加压导向管喷动流化床部分气化炉颗粒循环倍率的研究

以宽筛分的灰渣和2种不同粒径的窄筛分玻璃珠为实验原料，对加压导向管喷动流化床部分气化炉内颗粒循环倍率进行了试验研究。提出了导向管喷动流化床颗粒循环倍率和床内压降理论关系，分析了环形区的充气量在不同系统压力、导向管位置和喷动管直径对颗粒循环倍率增加因子的影响，在此基础上提出了预测颗粒循环倍率增加因子的试验关联式。结果表明：环形区充气后不仅改善了环形区的气固接触，而且显著增加了环形区和喷动区的颗粒交换，有利于床内气固非均相反应的进行。图10表1参10     

Phase splitting of a slug–annular flow at a horizontal micro-T-junction

The behavior of air–water two-phase flow at a horizontal micro-T-junction with main and side branch of 500 μm diameter was studied in this work. When the inlet flow pattern was a slug–annular flow, the impact of varying of upstream gas and liquid superficial velocity on phase distribution of two-phase flow in the T-junction was investigated in detail. It is found that the liquid taken off decreases as an increase in liquid superficial velocity, while it increases as an increase in gas superficial velocity. Liquid and gas superficial velocity have stronger impact on phase distribution when the inlet gas velocity is high. When the present data are compared to those from larger diameter T-junctions at similar inlet superficial velocities, it is found that decreasing the diameter of T-junctions increases the fraction of liquid taken off.     

水平管内油气水三相泡状流-弹状流转换的研究

结合压差波动法识别流型，对水平管内油-气-水三相泡状流-弹状流转换特性进行了理论和实验研究，建立了泡状流向弹状流转变的界线方程，结果表明，泡状流向弹状流转变的主要因素不仅包括气相折算速度和液相折算速度，而且含油率与管径也起重要作用，计算结果与实验结果基本相吻合。     

Two-phase flow patterns of nitrogen and nanofluids in a vertically capillary tube

Two-phase flow patterns of nitrogen gas and aqueous CuO nanofluids in a vertically capillary tube were investigated experimentally. The capillary tube had an inner diameter of 1.6 mm and a length of 500 mm. Water-based CuO nanofluid was a suspension consisted of water, CuO nanoparticles and sodium dodecyl benzol sulphate solution (SDBS). The mass concentration of CuO nanoparticles varied from 0.2 wt% to 2 wt%, while the volume concentration of SDBS varied from 0.5% to 2%. The gas superficial velocity varied from 0.1 m/s to 40 m/s, while the liquid superficial velocity varied from 0.04 m/s to 4 m/s. Experiments were carried out under atmospheric pressure and at a set temperature of 30 °C. Compared with conventional tubes, flow pattern transition lines occur at relatively lower water and gas flow velocities for gas–water flow in the capillary tube. While, flow pattern transition lines for gas–nanofluid flow occur at lower liquid and gas flow velocities than those for gas–water in the capillary tube. The effect of nanofluids on the two-phase flow patterns results mainly from the change of the gas–liquid surface tension. Concentrations of nanoparticles and SDBS have no effects on the flow patterns in the present concentration ranges.     

A study on the effects of operational parameters on bed-to-wall heat transfer

In this study the effects of operational parameters on bed-to-wall heat transfer in CFBs are investigated such as solids volume fraction, particle diameter, suspension density, solid circulation rate. Based on a previously developed 2D CFB model, a modified cluster renewal model is used in this investigation. The model uses the particle-based approach (PBA) and integrates the hydrodynamics and combustion aspects. The study is also validated with experimental data. As a result of this study, it is observed that the bed-to-wall heat transfer coefficients are strongly dependent on particle diameter and solids concentration at the riser wall. The smaller particles result in higher heat transfer coefficients than larger particles for the same solids volume fraction values. The heat transfer coefficient increases with suspension density. However, at a constant suspension density, the superficial velocity does not have a significant influence on the heat transfer coefficient. PBA is satisfactorily adapted to cluster renewal model so that to define the bed-to-wall heat transfer mechanisms for the upper zone.     

