垂直同心环形管内上升气液两相环状流含气率与压降预测

对垂直同心环形管内上升气液环状流的截面含气率及压降预测进行了研究.根据Kelessidis有关团状流向环状流转换的思路以及Wallis有关圆管内环状流积分分析的方法,考虑环形管的结构特征及环状流的流型特征,通过两相动力学理论建立了新的预测截面含气率及总压降的模型.将新模型及现有模型与实验数据的分析比较表明新模型对于总压降的预测效果较好.     

基于旋转分相单元的电容式气液两相流含液率测量

为提高电容器对含水率测量的能力,设计与其相匹配的旋转分相单元,以实现气液两相流含水率的起旋分相式电容测量。在电容传感器的测量单元基础上,增加旋转分相单元,利用气液两相流体力学理论对其结构进行设计优化,并根据实际应用条件确定分离圈数,保证气液分相效率。旋转分相单元克服了气液两相流流动形态的多样性,将体积含水率信息转换成液膜厚度信息及截面含水率信息进行测量。经实验验证,Lockhart-Martinelli截面含气率模型与实验中电容器测量截面含气率具有良好的一致性,其能够实现对体积含水率20%以内的气液两相流有效测量,体积含水率的绝对误差在±2%以内。     

矩形截面螺旋通道内气液两相流局部含气率分布实验研究

应用电导探针测量技术,对矩形截面螺旋通道内气液两相流局部含气率进行实验研究。在不同的气相折算速度下,应用电导探针测量了弹状流弹单元的长度,并与可视化方法进行对比,验证了电导探针的可靠性,并为信号处理选择合适的阈值。分别在泡状流、弹状流及环状流三种流型的条件下,分析了气相与液相折算速度对局部含气率分布的影响。实验结果发现,螺旋通道气液两相局部含气率呈非对称的抛物线形分布,这种非对称性受流型和液相折算速度的影响。     

基于旋转分相单元的电容式气液两相流含液率测量

为提高电容器对含水率测量的能力,设计与其相匹配的旋转分相单元,以实现气液两相流含水率的起旋分相式电容测量。在电容传感器的测量单元基础上,增加旋转分相单元,利用气液两相流体力学理论对其结构进行设计优化,并根据实际应用条件确定分离圈数,保证气液分相效率。旋转分相单元克服了气液两相流流动形态的多样性,将体积含水率信息转换成液膜厚度信息及截面含水率信息进行测量。经实验验证,Lockhart-Martinelli截面含气率模型与实验中电容器测量截面含气率具有良好的一致性,其能够实现对体积含水率20%以内的气液两相流有效测量,体积含水率的绝对误差在±2%以内。     

水平管束间气液两相流局部含气率分布的实验研究

在废热锅炉火管管束间的气液两相流中,局部含气率的分布直接影响管束间流场、温度场的均匀性以及火管壁温工况.使用单纤光纤探针对水平管束间含气率的分布进行测量.实验沿管周方向以5度的间隔布置测点,得出含气率随径向、角度、气量、液量等参数变化的分布规律.同时通过分析得到了平均截面含气率的计算式.     

矩形截面螺旋通道内气液两相流局部含气率分布实验研究

应用电导探针测量技术,对矩形截面螺旋通道内气液两相流局部含气率进行实验研究。在不同的气相折算速度下,应用电导探针测量了弹状流弹单元的长度,并与可视化方法进行对比,验证了电导探针的可靠性,并为信号处理选择合适的阈值。分别在泡状流、弹状流及环状流三种流型的条件下,分析了气相与液相折算速度对局部含气率分布的影响。实验结果发现,螺旋通道气液两相局部含气率呈非对称的抛物线形分布,这种非对称性受流型和液相折算速度的影响。     

