STUDY OF AXIAL VELOCITY IN GAS CYCLONES BY 2D-PIV,3D-PIV,AND SIMULATION

The axial velocity distribution in a gas cyclone has been examined with two-dimensional particle image velocimetry （2D-PIV） and three-dimensional particle image velocimetry （3D-PIV） experiments in this study. Due to the limitation of 2D-PIV configuration, the contamination generated by the strong tangential velocity in the cyclone can be registered in the axial velocity detected by 2D-PIV. Efficient methods are proposed in this work to remove this contamination. The contamination-removed 2D-PIV data agree well with 3D-PIV results. The distributions of the axial velocity are also computed by the Reynolds stress model （RSM） and verified using the PIV experimental results. Reasonable agreements are obtained.

BEHAVIOR OF OBSTRUCTED SQUARE BUOYANT VERTICAL JETS IN STATIC AMBIENT (Ⅱ)-ANALYSIS ON BEHAVIOR OF FLOW FIELD

Based on a series of numerical calculations, the behavior of flow field in obstructed square buoyant vertical jet is summarized and analyzed. Based on the axial line velocity distribution, the flow after the disc can be divided into three regions, i.e., recirculation region, transitional region and self-similar region The characteristic of selfsimilarity of upright velocity was validated. The three regions can also be distinguished based on the axial velocity. The axial velocity in self-similar region was found to obey the same law and the formula presented by introducing the velocity expression used by Chen and Rodi. The isolines of pressure on cross-sections of different heights were displayed and the production, expansion, breaking and disappearing of negative pressure regions were found.

Forming and breaking the ceiling of inlet gas velocity regarding to separation efficiency of cyclone

The maximum-efficiency inlet velocity(MEIV)is a ceiling of inlet gas velocity that defines separation efficiency during cyclone design and operation.Experiment and computational fluid dynamics(CFD)simulation exhibited that an apex cone at the dust outlet can break the ceiling and improve the sepa-ration efficiency.The phenomenon is closely related to the effect of excessive high inlet gas velocity on the back-mixing escape of fine particles,which is the final result of back mixing,entrainment by the rapid upward airflow,and secondary separation of the inner vortex.In the center of the inner vortex,the airflow rotates slowly and moves rapidly upward.This elevator type of airflow delivers re-entrained particles to the vortex finder.A higher inlet gas velocity accelerates the elevator,causing more entrained particles to escape.This explains the decrease in efficiency at an excessively high inlet gas velocity.When an apex cone is installed at the dust outlet,the back-mixing is significantly weakened because the vortex core is bounded to the center of separator,while the transport effect of rapid upward airflow is weakened by the decrease in axial velocity in the center.Therefore,particle escape is weakened even at excessive high inlet gas velocities.Instead,the centrifugal effect is enhanced because of increased tangential velocity of the gas and particles.Consequently,the ceiling of inlet gas velocity is broken.

Axial laminar velocity field calculation and optimization for power-law fluid in eccentric annulus with cutting bed

The formation of a cutting bed in an annulus involves safety problems in drilling especially in the horizontal well and the directional well. In this work, three axial laminar velocity field calculation models for the power-law fluid in an annulus are modified by considering the effect of the cutting bed. The proposed models are employed to numerically simulate the annulus flow with the cutting bed. Verified by the experimental data in literature, all of them can be applied to the situation of the annulus flow with the cutting bed. The modified concentric annulus model enjoys the best performance, while the flat channel flow model has the worst performance.

VELOCITY PROFILES FOR AXIAL LAMINAR FLOW OF POWER-LAWFLUIDS THROUGH ECCENTRIC ANNULI

An analytical solution of velocity profiles for Non-Newtonian fluids described by the power-law equation in axial laminar flow through eccentric annuli is presented.The expressions of limit velocities and contours of equal velocity are obtained. The main approaches,claimed in this paper,are that the term T_(rz)/r in the differential equation of flow and the non-symmetrical velocity distribution about the geometric center of the radial clearance are considered.

