A model for predicting bubble rise velocity in a pulsed gas solid fluidized bed

Bed stability, and especially the bed density distribution, is affected by the behavior of bubbles in a gas solid fluidized bed. Bubble rise velocity in a pulsed gas-solid fluidized bed was studied using photographic and computational fluid dynamics methods. The variation in bubble rise velocity was investigated as a function of the periodic pulsed air flow. A predictive model of bubble rise velocity was derived: ub=ψ(Ut+Up-Umf)+kp(gdb)(1/2). The software of Origin was used to fit the empirical coefficients to give ψ = 0.4807 and kp = 0.1305. Experimental verification of the simulations shows that the regular change in bubble rise velocity is accurately described by the model. The correlation coefficient was 0.9905 for the simulations and 0.9706 for the experiments.

Method of temperature rising velocity and threshold control of electron beam brazing

In order to accommodate electron beam to the brazing of the joints with various curve shapes and the brazing of thermo sensitive materials, the method of electron beam scanning and brazing temperature control was developed, in which electron beam was controlled to scan according to predefined scanning track, and the actual temperature rising velocity of the brazed seam was lim- ited in an allowed scope by detecting the brazed seam temperature, calculating the temperature rising velocity and adjusting the beam current during the brazing process; in addition, through the setting of the highest allowed temperature, the actual temperature of the brazed seam could be controlled not exceeding the threshold set value, and these two methods could be employed alone or jointly. It is shown that high precision temperature control in electron beam brazing could be realized and the productivity be increased by the proposed method.

Prediction of Fluid Velocity Distribution near a Rising Bubble

A model is presented for predicting the fluid velocity distribution around a rising bubble which startsfrom rest on a distillation column tray by considering the unsteady fluid flow based on the method of streamfunction. Experimental measurement of the velocity distribution by using whole field digitized PIV (particle imagevelocimetry) method is briefly described. The velocity distribution predicted by the present model is in betteragreement with the measurements than the others models published in literature.

Temperature Rise Calculation and Velocity Planning of Permanent Magnet Linear Synchronous Motor under Trapezoidal Speed

For permanent magnet linear synchronous motor(PMLSM) working at trapezoidal speed for long time, high thrust brings high temperature rise, while low thrust limits dynamic performance. Thus, it is crucial to find a balance between temperature rise and dynamic performance. In this paper, a velocity planning model of the PMLSM at trapezoidal speed based on electromagnetic-fluid-thermal(EFT) field is proposed to obtain the optimal dynamic performance under temperature limitation. In this model, the winding loss is calculated considering the acceleration and deceleration time. The loss model is indirectly verified by the temperature rise experiment of an annular winding sample. The actual working conditions of the PMLSM are simulated by dynamic grid technology to research the influence of acceleration and deceleration on fluid flow in the air gap, and the variation rule of the thermal boundary condition is analyzed. Combined with the above conditions, the temperature rise of a coreless PMLSM(CPMLSM) under the rated working condition is calculated and analyzed in detail. Through this method and several iterations, the optimal dynamic performance under the temperature limitation is achieved. The result is verified by a comparison between simulation and prototype tests, which can help improve the dynamic performance.

A new model for predicting the critical liquid-carrying velocity in inclined gas wells

Based on the assumption of gas-liquid stratified flow pattern in inclined gas wells,considering the influence of wettability and surface tension on the circumferential distribution of liquid film along the wellbore wall,the influence of the change of the gas-liquid interface configuration on the potential energy,kinetic energy and surface free energy of the two-phase system per unit length of the tube is investigated,and a new model for calculating the gas-liquid distribution at critical conditions is developed by using the principle of minimum energy.Considering the influence of the inclination angle,the calculation model of interfacial friction factor is established,and finally closed the governing equations.The interface shape is more vulnerable to wettability and surface tension at a low liquid holdup,resulting in a curved interface configuration.The interface is more curved when the smaller is the pipe diameter,or the smaller the liquid holdup,or the smaller the deviation angle,or the greater gas velocity,or the greater the gas density.The critical liquid-carrying velocity increases nonlinearly and then decreases with the increase of inclination angle.The inclination corresponding to the maximum critical liquid-carrying velocity increases with the increase of the diameter of the wellbore,and it is also affected by the fluid properties of the gas phase and liquid phase.The mean relative errors for critical liquid-carrying velocity and critical pressure gradient are 1.19%and 3.02%,respectively,and the misclassification rate is 2.38%in the field trial,implying the new model can provide a valid judgement on the liquid loading in inclined gas wells.

