Identification and prediction of air core diameter in a hydrocyclone by a novel online sensor based on digital signal processing technique

A hydrocyclone is a particle separation device widely used in chemical and allied process industries in which a particle-fluid mixture is injected tangentially creating a strong swirling, recirculation flow. The particle separation efficiency increases by suppressing the air core, so online prediction of air core formation has significant importance in the industrial operations. Performance of hydrocyclone is greatly influenced by shape and size of air core. A novel type of senor technique has been developed to identify and predict the air core diameter from online live data using data acquisition card. The true signal amplitudes change as a function of the time was used with noise interruption for random changes in amplitude. Noises are eliminated by using moving average technique. The slope of the curve is continuously tracked to determine sudden or abrupt change and indicates the formation of air core. It has been observed that a strong air core of diameter 0.95 cm to 1.2 cm was formed during experimentation and matched with predicted values over an entire flow regime. The experimental and finally an alarm is designed which gives alerts once air core is formed and calculates air core diameter. For calculating air core diameter a polynomial equation is fitted between pressure difference and the pressure transmitter reading. A simple moving average with a smooth width of 10 was used for prediction of air core. Experimental results indicate that the digital signal sensor techniques identify the air core and measure air core diameter very accurately and can be used in many mining and mineral based chemical and allied process industries.     

内翅片管中堵塞芯管直径优化的数值模拟

采用可实现的k-ε湍流模型和壁面函数法对带不同直径堵塞芯管的内翅片管内空气的湍流流动和换热特性进行了数值模拟,利用试验数据检验了计算方法的正确性。在对不同流量下改变芯管直径进行数值模拟的结果表明：在一定流量下,芯管外径与外管内径之比存在着一个最佳值,使单位压降、单位翅片面积下的换热量最大,而且随着流量的增加,最佳芯管外径与外管内径之比呈减小趋势。在本文所研究的参数范围内,这一最佳比值在0.5-0.625之间。同时也对在相同压降条件下进行了数值计算,结果表明,当芯管外径与外管内径最佳比值为0.4-0.56左右时,单位翅片面积下的流量和换热量之积达最大值。这一结论为内翅片管的优化设计提供了重要依据。     

Effect of Clean Air Core Geometry on Fine Particle Contamination And Calibration of a Virtual Impactor

ABSTRACT

The optimum diameter and position of the clean air core in a clean air core virtual impactor were experimentally determined. It was found that the clean air core diameter should be at least twice as large as the converging nozzle diameter and that the clean air core should be positioned so that the ratio of the clean air flow velocity to the aerosol flow velocity ranges from 1.5 to 5.0 at the outlet of the clean air tube. Use of a laminator in a virtual impactor was found to increase the particle loss while maintaining almost the same collection efficiency curve.     

Drying performance of a tumbler dryer with condenser

The effects of flow rates of hot air and cooling water on drying percentage and energy efficiency of cotton lint in a cylindrical type drum tumbler dryer (0.54m-ID×0.34m-high) have been determined. Drying of the lint is mainly affected by flow rate of hot air, which is a function of the diameter ratio (D_M/D_F) of motor and fan pulley and motor capacity. During the drying process in the tumbler dryer, temperatures and humidity before and after were measured to determine the drying characteristics. The volumetric flow rate of hot air increases with increasing the diameter ratio of the motor and fan pulley, whereas the volumetric flow rate of hot air decreases with an increase in the mass flow rate of the cooling water through the condenser. The energy consumed by the motor relied more on the diameter ratio of the motor and fan pulley as opposed to the mass flow rate of cooling water. Despite the increase in the drying percentage with increasing the diameter ratio of the motor and fan pulley and the mass flow rate of the cooling water, the energy efficiency decreased.     

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.     

The efficiency of short airlift pumps operating at low submergence ratios

An airlift pump operating at submergence ratios between 0.2 and 0.6 and using water as the pumping liquid, has been investigated. Circular pipes of constant short length of 1 m and inner diameters of 3 and 5 cm were used as riser tubes. The water flow rate measurements for various air flow rates allowed the study of the pumping efficiency as a function of the air flow rate, submergence ratio and certain geometrical parameters (riser tube diameter and injector design). The efficiency curves start from a zero efficiency at a minimum air flow rate, then increase rapidly with the air flow rate up to an efficiency maximum. For higher air flow rates, the efficiency decreases exponentially. Diagrams showing the influence of the riser tube diameter and injector design, are presented. Additionally, based on the experimental data, two equations are presented, which allow the prediction of the maximum efficiency and the corresponding water and air flow rates inside the experimental range.     