Experimental study of flow field in interference area between impeller and guide vane of axial flow pump

Axial flow pump is a kind of typical pumps with rotor-stator interaction, thus the measurement of the flow field between impeller and guide vane would facilitate the study of the internal rotor-stator interaction mechanism. Through a structural modification of a traditional axial flow pump, the requirements of particle image velocimetry（PIV） measurement are met. Under the condition of opt.0.8Q, the axial vortex is identified between impeller hub and guide vane hub, which is developed into the main flow and to affect the movement when the relative positions of impeller and guide vane at different flow rates are the same. Besides, the development and the dissipation of the tip leakage and the passage vortex in impeller passages are mainly responsible for the difference of the flow field close to the outer rim. As the flow rate decreases, the distribution of the meridional velocities at the impeller outlet becomes more non-uniform and the radial velocity component keeps increasing. The PIV measurement results under the condition of opt.1.0Q indicate that the flow separation and the trailing vortex at the trailing edge of a blade are likely to result in a velocity sudden change in this area, which would dramatically destroy the continuity of the flow field. Moreover, the radial direction of the flow between impeller and guide vane on the measurement plane does not always point from hub to rim. For a certain position, the direction is just from rim to hub, as is affected by the location of the intersection line of the shooting section and the impeller blade on the impeller as well as the angle between the intersection line and the rotating shaft.

Simulation of Combustion Flow of Methane Gas in a Premixed Low-Swirl Burner using a Partially Premixed Combustion Model

Because the rotational current stabilizes the flame by creating a recirculation zone,it may increase the risk of reversal.For this reason,low-spin combustion is used to stabilize the flame while preventing flashbacks.Therefore,in this study,the combustion flow of methane gas in a low-swirl burner is simulated using a partially premixed combustion model.Furthermore,the fuel flow rate is considered constant.The research parameters include swirl angle(θ=35°–47°),equivalence ratio(φ=0.6–0.9)and inlet axial flow radius(R=0.6–0.7)and effect of these parameters on temperature distribution,flame length,flame rise length,velocity field,and streamlines of the number of pollutant species are investigated.The contours of streamline,temperature distribution,and velocity distribution are also presented for analysis of flow physics.The results show that with increasing the fuel-air ratio,the strength of the axial flow decreases,and the position of the maximum flame temperature shifts toward the inlet of the reactants.The results also reveal that by increasing the swirl angle of the flow,the position of the minimum velocity value(opposite to the direction of the axis)tends towards the outlet.The results also indicate that the maximum temperature of the combustion chamber increases with increasing the swirl angle,and inθ=35°,the maximum temperature is 1711℃and inθ=41°,this value is 1812℃.Finally,by increasing the swirl angle toθ=47°,the maximum flame temperature position is found at a considerable distance from the inlet and is 1842℃.

Effects of the support material addition on the hydrodynamic behavior of an anaerobic expanded granular sludge bed reactor

As a support material, zeolite can be used to promote the granulation process due to its high settable property and the ability to retain biomass on its surface. The present paper reports on the influence of zeolite addition on the hydrodynamic behavior of an expanded granular sludge bed reactor（EGSB）. Different models were applied to fit the flow pattern and to compare EGSB hydrodynamic performance with and without the addition of zeolite. The experimental data fit the tanks in a series model for zeolite bed height of 5 cm and upflow velocity of 6 m/hr.Higher axial dispersion degree（D/uL） was obtained at lower heights of zeolite. The real hydraulic retention time（HRTr） was increased with both increased zeolite bed height and increased upflow velocity. The short-circuit results for 5 cm of zeolite bed and 6, 8 and 10 m/hr upflow velocity were 0.3, 0.24 and 0.19 respectively, demonstrating the feasibility of using zeolite for a proper hydrodynamic environment to operate the EGSB reactor. The presence of zeolite resulted in the higher percentage values of dead zones, ranging from 12% to 24%.Zeolite addition exerted a positive effect on the hydrodynamics pattern for this technology being advantageous for the anaerobic process because of its possible contribution to better biofilm agglomeration, granule formation and substrate-microorganism contact.