Hydrodynamic Behavior of a Single Bubble Rising in Viscous Liquids

The rising behavior of single bubbles has been investigated in six systems with different viscosity and Morton number(Mo) from 3.21×10-11 to 163. Bubbles with maximum equivalent diameter of up to 16 mm were investigated. The bubble Reynolds number(Re) ranged from 0.02 to 1200 covering 3 regimes in which two func-tions are obtained relating the drag coefficient,CD,with Re and Mo. It has been found that in the high Reynolds number regime the drag coefficient increases until the Reynolds number of about 1200. The classic expression of Jamialahmadi(1994) is improved and extended to high viscosity liquids. A new relationship for the aspect ratio of deformed bubbles in terms of Re,the Etvs number and Mo,applicable to a wide range of system properties,espe-cially in high viscosity liquids,is also suggested.

Interaction of two in-line bubbles of equal size rising in viscous liquid

The interaction of bubbles is the key to understand gas–liquid bubbling flow. Two-dimensional axis-symmetry computational fluid dynamics simulations on the interactive bubbles were performed with VOF method,which was validated by experimental work. It is testified that several different bubble interactive behaviors could be acquired under different conditions. Firstly, for large bubbles(d: 4, 6, 8, 10 mm), the trailing bubble rising velocity and aspect ratio have negative correlations with liquid viscosity and surface tension. The influences of viscosity and surface tension on leading bubble are negligible. Secondly, for smaller bubbles(d: 1, 2 mm), the results are complicated. The two bubbles tend to move together due to the attractive force by the wake and the potential repulsive force. Especially for high viscous or high surface tension liquid, the bubble pairs undergo several times acceleration and deceleration. In addition, bubble deformation plays an important role during bubble interaction which cannot be neglected.

Evidences of the expanding Earth from space-geodetic data over solid land and sea level rise in recent two decades

According to the space-geodetic data recorded at globally distributed stations over solid land spanning a period of more than 20-years under the International Terrestrial Reference Frame 2008,our previous estimate of the average-weighted vertical variation of the Earth＇s solid surface suggests that the Earth＇s solid part is expanding at a rate of 0.24 ± 0.05 mm/a in recent two decades.In another aspect,the satellite altimetry observations spanning recent two decades demonstrate the sea level rise（SLR） rate 3.2 ± 0.4 mm/a,of which1.8 ± 0.5 mm/a is contributed by the ice melting over land.This study shows that the oceanic thermal expansion is 1.0 ± 0.1 mm/a due to the temperature increase in recent half century,which coincides with the estimate provided by previous authors.The SLR observation by altimetry is not balanced by the ice melting and thermal expansion,which is an open problem before this study.However,in this study we infer that the oceanic part of the Earth is expanding at a rate about 0.4 mm/a.Combining the expansion rates of land part and oceanic part,we conclude that the Earth is expanding at a rate of 0.35 ± 0.47 mm/a in recent two decades.If the Earth expands at this rate,then the altimetry-observed SLR can be well explained.

Analysis of the rising and sinking movement of the crust in Qinghai－Xizang Plateau，China

The average swelling height of Qinghai-Xizang Plateau(Tibet) is about 4.1 km.The area is about 2 300 000 km2.It is the highest and the largest plateau in the world.Mount Qomolangma,the highest peak in the world,is located in the southern fringe of the plateau,and its height is still increasing.What is the driving force for the rising of the Qinghai-Xizang plateau?How high will the plateau still rise from now on? These questions are much concerned by people.In this paper the distribution of the pressure at different depths in the region of Qinghai-Xizang Plateau are derived according to the three-dimensional structures of the S-wave velocity in the crust and upper mantle.The crust and upper mantle structures of the Qinghai-Xizang Plateau is deliberated on the basis of the distribution with a comprehensive analysis on the rock types,earthquakes and the relative crust movements.Then the two questions raised above are discussed.