正方形小通道内气液两相流垂直向上流动特性

辅助高速摄影仪对正方形小通道内氮气-水两相流向上流动进行可视化观察,对流动特性进行了实验研究,获得了典型的流型图像。采用数字图像处理技术对流型图像进行了处理,检测得到气相的周长、面积,并通过提出的假想圆柱体模型计算和统计得到了截面含气率。将压降实验数据分析结果与典型的分相流、均相流压降模型预测值比较,结果表明,Chisholm关系式能较好地预测两相流的压降变化,Lee & Lee关系式和Dukler关系式可较好地预测低表观速度时的两相流压降。     

带有Kenics静态混合器的水平液固两相流化床换热管的压降研究

以饱和硫酸钙为介质,在安装Kenics静态混合器的水平液固两相流化床换热管上进行实验研究,考察介质流速、Kenics静态混合器扭率、颗粒体积分数及颗粒尺寸对压降的影响,并与冷态实验条件下的压降变化规律进行比较。结果表明：同等操作条件,安装Kenics静态混合器后压降比安装前提高20%～140%;压降随雷诺数的增大而增大,随Kenics静态混合器扭率的增大而减小;颗粒体积分数对压降也有影响。根据实验数据,得出了稳定操作条件下压降与上述影响因素之间的经验关联式,为带有Kenics静态混合器的水平液固两相流化床换热器的设计提供计算依据。     

气液两相流中顺列管束涡街特性实验研究

对受气液两相流横向冲刷的顺列管束旋涡脱离特性进行了实验研究。实验中通过测量顺列管束所受升力的频谱特性来确定涡街的脱离频率。实验中来流雷诺数的范围为 1.6× 10 4～ 8× 10 4,截面含气率的范围为 0～ 0 .30 ,横向管间距比 T/ D=1.5、 2 .0、 3.0 ,纵向管间距比 P/ D=2 .0、 3.0、 4.0。实验结果揭示了顺列管束涡街特性和斯特罗哈数随含气率、管间距、两相雷诺数的变化规律     

无泄漏的管壳式换热器壳侧局部含气率的研究

在常温常压下 ,应用电导探针对无泄漏的TEMA -E型管壳式换热器壳侧气液两相流的局部含气率进行了测量 ,研究发现在壳侧错流区折流板的迎流面和背流面附近 ,气液分布有着明显的差异 ,而且两者均不等同于错流区中心区域的气液分布。通过对局部含气率的加权体积积分得到了体积平均含气率 ,并采用马蒂内利参数及全液相佛鲁德数进行关联 ,得到的关联式与实验数据较吻合     

多元混合气体在硅橡胶膜中的渗透传质研究

以O2、N2和Co2单组分及其多元混合气为目标气体,系统研究了他们在硅橡胶膜中的渗透传质行为,考察了压差和进气组成等因素对渗透通量和透过气组成的影响。实验结果表明,气体渗透通量随着压差的升高而增加,渗透快的气体在透过气中的含量也随着压差的升高而增加;透过气中慢气N2的体积分率总是低于其在进气中的体积分率,快气CO2的变化与之相反,而透过气中O2的体积分率可能高于也可能低于其在进气中的体积分率,取决于混合气中其他组分的性质及相互比例关系。     

基于截面气含率的文丘里湿气压降模型

运用两相流理论对湿气中的气相与液相流动进行分析,在分层流与环雾状流的条件下推导了两相流通过水平标准文丘里流量计的理论模型.通过分别考虑截面气含率、相间摩擦以及液滴夹带等因素,在文丘里轴向对湿气流动中的气相动量方程进行求解.通过对水平直管中的截面气含率公式进行修正,建立了适用于收缩管道的截面气含率模型,并在此基础上模拟了湿气流经标准文丘里时其两个取压孔之间的轴向静压分布.实验证实,使用修正后的截面气含率公式将使模型对文丘里压降的预测准确度明显提升,其相对误差在15%以内.该模型以湿气两相流在水平文丘里中的流动形态为依据,具有较充分的物理背景,而且在推导过程中较少依赖特定实验装置与数据,为建立具有一定普适性的文丘里湿气计量模型奠定了基础.     