The velocity distribution within a hydrocyclone operating without an air core

The three dimensional flow patterns in a 3-in. diameter hydrocyclone operating without an air cone were studied using tracer particles and cine photography. Analysis of films at 55 locations inside the hydrocyclone yielded data for 18 velocity profiles at six vertical positions. These data were checked for consistency and compared with the results of earlier work in hydrocyclones operating with air cores. The tangential velocity profiles were found to be similar to those produced with an air core although, n. in V_AIⁿ = const, is about 0.2 to 0.4 instead of 0.7 to 0.8 for air core operation. In this work the radial velocity component was relatively independent of radius.     

Study of Air‐Liquid Flow Patterns in Hydrocyclone Enhanced by Air Bubbles

In order to improve the oil‐water separation efficiency of a hydrocyclone, a new process utilizing air bubbles has been developed to enhance separation performance. Using the two‐component phase Doppler particle analyzer (PDPA) technique, the velocities of two phases, air and liquid, and air bubble diameter were measured in a hydrocyclone. The air‐liquid mixing pump can produce 15 to 60 μm‐diameter air bubbles in water. There is an optimum air‐liquid ratio for oil‐water separation of a hydrocyclone enhanced by air bubbles. An air core occurs in the hydrocyclone when the air‐liquid ratio is more than 1 %. The velocities of air bubbles have a similar flow pattern to the water phase. The axial and tangential velocity differences of the air bubbles at different air‐liquid ratio are greater near the wall and near the core of the hydrocyclone. The measured results show that the size distribution of the air bubbles produced by the air‐liquid mixing pump is beneficial to the process where air bubbles capture oil droplets in the hydrocyclone. These studies are helpful to understand the separation mechanism of a hydrocyclone enhanced by air bubbles.     

Flow field in the freeboard of vortexing fluidized bed

A systematic investigation on the flow field in a vortexing fluidized bed cold model was reported. The gas velocity profiles within the freeboard with diameters of 0.19 m and 0.29 m were measured by using a five-hole pitot tube. A new parameter, called vortex number, V_or defined as the ratio of tangential velocity to axial velocity of the swirling gas stream, was proposed for representing the swirl intensity. V_or is found to be increased with secondary air velocity, and decreased with primary air velocity and diameter of secondary air nozzles. It is also found that the profile of swirl flow is significantly affected by the arrangement of the secondary air nozzles. The effects of inserted length of secondary air nozzles and geometric structure of expansion section on the swirl flow are also studied. Based on the experimental data, a correlation is presented to estimate the vortex number. Vortex number is found to be a function of the geometric structure of exhaust tube, diameter of secondary air nozzle and tangential air flow rate.     

Hydrodynamic aspects of ejectors

The use of ejectors as a gas-liquid contacting device has been reported to give higher mass transfer rates than conventional contactors. Computational fluid dynamics (CFD) modeling studies were undertaken to understand the hydrodynamic characteristics with reference to the ejector geometry. The CFD model also provides a basis for quantifying the effects of operating conditions on the ejector performance. CFD studies show that at low value of area ratio (ratio of throat area to nozzle area), due to the larger diameter of the water jet, the annular area available for air flow reduces, causing recirculation of the entrained air within the converging section of the ejector. On the other hand, for higher values of area ratio, due to smaller diameter of the water jet, the momentum transfer to the air decreases and all the entrained air cannot be forced through the throat. As a result, the net air flow rate going into the throat for both area ratios is small. Thus there is an optimum area ratio for the maximum air entrainment rate. The air entrainment rate correlates with pressure difference between the air entry and throat exit for a wide variety of ejector geometries and operating conditions. The overall head loss factor and the ejector efficiency can be predicted a priori.     