半U形隧道火灾补气速度和最高烟气温升的机器学习预测

半U形隧道是考虑火灾发生在水下隧道变坡点前而简化得到的隧道结构,通过理论推导很难建立有关烟气运动参数预测模型。因此,借助于FDS数值模拟和机器学习对320组火灾工况进行模拟分析和机器学习预测。结果表明:纵向风速的增大对于空气补充速度会有一定的抑制效果,BP神经网络在测试集和训练集上的预测效果较其他机器学习模型更为精确,决定系数R~2能够达到0.99;通过Shap值对影响隧道内空气补充速度的特征因素按重要性从高到低排序依次为高度效应、热效应、风效应;最高烟气温升受风速影响,坡高小则温升随风速减小剧烈,坡高大时风速影响不显著,并且相较于其他机器学习方法,BP神经网络和理论计算均能准确预测烟气最高温升,R~2均大于0.9。研究结合数值模拟与机器学习,为高效预测隧道火灾动力学行为及通风排烟系统优化设计提供了新方法。

升降速率对内浮盘运行稳定性影响的实验探究

浮盘是覆盖在罐内储存介质上并随液面升降的盘状物结构,可以极大地减少罐内储存介质的挥发损耗,降低储罐发生火灾的风险。储罐不同收发油作业工况所引起的浮盘升降速度的变化会对浮盘运行的稳定性产生较大影响。文章通过利用两座工业尺寸储罐(容积300 m3,内径6500 mm)以及全浸液式浮盘,探究了不同升降速度条件下浮盘倾角的变化规律。实验发现在浮盘升降过程中,与储罐进出液口处于平行方向位置上浮盘的倾角较大,处于垂直方向位置处则几乎没有倾角,最大倾角出现在浮盘启停时。此外,浮盘升降过程中倾角的平均值与最大值的绝对值均与浮盘的升降速度呈现正相关关系。

柴油氧化催化器性能的影响因素研究

基于发动机台架进行柴油氧化催化器性能试验,研究了在发动机正常运转时DOC温升特性,出口温度变化受到空速和DOC入口温度的影响。空速(Space Velocity)、DOC入口排气温度对NO、CO和碳氢化合物对转化效率的影响,结果表明,在NO转化效率上1#DOC在250~450℃下空速越低转化效率越好,其中在175~350℃下转化效率随着温度得升高而增加,在375~450℃中转化效率随着温度升高而下降。2#DOC中可以看出在低温区域(175~275℃)空速越高转化效率越好,在300~450℃下空速越低转化效率越好。不同类型DOC对CO的转化效率在各温度下均在90%以上。两种DOC的THC转化效率1#DOC在300~400℃转化效率最高为90%,2#DOC在275~400℃转化效率最高为80%。

低矮建筑风驱雨压分布特性及其机理分析

采用欧拉-欧拉多相流模型,在利用实测数据验证数值方法的基础上,对TTU单体低矮建筑进行在风雨共同作用下的风雨场模拟,对比分析9种风驱雨工况下风速和雨强与低矮建筑迎风墙面最大风驱雨压之间的关系;对群体低矮建筑在不同布局、不同间距的工况下进行风驱雨压数值模拟,分析WDR雨压分布特性及气动干扰效应下群体建筑风驱雨压特性存在差异的主要原因。基于风雨流场对风驱雨压特性的机理分析可知,气流在前后排建筑之间形成漩涡,风驱雨压在等高区域较单体有所减小,两侧明显增加;气流在左右列建筑之间进行交汇,气流挤压造成建筑内侧风驱雨压高于建筑外侧。单、群体低矮建筑的最大WDR荷载可分别达到纯风荷载的13.39%、 30.03%。结果表明:风雨场中的雨相附加荷载不容忽视,在结构设计时应考虑建筑顶部的荷载验算,提高设计强度。此外,群体建筑布局应适当增加安全间距,避免气流阻塞效应造成的不利影响。

低矮房屋的风载特性--近地风剖面变化规律的研究

在风灾过程中,许多高度在10m以下的低矮房屋遭到破坏或损毁。为深入了解这类低矮房屋的风载及近地风场特征,基于2005年台风"达维"、2007年热带风暴"范斯高"及季风观测的部分实测数据,对比分析这三种不同风场在离地面为10m、7.5m及6m不同高度处的平均风速及风向、湍流度和阵风因子等风场特征参数。提出针对低矮房屋在不同高度处平均风速及湍流度的变化规律。在此基础上,结合对原型低矮房屋实测数据的分析,验证该规律的可行性,其结果可为改进低矮房屋的抗风设计提供有价值的参考。

