow and churn flow patterns. It is also found that the buoyancy of bubbles can lead to the increase in the frictional pressure drop of the gas-liquid two-phase flow in vertical downward tubes, especially when big bubbles exist in the two-phase flow. A new model is then established in this paper by introducing a new parameter B into the separated flow model to consider the effect of buoyancy. It is found that in comparison with the existing correlations, the new model can well predict the frictional pressure drop of gas-liquid two-phase flows in vertical downward tubes with higher accuracy.
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