导流管喷动床流体动力特性的实验研究

对以小米为物料的常规喷动床及导流管喷动床全床压降随表观气速变化规律进行了实验研究．结果表明，与常规喷动床相比，导流管喷动床不仅最小喷动速度、操作压降和最大压降均大幅减小，而且夹带高度较小时会在达到稳定喷动之前发生有利于操作的不稳定喷动现象．此外，导流管喷动床的流体动力特性受料床高度影响不大，但受导流管内径和夹带高度的影响显著．最后，依据实验结果提出了导流管喷动床最小喷动速度的关联式．     

隔板式内循环流化床的流动特性研究

以石英砂和稻壳为实验床料,在隔板式内循环流化床气化炉冷态实验装置上对颗粒的内循环流动特性进行了研究,考察了高速区和低速区的流化速度、结构尺寸和侧风量等对颗粒内循环流动的影响.结果表明:在保持低速区流化速度一定的条件下,随着高速区风速增大,颗粒循环量先增大后减小;流化速度不变的条件下,颗粒循环量随孔口和侧风量的增大而增加,但增加趋势逐渐变缓.实验给出了合理的运行设计参数.通过实验数据回归,得到了石英砂和稻壳通过隔板式内循环流化床孔口的颗粒循环量关联式,计算结果与实验值误差分别小于6%和14%,能较好地预测孔口颗粒流动.     

Optical Measurement of Void Fraction and Bubble Size Distributions in a Microchannel

An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μ m diameter. By using multiple optical fibers and infrared photodiodes, void fraction, gas and liquid plug lengths, and their velocities were measured successfully. The probes responded to the passage of gas and liquid phases through the microchannel adequately so that the time-average void fraction could be obtained from the time fraction for each phase. Also, by cross-correlating the signals from two neighboring probes, the interface velocity representing gas plug velocity or ring-film propagation velocity depending on the flow pattern could be computed. Within the ranges of superficial gas and liquid velocities covered in the experiments (j _L = 0.2～0.4 m/s and j _G = 0～5 m/s), the gas plug length was found to increase with the increasing superficial gas velocity, but the liquid plug length was found to decrease sharply as the superficial gas velocity was increased; thus, the total length of the gas-liquid plug unit decreased with the superficial gas velocity.     

Numerical study on the formation of Taylor bubbles in capillary tubes

Numerical simulations have been carried out for the transient formation of Taylor bubbles in a nozzle/tube co-flow arrangement by solving the unsteady, incompressible Navier–Stokes equations. A level set method was used to track the two-phase interface. The calculated bubble size, shape, liquid film thickness, bubble length, drift velocity, pressure drop and flow fields of Taylor flow agree well with the literature data. For a given nozzle/tube configuration, the formation of Taylor bubbles is found to be mainly dependent on the relative magnitude of gas and liquid superficial velocity. However, even under the same liquid and gas superficial velocities, the change of nozzle geometry alone can drastically change the size of Taylor bubbles and the pressure drop behavior inside a given capillary. This indicates that the widely used flow pattern map presented in terms of liquid and gas superficial velocities is not unique.     

木屑在Loop seal型返料器中的流动特性研究

在冷态实验条件下,对内径为0.28m,高为10.0m的循环流化床中木屑颗粒在Loop seal返料器中的流动特性和规律进行了研究,重点考察了提升管操作气速Ug、Loop seal返料器的输送风量Q1和侧向吹风量Q2改变对颗粒循环流率Gs的影响。实验发现,改变提升管操作气速Ug对循环流率的影响不大;通过Loop seal的颗粒循环流率Gs随着输送风量Q1和侧向吹风量Q2的增加而增大;改变侧向吹风量对循环流率的影响要比改变输送风量大得多。根据实验结果,对王擎给出的循环流率Gs的计算关联式进行了修正。     

带提升管内循环流化床的流动特性研究

运行参数和结构尺寸是内循环流化床物料循环流率的重要因素。设计并搭建了内循环流化冷态试验台,通过实验分析了气化室风速、提升管风速、返料孔高度及大小对物料循环流率的影响。实验表明:物料循环流率随气化室风速、提升管风速的增大而增大,但增加幅度变化不同;随返料孔位置的增高而下降,且下降速度加快;随着返料孔面积的增大,先增大然后减小。     

An experimental study of the statistical parameters of gas–liquid two-phase slug flow in horizontal pipeline

Experiments were performed in a horizontal test loop with inner diameter 50 mm to study the gas–liquid slug flow. The translational velocities of elongated bubbles, lengths of liquid slugs and elongated bubbles, and slug frequencies were measured using two pairs of conductivity probes. Correlations are presented for elongated bubble translational velocity, length of elongated bubble and slug frequency, respectively. It was found that the translational velocity of elongated bubble is not only dependent on Froude number, but also is significantly affected by the distance from the entrance of pipeline in the higher mixture velocity range. Mean liquid slug length is relatively insensitive to the gas and liquid flow rates in the higher mixture velocity range, however in the lower mixture velocity range, the mean liquid slug length is affected by the mixture velocity. Mean slug frequency clearly increases as the liquid superficial velocity increases but it weakly depends on the gas superficial velocity.     

