文丘里洗涤器压力损失模型

通过理论分析,在考虑气体摩擦压力损失和扩散段液滴减速的压力回收基础上,推导出了一个准确、实用的文丘里洗涤器压力损失计算模型,并分别对3个具有不同喉管长度的文丘里洗涤器模型在液气比为0.4—1.0L/m3与喉管气速为33—58m/s条件下的压力损失进行了试验测量。结果表明:模型的理论预测值和试验值吻合良好,可以为工程设计或优化操作时文丘里洗涤器压力损失的预测方法。     

含内构件的循环流化床的动态压力特性

针对含内构件的循环流化床,以石英砂为物料,使用动态压力传感器测量了含内构件的流化床中气固两相流的动态压力,分析了床内的瞬时压力特性. 结果表明,在进出口总压降中,文丘里压降最大,占主床压降的60%以上. 表观气速和固体颗粒循环流率共同影响循环流化床内的压力特性. 压力瞬时波动功率谱分析表明,压力波动对应一个主频,表观气速越小、颗粒循环流率越大时,压力波动越大,且循环流化床底部压力波动比上部大. 加入内构件能有效引导气流,使流动更均匀.     

Mass transfer coefficient in the eductor liquid-liquid extraction column

In this research gasoil desalting was investigated from mass transfer point of view in an eductor liquid–liquid extraction column (eductor-LLE device). Mass transfer characteristics of the eductor-LLE device were evaluated and an empirical correlation was obtained by dimensional analysis of the dispersed phase Sherwood number. The Results showed that the overall mass transfer coefficient of the dispersed phase and extraction efficiency have been increased by increasing Sauter mean diameter (SMD) and decreasing the nozzle diameter from 2 to 1 mm, respectively. The effects of Reynolds number (Re), projection ratio (ratio of the distance between venturi throat and nozzle tip to venturi throat diameter, R_pr), venturi throat area to nozzle area ratio (R_th-n) and two phases flow rates ratio (R_Q) on the mass transfer coefficient (K) were determined. According to the results, K increase with increasing Re and R_Q and also with decreasing R_pr and R_th-n. Semi-empirical models of drop formation, rising and coalescence were compared with our proposed empirical model. It was revealed that the present model provided a relatively good fitting for the mass transfer model of drop coalescence. Moreover, experimental data were in better agreement with calculated data with AARE value of 0.085.     

Experiments in a large-scale venturi scrubber: Part I: Pressure drop

The present work details pressure drop measurements in a large-scale venturi scrubber with an inlet and throat diameters of 250 and 122.5 mm, respectively.The flow rates were varied between 0.4835 and 0.987 kg/s for the gas while the liquid was set between 0.013 and 0.075 kg/s. The results show that the pressure drop depends on both the gas and liquid phases flow rates, the droplet fraction and the method of liquid injection (spray and film).The pressure drop in the diverging section is well predicted by a boundary layer model.     

Growth of aerosol particles by adiabatic expansion at the throat of a venturi scrubber

The condensational growth of aerosol particles in the throat section of a venturi scrubber and the contribution of it to the dust collection efficiency were discussed.The condensable water vapor produced in the throat of venturi was quantitatively obtained for various conditions assuming the change in pressure and temperature to be adiabatic process. In terms of this condensable water vapor and the particle number concentration, the diameter of grown particles was determined, and the degree of contribution due to particle growth to the particle collection by venturi scrubber was evaluated as the change in particle collection efficiency involved in the particle growth.Experimental verification of the above results was qualitatively made by changing the humidity of the inlet gas, which is the most important property dominating the particle growth, in the particle collection by venturi scrubber.     

The CFD driven optimisation of a modified venturi for cavitational activity

This work presents CFD‐based optimisation of the important geometrical parameters of a cavitating venturi. The parameters for optimisation were selected based on the analysis of the steps involved in the cavitation process like cavity inception, cavity growth, and cavity collapse. It was seen that the ratio of the perimeter of the venturi to the cross‐sectional area of its constriction quantifies the possible location of the inception of the cavity. The ratio of the throat length to its height (in the case of a slit venturi) controls the maximum size of the cavity and the angle of the divergence section controls the rate of collapse of a cavity. Based on the numerical study, it was concluded that a slit venturi (α = 2.7) with the slit length equal to its height (1:1) and a half angle of divergence section of 5.5° is an optimum geometry for best cavitational activity.     