EFFECTS OF GRADIENT MAGNETIC FIELDS ON THE MAGNETO-THERMAL MIXED CONVECTION OF AIR IN A HORIZONTAL PIPE

Effects of gradient magnetic fields on the mixed convection of air in a gravity field are numerically studied with 3-D model equations. The detailed characteristics of the magneto-thermal wind in a pipe are computed for the length ratios L (pipe length divided by pipe diameter) of 20, 30, 62, and 100, with diameter ratios N (diameter of an electric coil versus that of the pipe) from 2 to 200. It is found that there exists a best diameter ratio N to maximize the airflow rate for a channel with a fixed length. Detailed flow and temperature profiles are graphically presented for various values of N.     

EFFECTS OF GRADIENT MAGNETIC FIELDS ON THE MAGNETO-THERMAL MIXED CONVECTION OF AIR IN A HORIZONTAL PIPE

Effects of gradient magnetic fields on the mixed convection of air in a gravity field are numerically studied with 3-D model equations. The detailed characteristics of the magneto-thermal wind in a pipe are computed for the length ratios L (pipe length divided by pipe diameter) of 20, 30, 62, and 100, with diameter ratios N (diameter of an electric coil versus that of the pipe) from 2 to 200. It is found that there exists a best diameter ratio N to maximize the airflow rate for a channel with a fixed length. Detailed flow and temperature profiles are graphically presented for various values of N.     

水平管内多孔板后的气液两相流型可视化实验

多孔板后是否形成均匀分散的泡状流流型是影响多孔板废气吸收装置吸收效果的关键因素。以空气和水作为两相介质,对气液两相混合物在水平管内流经多孔板后形成的流型进行实验。通过孔径分别为2、3、4、5 mm的4只多孔板在内径98.5 mm水平有机玻璃管内的可视化流动及高速摄像,研究了孔径大小、气相流量变化及液相流量变化对多孔板后流型的影响规律。实验结果表明：水平管内插入多孔板后,分层/塞状流转变边界向液相流量增大方向推移,塞状/泡状流转变边界向液相流量减小方向推移;随气相流量减小或液相流量增大,多孔板后流型趋于形成泡状流;孔径大小对多孔板后流型具有重要影响,减小孔径使塞状/泡状流转变边界移向更大气相流量和更小液相流量,即形成泡状流的两相流量范围增大;随孔径减小,孔板后流型趋于由分层流直接过渡至泡状流,塞状流趋于消失。为保证多孔板吸收装置的良好流型和吸收效果,建议多孔板孔径不大于3 mm。     

水平管稠油掺气减阻模拟实验

依托流体可视化环道装置,设计并加工稠油掺气减阻模拟装置,实验研究水平管内两种稠油模拟油掺气流动阻力特性,拍摄不同气液流量比下的管流流型,分析不同实验条件下气相对稠油的减阻效果并建立相应的压降预测模型。结果表明：在气液比0~15范围内,共观察到六种流型,分别是泡状流、弹状流、分层流、段塞流、环状流、雾状流。220^#与440^#模拟油所对应的管路减阻率分别在气液比1.17和0.96时达到最大值48.19%和33.76%,当掺气比为0.9~1.2时,减阻率均可维持在20%以上。其机理可归结为空气使油-油接触转变为油-气-油接触,降低了混合相的层间剪切应力。Dukler法不适用于高黏气液两相流,所建立的稠油-气两相压降模型预测值与实测值吻合良好,平均相对误差在20%以内。     

The calibration of a timbrell aerosol spectrometer

An experimental method for the calibration of a Timbrell aerosol spectrometer is described and the influence of the aerosol and winnowing air flow rates on performance investigated. The Timbrell spectrometer size classifies airborne particles according to their aerodynamic diameters, winnowing them in a recirculating flow of clean air while they fall under the influence of gravity in a horizontal settling chamber. Size separation takes place under Stokesian conditions and the particles deposit on to a series of microscope slides. The results of the calibration with monodisperse polymer latex microspheres and polydisperse spherical particles of polyvinyl acetate show that the instrument achieved acceptable size resolution (12%) at an aerosol sampling flow rate of 1 cm³ min⁻¹, with a ratio of aerosol to winnowing flow rate of 6.7 × 10⁻³. Under the conditions used the instrument was shown to be most sensitive for size classifying particles in the range 4–12 μm aerodynamic diameter. The Timbrell aerosol spectrometer is a useful device both as a reference method for the determination of aerodynamic diameters of airborne particles and as a means of collecting such particles for subsequent examination by other aerosol analysis equipment.     

