Gas self-ignition in a plane vortex chamber

This paper describes the numerical modeling of gas flow in a plane vortex chamber by using the Navier–Stokes equations. The model is based on the laws of conservation of mass, momentum, and energy for nonstationary two-dimensional compressible gas flow in the case of axial symmetry with a tangential component of the gas velocity. The processes of viscosity, thermal conductivity, and turbulence are accounted for. It is shown that the transition of the kinetic energy of gas into thermal energy as a result of transfer processes leads to the formation of hot spots in the boundary layers near the walls of the chamber. The gas temperature at these hot spots can exceed the gas combustion temperature, while the gas remains rather cold in the neighboring regions. This could be the reason for the cold gas self-ignition observed in the experiments. The turbulence of the flow and the processes of mixing and diffusion of the components make a significant contribution to the capacity of gas self-ignition.     

Experimental study of paddy drying in a vortex chamber

The intensification of interfacial mass, heat, and momentum transfer makes vortex chambers potentially interesting for the efficient drying of paddy, allowing shorter drying times and/or more compact equipment. The presence of a shell introduces particular challenges. Intraparticle diffusion limitations are strong and may reduce the advantage from intensified interfacial mass and heat transfer and the efficiency of air usage. Furthermore, high shear and normal stresses in the fast rotating particle bed may cause damage to the paddy shell, posing problems for transport and storage. With these specific aspects in mind, the use of vortex chambers for paddy drying is experimentally evaluated.     

旋流腔结构对涡流二极管性能及流动影响的数值模拟

为了探讨旋流腔结构对涡流二极管正向流动和反向流动的影响,分别采用RNG κ-ε湍流模型和κ-ε湍流模型进行了数值模拟,模拟结果与实验数据吻合良好。在此基础上,计算分析了旋流腔结构型式及几何尺寸对正向流动和反向流动的影响,并得到了旋流腔的优化结构。结果表明：渐缩型旋流腔反向阻力系数最大;薄板型正向阻力系数最小;渐缩型综合性能最佳,可以在原型基础上提高30%。渐缩型旋流腔中心高度应根据等流速设计原则,其最佳值略小于轴向出口管直径的1/4。     

Measurements of flow characteristics in a confined vortex flow

A study of air flow patterns by hot-wire anemometry is reported for a vortex chamber consisting of an upper cylindrical section 122 cm in diameter and 61 cm high and a conical bottom section 122 cm high. Quantitative data are presented for flow angles, profiles of mean tangential and axial velocities, and radial distributions of tangential and axial intensities of turbulence as a function of air entrance velocities of 1.6, 2.4 and 3.2 m/s, and axial distance from the top of the chamber. In general, the quantitative results confirm the theoretical predictions and the experimental trends reported in the literature. In particular, they fully support the conclusion that the flow pattern is relatively insensitive to the entrance volumetric flow rate. A generalized correlation is presented for the axial velocity distribution. Preliminary correlations are also presented for the tangential velocity distributions in the core and in the annular region of the vortex near the wall. These were found to be functions of the axial location and of the air entrance velocity.     

Calculation of a flow in prismatic tubes using the planar flow model

The turbulent flow of a Newton liquid in prismatic tubes was represented as a superposition of planar layers. The hydraulic resistance coefficient was calculated from the calculated rate profile in a planar layer. The only fitting parameter was the Reynolds number determined from the dynamic rate and the thickness of the viscous sublayer. The calculated data are in satisfactory agreement with the experimental data on the flow in tubes with a round, trigonal, square, and rectangular transverse section.     

Self-ignition of a two-component gas suspension

The self-ignition of a motionless cloud of particles of two sorts (the two-component gas suspension) is studied. We obtain approximate analytical expressions for the induction period and critical conditions of self-ignition in the case where the heat exchange occurs between the cloud and the ambient medium and in the case where one of the components consists of the particles of a substance that is reactive in the endothermic chemical reaction. These formulas are compared with the numerical solution of the unsteady problem, and their domains of applicability are found. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 6–13, September–October 1999.     

Characterization of Taylor vortex flow in a short liquid column

We present a study on Taylor vortex flow in the annulus between a rotating inner cylinder and a stationary outer cylinder, featured with a wide gap (radius ratio is 0.613) and a short column (aspect ratio is 5.17). A particle image velocimetry (PIV) system was used to determine the position, shape, and velocity distribution of the vortices, by which the flow was also confirmed to lie in the nonwavy Taylor vortex regime for all operating conditions explored in this study. Our results suggest that end boundary effects are important, in which the vortex number decreases with decreasing column length. For a system with an aspect ratio of 5.17, six vortices appear in the gap with their position, size, and shape varying at different Reynolds numbers. The fluid velocities show an asymmetric feature with respect to the vortex centers, while the maximum axial and radial velocities increase almost linearly with the increasing reduced Reynolds number (Re ? Re_c). In addition, computational fluid dynamics study was employed under the same conditions, and its results agree well with the PIV measurements. Overall, this study provides a quantitative understanding of the formation of Taylor vortices in a constrained space. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Hydrodynamic characteristics of a horizontal flow ejector in a rectangular chamber

