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751.
752.
The effect of solid-phase wall boundary condition on the numerical simulation of gas-solid flow in CFB risers containing FCC particles was investigated using the two-fluid model incorporating the kinetic theory of granular flow.Both the Gidaspow drag model and the EMMS-based drag model were used.The Johnson and Jackson(1987) wall boundary condition was applied to describe the interaction between particles and wall.Based on the experimental system of Li and Kwauk(1994),parametric studies of specularity coefficient(φ=1.0,0.6,0.0005,0.00005,0) and particle-wall restitution coefficient(e_w=0.6,0.9,0.95,0.99,0.999) were performed to evaluate their effects on axial voidage profile,solids flux,meso-scale and heterogeneous structures.Simulation results showed that solid-phase wall boundary condition had little effect on axial voidage profile when the Gidaspow drag model was used.However,the specularity coefficient φ had a pronounced influence on flow behavior when the EMMS-based drag model was used,and a small specularity coefficient(φ=0.00005,0) could result in better agreement with experimental data.The particle-wall restitution coefficient e_w plays but a minor role in the holistic flow characteristics. 相似文献
753.
双模态发动机的模态鉴别方法 总被引:1,自引:0,他引:1
双模态冲压发动机的不同燃烧模态具有不同的稳焰机制和流态特征,并且在模态转换时伴随着显著的推力变化. 因此,准确判断燃烧模态,对于捕捉发动机的燃烧区位置/范围、释热分布特征,以及为进一步优化燃烧室的设计(流道结构和供油布局) 具有重要意义. 目前尚无鉴别模态的有效试验方法,本文提出了一种模态鉴别的试验方法,并在超燃直连台上开展验证试验. 试验中使用的测量技术包括:壁面静压、高速阴影/纹影、多通道可调谐二极管吸收光谱和高能态碳氢自由基CH* 自发光成像. 利用多种测量方法的组合,可以同时获得燃烧室中气流静温、速度、马赫数分布,释热分布以及燃烧区位置/范围. 这些试验数据能够用于判别模态,并获得不同模态的流动和火焰特征. 相似文献
754.
诸多隧道围岩由宽级配的砾石土组成,砾石土含水率和粗料含量变化时,其力学性能存在较大差异。本文选取集呼高速金盆湾隧道浅埋段具有代表性的砾石土样本进行了室内大型直剪试验,研究了砾石土的力学性能随含水率和粗料含量的变化规律。试验结果表明:当含水率在5.37%~19.19%之间变化时,粘聚力随粗料含量的变化呈相同的变化规律,随着粗料含量增加,粘聚力先迅速下降,后显著增高,在粗料含量为45%左右时取得最小值;当含水率为10%~15%之间的某值时,细料颗粒处于最优含水率状态,当含水率超过最优含水率时,粘聚力显著下降;内摩擦角随粗料含量增加逐渐增加,随含水率增加逐渐降低;结合隧道围岩砾石土的颗粒级配特征,当含水率大于10%时,粘聚力和内摩擦角显著降低,隧道围岩稳定性也随之降低。 相似文献
755.
Numerical Simulations of Unsteady Flows from Rarefied Transition to Continuum Using Gas-Kinetic Unified Algorithm 下载免费PDF全文
Junlin Wu Zhihui Li Aoping Peng & Xinyu Jiang 《advances in applied mathematics and mechanics.》2015,7(5):569-596
Numerical simulations of unsteady gas flows are studied on the basis of
Gas-Kinetic Unified Algorithm (GKUA) from rarefied transition to continuum flow
regimes. Several typical examples are adopted. An unsteady flow solver is developed
by solving the Boltzmann model equations, including the Shakhov model and
the Rykov model etc. The Rykov kinetic equation involving the effect of rotational
energy can be transformed into two kinetic governing equations with inelastic and
elastic collisions by integrating the molecular velocity distribution function with the
weight factor on the energy of rotational motion. Then, the reduced velocity distribution
functions are devised to further simplify the governing equation for one- and two-dimensional
flows. The simultaneous equations are numerically solved by the discrete
velocity ordinate (DVO) method in velocity space and the finite-difference schemes in
physical space. The time-explicit operator-splitting scheme is constructed, and numerical
stability conditions to ascertain the time step are discussed. As the application
of the newly developed GKUA, several unsteady varying processes of one- and two-dimensional
flows with different Knudsen number are simulated, and the unsteady
transport phenomena and rarefied effects are revealed and analyzed. It is validated
that the GKUA solver is competent for simulations of unsteady gas dynamics covering
various flow regimes. 相似文献
756.