Local flow measurements of vertical upward bubbly flow in an annulus

Local measurements of flow parameters were performed for vertical upward bubbly flows in an annulus. The annulus channel consisted of an inner rod with a diameter of 19.1 mm and an outer round tube with an inner diameter of 38.1 mm, and the hydraulic equivalent diameter was 19.1 mm. Double-sensor conductivity probe was used for measuring void fraction, interfacial area concentration, and interfacial velocity, and laser Doppler anemometer was utilized for measuring liquid velocity and turbulence intensity. A total of 20 data sets for void fraction, interfacial area concentration, and interfacial velocity were acquired consisting of five void fractions, about 0.050, 0.10, 0.15, 0.20, and 0.25, and four superficial liquid velocities, 0.272, 0.516, 1.03, and 2.08 m/s. A total of eight data sets for liquid velocity and turbulence intensity were acquired consisting of two void fractions, about 0.050, and 0.10, and four superficial liquid velocities, 0.272, 0.516, 1.03, and 2.08 m/s. The constitutive equations for distribution parameter and drift velocity in the drift-flux model, and the semi-theoretical correlation for Sauter mean diameter namely interfacial area concentration, which were proposed previously, were validated by local flow parameters obtained in the experiment using the annulus.     

Study on gas holdup in a fluidized flotation column from bed pressure drop

This paper investigated the overall gas holdup characteristics in a cocurrent three-phase fluidized flotation column with liquid as the continuous phase. The air, water, and glass beads with a diameter of 3 mm were, respectively, used as the gas, liquid, and solid phases in the flotation column. The gas holdup studies were carried out in a plexiglass column with 0.05 m in internal diameter and 2.2 m in height. Bed pressure drop measurements were used to calculate the fractional gas holdup. During the measurements, the superficial gas and liquid velocities, respectively, varied from 0.42 to 2.55 cm/s and from 6.47 to 10.82 cm/s. Detailed experimental investigations were carried out to study the effects of static liquid height, initial static bed height, gas velocity, liquid velocity, and frother concentration on gas holdup in a cocurrent three-phase fluidized flotation column. It was found that the gas holdup increased with the flow rate of air and decreased with an increase in the water flow rate. Certain effect of the static bed height on gas holdup was observed when the gas velocity varied. But the increase in the static liquid height resulted in the decrease in gas holdup when the gas velocity varied.     

低排放燃烧室空气雾化喷嘴射流破碎特性研究

针对当前广泛应用于低排放燃气轮机燃烧室中的空气雾化喷嘴,采用大涡模拟（Large Eddy Simulation,LES）和流体体积法（Volume of Fluid,VOF）研究了其在流动模糊（Flow Blurring,FB）和流动聚焦（Flow Focusing,FF）模式下射流一次破碎过程的差异。结果表明：两种模式的射流一次破碎过程均可分为3个阶段,气液交界面波动阶段、射流发展阶段和射流破碎阶段;喷嘴内部回流区的演变决定了气液交界面的波动程度,流动模糊模式下射流在后两个阶段的径向速度和形态变化程度均远高于流动聚焦模式,气泡回流过程在其射流破碎阶段占据主导地位,液体管道内气泡分布位置与涡的强度呈正相关。     

A study into the operation of an impact‐type gas–solid separator

Gas–solid separator, a key component of a circulating fluidized bed boiler, controls the recirculation of solids around this type of boiler. As the technology matures, the drive is to have smaller size units handling a greater amount of solids. The impact separator is well suited to meet these demands with a low pressure drop from operating at low gas velocities. Complex hydrodynamics are encountered in an impact separator, where a staggered array of collection elements separates solids from an incoming mixture of gas and solid particles. The research was to examine the performance of this separator experimentally in a scale model, built to provide benchmark data. At an inlet gas velocity of 4.0 m s^?1, an overall collection efficiency of 87.5% of particles with a mean particle diameter of 125 µm was realized. The results were compared with those from a similar study. Copyright © 2004 John Wiley & Sons, Ltd.     