普通民房在爆破地震波作用下的振动破坏分析

爆破地震波作用于房屋结构体所产生的连续拉扭及超载作用将造成房屋墙面抹灰脱落、结构体裂缝开裂延伸等现象。在各振动物理量中 ,振动速度中的径向振动分量持续时间长、主频低且接近于房屋结构体自振频率 ,且楼体高层处径向振动速度分量相对于低楼层的有明显放大 ,放大系数β=1 .5 ,经分析认为爆破地震波中的径向速度分量在结构物破坏中是一个主要的因素。通过长期的爆破震动时结构物振动响应数据采集分析及结构体裂缝现象观测 ,提出了适宜某场区实际特征的普通民房结构体的容许振动速度标准v=2

CANON颗粒污泥高效脱氮及处理生活污水实验研究

为研究全程自养脱氮(CANON)颗粒污泥高效脱氮及处理生活污水的可行性,应用SBR反应器,首先在高氨氮条件下,通过搅拌快速启动CANON颗粒污泥,然后通过提高污泥质量浓度短时间内快速提升脱氮效能,最后研究了该工艺在生活污水中应用的可行性.结果表明:CANON颗粒污泥在40 d内成功启动,126 d颗粒粒径为760μm,负荷达1.01 kg/(m3·d),多糖与蛋白质比值变化与粒径增长相关;通过外加颗粒污泥,77 d内总氮去除负荷迅速提高到3.22 kg/(m3·d);在处理生活污水实验中实现了氮素和有机物的同步去除,可以有效应用于常温生活污水脱氮.

静水中气泡上升运动特性的数值模拟研究

采用数值模拟和实验研究相结合的方法,对静水中气泡上升运动特性进行了研究。在考虑和不考虑Basset力的情况下对推导出的静水中单个气泡上升运动控制方程进行耦合求解的基础上,对比分析了不同初始半径气泡上升速度模拟值与实测值之间的差异,研究了在考虑Basset力的情况下静水中不同初始半径气泡的模拟上升速度与时间的关系以及上升速度和初始半径对气泡半径变化率的影响。

冷却水流速对汽车水冷电机温升影响研究

为获得水冷电机的最佳流速,基于传热学及流体力学理论推导了水冷电机的冷却水流速与电机内部温度的关系。冷却水层流时,电机温度随着流速的增大下降明显;冷却水紊流后,对电机冷却效果进一步增强,但随流速继续增大,电机温度降低程度随冷却水流量增加将出现热饱和;建立了水冷感应电机热网络模型,基于此模型计算了电机额定负载运行稳态温升及不同流速时电机绕组及定子轭部的温度分布;实验测试了样机额定运行及不同冷却水流速时的电机温升。仿真及实验结果与理论分析结果相一致,验证了理论推导的正确性,为水冷电机选择合理的冷却水流速提供参考依据。

黏性流体中单气泡的运动特性

采用高速CCD成像技术实验测定了单个气泡在水及不同黏度甘油水溶液中的形变特性及上升终速度。结果表明,随着液相黏度的增加,小气泡均能呈良好球形,而大气泡则由类似椭球形的不规则形状逐渐向球帽形转变;气泡的周期性振荡趋于平缓,气泡上升终速度降低。提出了计算气泡上升终速度的关联方程,其预测结果与实验值吻合良好。

气泡之间相互作用的数值模拟

该文采用VOF(Volume-of-Fluid)中的PLIC(Piecewise Linear Interface Calculation)界面重构方法模拟研究了不同放置方式气泡之间的相互作用,重点分析了外围流体黏性及气泡间距对其影响。结果表明,外围流体黏性及气泡间距对气泡的融合及上升速度都具有不同程度的影响,气泡水平放置时,泡间距较小时,气泡上升速度比单个要大。在气泡开始融合到此过程结束的同时,上升速度出现了先降低后反弹的现象,且随着雷诺数的增加速度降低开始时间滞后。