Xinyu Sun Xueyan Feng Xiao-Yun Yan Jiancheng Luo Ruimeng Zhang Tao Li Hui Li Jiahui Chen Fangbei Liu Ehsan Raee Stephen Z. D. Cheng Tianbo Liu 《Chemical science》2021,12(36):12130
We report herein that dendron-shaped macromolecules ABn crystallize into well-ordered pyramid-like structures from mixed solvents, instead of spherical motifs with curved structures, as found in the bulk. The design of the asymmetric molecular architecture and the choice of mixed solvents are applied as strategies to manipulate the crystallization process. In mixed solvents, the solvent selection for the Janus macromolecule and the existence of dominant crystalline clusters contribute to the formation of flat nanosheets. Whereas during solvent evaporation, the bulkiness of the asymmetric macromolecules easily creates defects within 2D nanosheets which lead to their spiral growth through screw dislocation. The size of the nanosheets and the growth into 2D nanosheets or 3D pyramidal structures can be regulated by the solvent ratio and solvent compositions. Moreover, macromolecules of higher asymmetry generate polycrystals of lower orderliness, probably due to higher localized stress.The dendron-shaped macromolecules ABn crystallize into well-ordered pyramid-like structures from mixed solvents, which is on the contrary to spherical motifs with curved structures in bulk. 相似文献
757.
Synthesis of polyaniline nanofibers by "nanofiber seeding" 总被引:15,自引:0,他引:15
Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers (usually <1%) dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nanofibers. The nanoscale morphology of the original seed template is transcribed almost quantitatively to the bulk precipitate. These findings could have immediate impact in the design and development of high-surface area electronic materials. 相似文献
758.
Duanming Zhang Zhihua Li Xinyu Tan Ranran Fang Gaobin Liu 《Applied Surface Science》2007,253(14):6144-6148
The vaporization effect and the following plasma shielding generated by high-power nanosecond pulsed laser ablation are studied in detail based on the heat flux equation. As an example of Si target, we obtain the time evolution of the calculated surface temperature, ablation rate and ablation depth by solving the heat flow equations using a finite difference method. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the variation of ablation depth per pulse with laser fluence is performed. Our numerical results are more agreed with the experiment datum than other simulated results. The result shows that the plasma shielding is very important. 相似文献
759.
Zhaohang Zuo Shuting Liu Weiqiao Pang Baoxin Lu Wei Sun Naidan Zhang Xinyu Zhou Dongjie Zhang Ying Wang 《Molecules (Basel, Switzerland)》2022,27(9)
Accumulating attention has been focused on resistant starch (RS) due to its blood-lipid-lowering activities. However, reports on the potential bioactivities of RS for preventing hyperlipidemia acute pancreatitis (HLAP) are limited. Therefore, in this study, an acute pancreatitis model was set up by feeding a hyperlipidemia diet to rats, and subsequently evaluating the anti-HLAP effect of RS in kidney beans. The results show that the IL-6, IL-1β, and TNF-α of serum in each RS group were decreased by 18.67–50.00%, 7.92–22.89%, and 8.06–34.04%, respectively, compared with the model group (MOD). In addition, the mRNA expression of tight junction protein ZO-1, occludin, and antibacterial peptides CRAMP and DEFB1 of rats in each RS group increased by 26.43–60.07%, 229.98–279.90%, 75.80–111.20%, and 77.86–109.07%, respectively. The height of the villi in the small intestine and the thickness of the muscle layer of rats were also increased, while the depth of the crypt decreased. The present study indicates that RS relieves intestinal inflammation, inhibits oxidative stress, and prevents related intestinal barrier damage. These results support the supplementation of RS as an effective nutritional intervention for HLAP and associated intestinal injury. 相似文献
760.
The redox reaction is a normal process of biological metabolism in the body that leads to the production of free radicals. Under conditions such as pathogenic infection, stress, and drug exposure, free radicals can exceed normal levels, causing protein denaturation, DNA damage, and the oxidation of the cell membrane, which, in turn, causes inflammation. Acanthopanax senticosus (A. senticosus) flavonoids are the main bioactive ingredients with antioxidant function. H2O2-treated RAW 264.7 cells and DSS-induced colitis in mice were used to evaluate the antioxidant properties of A. senticosus flavonoids. The results show that A. senticosus flavonoids can significantly downregulate the levels of ROS and MDA in H2O2-treated RAW 264.7 cells and increase the levels of CAT, SOD, and GPx. A. senticosus flavonoids can also increase the body weights of DSS-induced colitis mice, increase the DAI index, and ameliorate the shortening of the colon. ELISA experiments confirmed that A. senticosus flavonoids could reduce the level of MDA in the mouse serum and increase the levels of SOD, CAT, and GPx. Histopathology showed that the tissue pathological changes in the A. senticosus flavonoid group were significantly lower than those in the DSS group. The Western blot experiments showed that the antioxidant capacity of A. senticosus flavonoids was accomplished through the Nrf2 pathway. In conclusion, A. senticosus flavonoids can relieve oxidative stress in vivo and in vitro and protect cells or tissues from oxidative damage. 相似文献