灯泡贯流式水轮机在小流量工况下的内流特性分析

为了研究灯泡贯流式水轮机在小流量工况下的内流特性,以某水电站贯流式水轮机为研究对象,利用RNG k-ε湍流模型对全流道进行数值计算,分析在小流量工况下尾水管恢复系数和全流道流动情况,并定量分析水轮机部分过流部件的压力脉动情况。结果表明：在小流量工况下当电站水头和导叶开度不匹配时,尾水管的恢复系数减小,当尾水管恢复系数减小2%~3%时,机组效率降低1%;受转轮主流区和尾水管死水区的相互作用,在尾水管边壁会形成漩涡结构,有明显的回流且在边壁存在高速流体;在小流量工况下,机组主要受低频压力脉动影响,转轮进口处的主频是由在转轮转动和导叶提供机组环量时产生的,在尾水管中主要受频率为0.2 Hz的低频压力脉动影响,压力脉动系数沿尾水管出口方向依次增大,最大为1.75%。     

Effect of Channel Length on the Gas–Liquid Two-Phase Flow Phenomena in a Microchannel

An optical measurement system was used to investigate the effect of microchannel length and inlet geometery on adiabatic gas–liquid two-phase flow. Experiments were conducted with 146-mm- and 1571-mm-long, circular microchannels of 100 μm diameter. Void fraction and gas and liquid plug/slug lengths and their velocities were measured for two inlet configurations for gas–liquid mixing: (a) reducer and (b) T-junction. The superficial gas velocity was varied from 0.03 to 14 m/s, and superficial liquid velocity from 0.04 to 0.7 m/s. The test section length was found to have a significant effect on the two-phase flow characteristics measured at the same axial location (37 mm from the inlet) in both microchannels. The mean void fraction data for the short (146 mm) microchannel with the reducer inlet agreed well with the equation previously proposed by Kawahara et al. (2002). On the other hand, the mean void fraction data for the long (1571 mm) microchannel obeyed the homogeneous flow model and Armand's equation for both the reducer and T-junction inlet configurations. Many long and rapidly moving gas plugs/slugs and long, slowly moving liquid plugs/slugs were observed in the short microchannel compared to the long microchannel, leading to the differences in the time-averaged void fraction data. The mean velocity of liquid plugs/slugs generally agreed well with Hughmark's equation and the homogeneous flow model predictions, regardless of the inlet configurations and microchannel lengths. Thus, both the microchannel length and inlet geometry were found to significantly affect the two-phase flow characteristics in a microchannel.     

A study on un‐fully developed slug flow in a vertical tube

Gas‐liquid co‐current vertical slug flow was studied in a vertical Plexiglas tube. Taylor bubbles and liquid slug lengths and their rising velocities were measured by means of a pair of conductivity probes under un‐fully developed flow conditions. The influences of the superficial velocity of gas and liquid on slug flow parameters were examined. Using statistical analysis on the length of Taylor bubbles, the probability distribution of the length of the Taylor bubbles was obtained, which obeyed a normal distribution under a significance level of α = 0.05. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(4): 235–242, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20063     

Inline NH3 removal from biogas digesters

During biogas production from various types of substrates such as animal manure, fats and proteins, bacterial growth and biogas production can be inhibited by excessive ammonia (NH₃) concentrations. If NH₃ is removed from the biogas digester without damaging the digestion process, inhibition of the methane (CH₄) producing bacteria will diminish. This study shows that it is possible to remove a significant quantity of NH₃ from the biogas digester headspace and liquid phase by a simple gas circulation method where gas bubbles free of NH₃ is forced through the upper 30 cm of the liquid phase in the biogas digester, into the headspace and out of the digester. The suggested method improves conditions for anaerobic bacteria exposed to high concentrations of NH₃ by simply removing NH₃ from the digester.In full-scale biogas production the system presented in this study can be improved by circulating headspace gas through an ammonia absorber and returning the NH₃ depleted biogas into the biogas digester. This method can also replace the need for mixing in biogas digesters.