超音速喷管内准一维气相流动建模与数值模拟

通过理论分析建立考虑壁面摩擦和换热影响的喷管内气相准一维流动数理模型，在气动方程组矢通量分裂基础上，采用有限差分方法对其变体形式进行离散，空间导数采用五阶精度WENO格式，时间导数采用三阶精度三步TVD龙格库塔方法，在Fortran平台上进行编程和计算，进行模型方法验证和参数研究。结果表明，在适当选取摩擦修正因子时，数值模拟与实验数据吻合较好，验证了数理模型、数值计算与求解方法的有效性。喷管半扩张角增大时，出口气流速度和马赫数增大，而静压减小；进口总温提高时，出口速度显著升高，但由于壁面摩擦和换热加剧，相应的出口马赫数会减小；进口总压提高时，出口气流速度并不显著增大；壁面温度升高时，出口气流速度和马赫数均减小。     

Magneto-piezoresistive characteristics of graphene/room temperature vulcanized silicon rubber-silicon rubber magnetorheological elastomer

The effect of graphene with different content on the magneto-piezoresistive characteristics of graphene/room temperature vulcanized silicon rubber (GR/RTV) magnetorheological elastomer (MRE) was studied, and the relationship between the content of graphene and conductivity of GR/RTV-MRE was described based on the general effective medium theory. A magneto-piezoresistive model was established to describe the relationship among resistance, pressure, and magnetic field based on the magnetic dipole and tunneling theory. The samples of GR/RTV-MRE with different content of graphene were prepared. The experimental platform with magneto-piezoresistive characteristics controlled by magnetic field was built. The effect of graphene with different content on piezoresistive coefficient of GR/RTV-MRE was obtained under different magnetic flux density. The experimental results showed that the piezoresistive coefficients of samples with different content of graphene decrease with the increase of magnetic flux density in the range of 0 ~ 80mT. For the same magnetic field, when the volume fraction of graphene is less than 12%, the piezoresistive coefficient is positively correlated with it, when the volume fraction of graphene is more than 12%; the increase of content has little effect on the piezoresistive characteristics. The experimental results are compared with theoretical calculations for correction and error analysis. The results showed that the modified model can well describe the variation of the resistance of GR/RTV-MRE under magnetic field and pressure.     

Two-dimensional transient numerical simulation of solids and gas flow in the riser section of a circulating fluidized bed

A computational fluid dynamics software (CFX) was modified for gas/particle flow systems and used to predict the flow parameters in the riser section of a circulating fluidized bed (CFB). Fluid Catalytic Cracking (FCC) particles and air were used as the solids and gas phases, respectively. Two-dimensional, transient, isothermal flows were simulated for the continuous phase (air) and the dispersed phase (solid particles). Conservation equations of mass and momentum for each phase were solved using the finite volume numerical technique. Two-dimensional gas and particle flow profiles were obtained for the velocity, volume fraction, and pressure drop for each phase. Calculations showed that the inlet and exit conditions play a significant role in the overall mixing of the gas and particulate phases and in the establishment of the flow regime. The flow behavior was analyzed based on the different frequency of oscillations in the riser. Comparison of the calculated solids mass flux, solids density and pressure drop with the measured pilot-scale PSRI data (reported in this paper) showed a good agreement.     

TWO-DIMENSIONAL TRANSIENT NUMERICAL SIMULATION OF SOLIDS AND GAS FLOW IN THE RISER SECTION OF A CIRCULATING FLUIDIZED BED

A computational fluid dynamics software (CFX) was modified for gas/particle flow systems and used to predict the flow parameters in the riser section of a circulating fluidized bed (CFB). Fluid Catalytic Cracking (FCC) particles and air were used as the solids and gas phases, respectively. Two-dimensional, transient, isothermal flows were simulated for the continuous phase (air) and the dispersed phase (solid particles). Conservation equations of mass and momentum for each phase were solved using the finite volume numerical technique. Two-dimensional gas and particle flow profiles were obtained for the velocity, volume fraction, and pressure drop for each phase. Calculations showed that the inlet and exit conditions play a significant role in the overall mixing of the gas and particulate phases and in the establishment of the flow regime. The flow behavior was analyzed based on the different frequency of oscillations in the riser. Comparison of the calculated solids mass flux, solids density and pressure drop with the measured pilot-scale PSRI data (reported in this paper) showed a good agreement.     