The effects of the volumetric flow rate of primary motive water, water height, and the geometric parameters of the hydrodynamiccharacteristics of the gas suction rate and gas phase holdup were investigated in a rectangular chamber (0.22×0.26×1.2 m-high) with a horizontal flow ejector. Gas suction rate increased with increasing volumetric flow rate of the primary motive water, mixing tube length and diffuser length, but it decreased with increasing water height and nozzle diameter. The gas phase holdup was directly proportional to gas suction rate, indicating its corresponding increase with the volumetric flow rate of the primary motive water. Conversely, it decreased with increasing water height and nozzle diameter. However, the mixing tube length affected the gas phase holdup minimally compared to other operating parameters. Both the gas suction rate and gas phase holdup correlated with the dimensionless equations of operating parameters.     

基于波理论的涡街流量计雾状流测量模型

建立了雾状流条件下涡街流量计的修正模型。雾状流中液相的存在会导致涡街流量计的测量误差,通过将以往研究者在单相流中对Karman涡街现象的认识及取得的研究成果作为基础,并结合实验流体本身所具有的动力特点,利用Karman涡街波传递的理论分析了非定常不稳定的雾状流流场中的Karman涡街现象,构建了双向耦合的气液两相流动力学模型。试验结果显示,当液相体积含率从0～0.13%变化时,模型修正后的结果与实际值较为接近。     

涡街流量计在化工行业流量测量中的应用

结合化工行业流量仪表应用的实践,介绍了涡街流量计的测量原理,涡街流量计的选择和安装。提出了在化工行业的流量测量中使用涡街流量计的注意事项。     

A heat transfer relation for swirl flow in a vortex tube

An experimental investigation was made to study the heat transfer behavior of a water-cooled vortex tube with air as the working medium. The vortex flow was generated by leading the compressed air to enter the vortex tube tangentially. The pressures of the inlet air were 300 to 500 kPa gauge. For each of these inlet pressures, the heat transfer performance of the vortex tube was studied at different cold mass flow ratios. New experimental data are presented. An empirical correlation for the prediction of the air-side Nusselt number is established. It was shown that the air-side Nusselt number for the swirl flow in this vortex tube can be up to 30 times higher than that for a flow without swirl in the same tube.     

Explosion-free flash drying of coal in a vortex flow of heat-transfer gas

The process of rapid nonexplosive drying of coals in cyclone-type devices has been considered. The principles of calculation of a vortex chamber, the characteristics of thermally treated coal, and the main promising lines in the vortex drying of coals are discussed.     

Multiphase flow at the edge of a steam chamber

The use of steam‐assisted gravity drainage (SAGD) to recover bitumen from Athabasca deposits in Alberta has been growing. Butler [Butler, J. Can. Pet. Tech. 1985;24:42–51] derived a simple theory to calculate the production rate of oil during SAGD in an ideal reservoir. This simple and useful theory made several assumptions about the properties of the reservoir and operating conditions of the process. The theory also assumed that the highest mobility oil is at the edge of the steam chamber and that the oil phase velocity is highest at the chamber edge and reduces with distance into the oil sand. This research examines flow conditions at the edge of the steam chamber. Specifically, a new theory is derived that takes into account the impact of oil saturation and relative permeability on the oil mobility profile at the edge of a steam chamber. It is shown that the flow behaviour at the edge of a steam chamber is more complex and is not fully represented by Butler's theory. Contrary to Butler's theory, the oil mobility has its maximum some distance away from the edge of the steam chamber. The results reveal that the higher the thermal diffusivity of the oil sand, the deeper the location where the oil phase velocity is maximum. The developed model has been validated against published experimental and field data.     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the later.     

Taylor vortex flow in presence of internal baffles

We present a study on Taylor vortex flow in between a rotating inner cylinder and a stationary outer cylinder with vertical or horizontal baffles. A mineral oil is used as the working fluid in the annular channel of 60 mm in height and 11.6 mm in gap width. The flow pattern in the annulus is investigated by particle image velocimetry (PIV) and computational fluid dynamics (CFD). Both the experimental and simulation results show that the presence of vertical baffles influences the vertical positions of vortices—it is primarily significant for the bottom vortex. Increasing number of vertical baffles gradually decreases the azimuthal variation in the vertical position. The baffles also lead to the occurrence of a circulation flow immediately upstream and downstream each baffle plate in the radial–azimuthal plane. On the other hand, an annular horizontal baffle with sufficient width alters the vortex structure in the gap, for instance, fewer vortices are observed. With two horizontal baffles in the annulus, the flow pattern is largely affected by the baffle width and the distance between the two baffles. This study provides a better understanding of Taylor vortex in presence of internal baffles, which will be important for practical applications of Taylor vortex devices.     

Retention capacities and flow patterns of vortex contactors

The hydrodynamic features of vortex contactors, such as vortex chambers and contactors with swirled spouted beds, designed for the thermal treatment of dispersed materials, such as drying, when the material comes into direct contact with the swirling flow of the heat carrier gas are considered. The retention capacity of vortex chambers with vertical and horizontal axes is calculated and the flow patterns in vortex contactors are analyzed.     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the latter.