聚丙烯颗粒密相脉冲气力输送影响因素实验研究

在一输送管线水平长１９ｍ，垂直长１１ｍ，内径５０ｍｍ的密相脉冲气力输送实验台上进行了聚丙烯的输送研究，实验结果表明：气刀的操作周期、充气时间与断气时间的比值对输送气速、输送能力、固气比、能耗等均有明显影响     

油气水三相流流型的灰度波动时间序列分析

三相流流型极大地影响三相流的流动和传热特性,准确表征流型对相关设备的设计和运行具有重要意义。在水体积流量为1.32—12.15 m3/h,油体积流量为0.01—0.43 m3/h,空气体积流量为0.75—2.5 m3/h时,对垂直上升管中油气水三相流的6种典型流型进行了动态图像的拍摄,提取每一帧图像的灰度均值组成灰度波动信号,进行了分形及混沌时间序列分析。分析结果为:当空气流量在0.75—2.5 m3/h之间变化时,所提取的分形维数及吸引子关联维数分别在0.924 7—1.223 4及1.493 7—5.498 2之间,且分形维数及混沌吸引子关联维数随气相流量呈不规则突变,并与流型的Wigner-Ville分布(WVD)特征相对应,表明了分形维数及混沌吸引子关联维数对油气水三相流流型变化具有敏感的"指示器"特性,可以较好地表征油气水三相流流型变化。     

带芯管的管式反应器中流体力学的实验研究

本文以电石法聚氯乙烯生产流程中的转化器为背景,提出在转化器列管内加入芯管的改进方案,改变管内物料的流动状态及温度分布,以提高反应器的生产能力。通过实验测量反应器入口与各出口流速及压差,计算出空气在其中流动时夹层及开孔处的阻力系数。实验表明在相同的入口流量下,空气进入夹层,分别从芯管和夹层同时流出时,芯管开孔直径越大,芯管与夹层的出口流量比增大;在相同的孔径的条件下,随着入口流量的增加,夹层和芯管的出口流量差值减小。并根据实验数据拟合了空气流经开孔的阻力系数公式。     

A New Technique for Spray-Dried Encapsulation of Lycopene

A new technique for lycopene microencapsulation by spray drying using dehumidified air as the drying medium was developed and the optimum operating conditions for encapsulation efficiency were determined. A pilot-scale spray dryer was employed for the spray-drying process. The modification made to the original design consisted of connecting the dryer inlet air intake to an absorption air dryer. The dextrose equivalent (DE) of maltodextrin, ratio of core to wall material, feed temperature, inlet air temperature, drying air flow rate, and compressed air flow rate were the factors investigated with respect to encapsulation efficiency. The resulting microcapsules were evaluated in terms of moisture content, bulk density, rehydration ability, lycopene isomerization, and storage stability. The optimum operating conditions were found to be as follows: ratio of core to wall material, 1:3.3; feed temperature, 52°C; inlet air temperature, 147°C. Under these conditions, the maximum encapsulation efficiency was about 93%. The use of dehumidified air was proven to be an effective way of increasing lycopene encapsulation efficiency.     

大差异颗粒分级再生设备的性能研究

通过改变表观气速U、颗粒循环速率W、粉尘/捕集颗粒比R等操作参数,考察了大差异颗粒空气分级设备在设置内构件前后的压降和分级效率的变化。结果表明,自由床时,压降随表观气速的增大而增大,分离效率在U=0.27 m/s时达到最大值87%。捕集颗粒循环量对压降的影响较小,分级效率随W的增大而持续下降。粉尘/捕集颗粒比较低时,压降无变化,但增大至超过约翰逊网的阻塞限度后,操作压降呈指数型增长,分级效率迅速下降。设置内构件后,由于其起到了整流和分布作用,设备压降和分级效率的变化不如自由床时敏感,拓宽了可操作的粉尘/捕集颗粒比范围,但缩小了可操作的表观气速范围。将设备实际压降划分为约翰逊网压降、颗粒摩擦压降、气体出口压降三个部分,基于实验结果,给出了计算压降的模型。