颗粒黏度模型对采用欧拉多相流模型模拟超密相颗粒流动行为的影响

颗粒黏度是欧拉多相流模型计算固体流动的重要参数之一,其数值大小依赖于摩擦压力和径向分布函数。通过与实验值对比,评估了常用的摩擦压力模型（Based、Johnson）和径向分布函数模型（Lun、Syamlal O’Brien）对密相颗粒流动体系的预测能力。模拟结果表明,Johnson模型的固体体积分数预测值低于Based模型;Syamlal O’Brien 模型固体流率的预测值远大于Lun模型。采用根据实验结果修正的欧根系数后,Based-Lun、Johnson-Lun和Johnson-SO模型组合预测的平均压降相对误差分别由68.6%、73.3%和78.2%降低至13.2%、29.7%和42.3%。综合考虑压降、固体出口质量流率、固体体积分数、壁面区域固体速度的模拟结果与实验值的偏差,发现Based-Lun模型组合的平均预测误差最小,适用于气固移动床的欧拉多相流模拟。研究还发现,欧根系数与内摩擦角对固体速度与压降有着显著的影响,而临界固含率对固体速度与压降的影响较小。     

Prediction of Nusselt Number and Friction Factor of Water-Al2O3 Nanofluid Flow in Shell-and-Tube Heat Exchanger with Helical Baffles

Heat transfer and flow field of water-Al₂O₃ nanofluid were simulated three-dimensionally in the shell-side of shell-and-tube heat exchanger with helical baffles. The effects of Reynolds number and volume fraction on heat transfer and pressure drop were evaluated. Increasing the volume fraction and Reynolds number intensified both heat transfer and pressure drop. Reduction of the Reynolds number increased the friction factor, but no considerable change was observed in the friction factor by increasing the volume fraction at constant Reynolds number. Heat transfer of the nanofluid revealed greater dependency on the volume fraction of particles at lower Reynolds numbers. Models of Nusselt number and friction factor were obtained in the heat exchanger in terms of Reynolds number and volume fraction using neural network. The neural network predicted the output variables with great accuracy.     

三角形螺旋填料旋转床气相压降特性

为深入了解三角形螺旋填料旋转床气相压降的影响因素及规律,以空气-水为实验物系进行了实验和模型研究。改变气、液流量及转速测定气相压降的实验结果表明,气体流量和转速的增大均使干、湿床气相压降增大;液体流量增大时湿床气相压降先减小,而后基本保持不变;该旋转填料床具有气相压降小、操作弹性大的优点。按照气相压降产生的机理,将其分为局部压降、离心压降、转子外内腔压降和填料主体压降4部分进行模型研究,其中用旋涡理论描述转子外内腔压降、用简化的模型描述填料主体压降是新提出的方法,且所建模型能较好地描述气相压降的规律。     

竖直上升管中密相气力输送压降特性

研究了内径20 mm的竖直上升不锈钢管道中粉煤密相气力输送单位管长压降随输送参数的变化规律,并得到了Zenz相图。结果表明,在实验操作范围内管道压降主要由固相自身静压降和固相摩擦压降组成,气相产生的压降不超过总压降的1%;固相体积分数是影响压降变化的主要因素,并讨论了粉煤流速以及固相体积分数对固相静压降和摩擦压降的影响规律;考察了粉煤流速和固相体积分数对固相摩擦系数的影响,对实验数据拟合得到了固相摩擦系数的关系式,计算结果与实验值吻合较好。