不同形式大棚内部气流流态的比较

运用三维不可压缩流体的RNGk-ε紊流模型,分别对拱型、屋脊型和斜顶型大棚内部气流场进行精细的数值模拟。结果表明:3种大棚在进气口附近都存在着多个回流区,流动呈现高度的三维特性,流态较为复杂,而在远离进口的大部分区域,流动趋于均匀。大棚进口两侧的回流区范围较大,其具体范围因大棚形式的不同而有明显的变化,大棚形式对其内部气流流态有显著的影响。

大棚结构型式比较分析

运用三维不可压缩流体的紊流模型,分别对拱型、屋脊型和斜顶型大棚内部气流场进行了精细的数值模拟,并在此基础上进一步计算了大棚的1次换气时间。从模拟结果可以看出,不同型式的大棚,其内部回流区的范围和流速分布形态明显不同,大棚的型式对其内部气流流态有显著的影响。在大棚尺寸和进出口条件相同的情况下,斜顶型大棚换气时间最短,拱型大棚次之,屋脊型大棚换气时间最长。从大棚内部气流流态好坏和1次换气时间长短角度看,斜顶型大棚结构型式较佳。

Flow Pattern and Pressure Fluctuation of Severe Slugging in Pipeline-riser System

During the exploitation of offshore oil and gas,it is easy to form severe slugging which can cause great harm in the riser connecting wellheads and offshore platform preprocessing system.The flow pattern and pressure fluctuation of severe slugging were studied in an experimental simulation system with inner diameter of 0.051 m.It is found that severe slugging can be divided into three severe slugging regimes：regime I at low gas and liquid flow rates with large pressure fluctuation,intermittent flow of liquid and gas in the riser,and apparent cutoff of liquid phase,regime II at high gas flow rate with non-periodic fluctuation and discontinuous liquid outflow and no gas cutoff,regime III at high liquid flow rate with degenerative pressure fluctuation in form of relatively stable bubbly or plug flow.The results indicate that severe slugging still occurs when the declination angle of pipeline is 0,and there are mainly two kinds of regimes：regime I and regime II.As the angle increases,the formation ranges of regime I and regime III increase slightly while that of regime II is not affected.With the increase of gas superficial velocity and liquid superficial velocity,the pressure fluctuation at the bottom of riser increases initially and then decreases.The maximum value of pressure fluctuation occurs at the transition boundary of regimes I and II.

Characteristics of fluidization and dry-beneficiation of a wide-size-range medium-solids fluidized bed

Wide-size-range medium-solids are used in a modularized coal beneficiation demonstration system with a gas-solid fluidized bed. The characteristics of fluidization and dry-beneficiation of the medium solids were studied. The numerical simulation results show that 0.15–0.06 mm fine magnetite powder can decrease the disturbances caused by the bubbles. This is beneficial to the uniformity of the gas-solid interactions and thus to the uniformity and stability of the bed density and height. The experimental results show that, with an increase in the fine coal content in medium solids, both the fluidization quality and the beneficiation performance of the bed decreased gradually. When the fine coal content was no more than 13%, a relatively high superficial gas velocity increased the beneficiation efficiency. When the content was more than 13%, part of the fine coal was separated, leading to product layers. The separation efficiency was therefore gradually decreased. The models for predicting the bed density standard deviation and the probable error, E, value were both proposed. The E value can reach to 0.04–0.07 g/cm^3 under the optimized experimental parameters. This work provides a foundation for the adjustment of the bed density and the separation performance of the modularized 40–60 ton per hour dry coalbeneficiation industrial system.

Wavelet Characterization of the Flow Regime in a Gas-Solid Fluidized Bed

Processes like combustion, pyrolysis or gasification of coal and biomass are typical applications of gas-solid fluidized beds. These reactors normally use silica sand as the inert material inside the bed and the sand particles represent around 95% of the total bed weight. Pressure measurements have been used to characterize the dynamic behavior of fluidized beds since early researches in the area. Pressure fluctuations are generally due to bubbles flow which characterizes the fluidization regime. The present work aims to perform a time-frequency analysis of the pressure signal acquired in an experimental apparatus on different gas-solid flow regimes. Continuous and discrete wavelet transforms were applied and the results were compared with image records acquired simultaneously with the pressure signal. The main frequencies observed are in accordance with the ones obtained through Fourier spectra. The time-frequency distribution of the signal agrees with the phenomena observed in the image record, remarkably for the slugging flow. Some additional research is still necessary to completely characterize the flow regimes using the wavelet scalograms but the present results show that the task is a very promising one.

Cavity flow regime for spillway aerators

It is well known that the effect of air entrainment for cavitation damage controls is related not only to the air discharge into aerator devices but also the flow regime of the cavity below them.On the basis of the hydraulic characteristics of the flow,the aerator devices were for the first time classified.The theoretical considerations were performed about the jet length and cavity flow regime with the influencing factors.Comparing with the behavior of the flow through the aerator of discharge tunnels,the flow regimes of the cavity below spillway aerators were experimentally investigated,and the empirical expressions were presented to identify the conversions of the cavity flow regimes,including fully filled cavity,partially filled cavity,and net air cavity.Some issues of the design of the aerator devices were suggested in the present work.

Nodal Topological Phases in s-wave Superfluid of Ultracold Fermionic Gases

The gapless Weyl superfluid has been widely studied in the three-dimensional ultracold fermionic superfluid. In contrast to Weyl superfluid, there exists another kind of gapless superfluid with topologically protected nodal lines, which can be regarded as the superttuid counterpart of nodal line semimetal in the condensed matter physics, just as Weyl superfluid with Weyl semimetal. In this paper we study the ground states of the cold fermionic gases in cubic optical lattices with one-dimensional spin-orbit coupling and transverse Zeeman field and map out the topological phase diagram of the system. We demonstrate that in addition to a fully gapped topologically trivial phase, some different nodal line superfluid phases appear when the Zeeman field is adjusted. The presence of topologically stable nodal lines implies the dispersionless zero-energy fiat band in a finite region of the surface Brillouin zone. Experimentally these nodal line superfluid states can be detected via the momentum-resolved radio-frequency spectroscopy. The nodal line topological superfluid provide fertile grounds for exploring exotic quantum matters in the context of ultraeold atoms.