环形狭缝通道内气液两相环状流流动特性

建立了环形狭缝通道内气液两相环状流的理论模型 ,该模型计及环状流气芯流动的可压缩性、气液两相间的相滑移、气相对液滴的夹带作用等因素 .考察了两相流质量流量和干度对压降、液滴速度相对变化和狭缝喉部气芯通流面积的影响 .用建立的理论模型对空气 -水两相环状流通过环形狭缝的两相压降进行预测 ,预测值和试验值吻合良好     

Modeling hydrodynamic cavitation in venturi: influence of venturi configuration on inception and extent of cavitation

Hydrodynamic cavitation (HC) is useful for intensifying a wide variety of industrial applications including biofuel production, emulsion preparation, and wastewater treatment. Venturi is one of the most widely used devices for HC. Despite the wide spread use, the role and interactions among various design and operating parameters on generated cavitation is not yet adequately understood. This article presents results of computational investigation into the cavitation characteristics of different venturi designs over a range of operating conditions. Influence of the key geometric parameters such as the length of venturi throat and diffuser angle on the inception and extent of cavitation is discussed quantitatively. Formulation and solution of multiphase computational fluid dynamics (CFD) models are presented. Appropriate turbulence and cavitation models are selected and solved using a commercial CFD code. Care was taken to eliminate the influence of numerical parameters like mesh density, discretization scheme, and convergence criteria. The computational model was validated by comparing simulated results with three published data sets. The simulated results in terms of velocity and pressure gradients, vapor volume fractions and turbulence quantities, and so on, are critically analyzed and discussed. Diffuser angle was found to have a significant influence on cavitation inception and evolution. The length of the venturi throat has relatively less impact on cavitation inception and evolution compared to the diffuser angle. The models and simulated flow field were used to simulate detailed time–pressure histories for individual vapor cavities, including turbulent fluctuations. This in turn can be used to simulate cavity collapse and overall performance of HC device as a reactor. The presented results offer useful guidance to the designer of HC devices, identifying key operating and design parameters that can be manipulated to achieve the desired level of cavitational activity. The presented approach and results also offer a useful means to compare and to evaluate different designs of cavitation devices and operating parameters. © 2018 American Institute of Chemical Engineers AIChE J, 65: 421–433, 2019     

喷嘴洗涤器洗涤效果和压降

讨论喷嘴洗涤器除尘作用和影响除尘效果的各种因素。给出喷嘴洗涤器压降的计算方法。对两种不同的设计方案进行了计算分析，反映压降与喉管、气速和洗涤液量的关系。阐明在设计和操作中应注意的问题     

MODELING VENTURI SCRUBBER PERFORMANCE FOR PARTICULATE COLLECTION AND PRESSURE DROP

A computational model of gas-particle flows has been extended to predict venturi scrubber performance as measured by particle collection efficiency and pressure drop. The concept of regarding particle and liquid phases as sources of momentum and energy to the gaseous phase was incorporated into the model's computational scheme. Predicted pressure drop results showed good agreement with available experimental data, particularly when uniform liquid distribution across the venturi cross-section was achieved. Our model was also more successful in predicting particle collection efficiency than several other models previously reported in the literature. Differences between model predictions and experimental results were chiefly caused by maldistribution of injected liquid into the test scrubbers.     

Flow characteristics and pressure drop across the Laval nozzle in dense phase pneumatic conveying of the pulverized coal

Experimental studies were performed to describe the physical phenomena occurring in dense phase pneumatic conveying of the pulverize coal with a Laval nozzle installed in the pipeline. The maximal coal mass flow rate decreased from 0.87 kg/s to 0.35 kg/s and an obvious decrease in the solids loading ratio was revealed after the Laval nozzle was installed. In addition, the Laval nozzle showed a better capacity of resisting disturbance, which made it easier to control the coal mass flow rate precisely and promoted the stable conveying process. These specific physical phenomena were proved to result from the high pressure drop of the Laval nozzle. Thereby, a mathematic model was developed to predict the two-phase pressure drop across the Laval nozzle. The pressure drop model described the experimental data within the 15% deviation. The main influence factors contributing to the pressure drop of the Laval nozzle were discussed using the model. Then the effects of gas mass flow rate, solids loading ratio, convergence angle, throat diameter and throat length were revealed.     

Resistance Properties of a Bend in Dense‐Phase Pneumatic Conveying of Pulverized Coal under High Pressure

Experiments of high‐pressure dense‐phase pneumatic conveying of pulverized coal with different mean particle sizes using nitrogen were carried out in an experimental test facility with a conveying pressure of up to 4 MPa. The effects of three representative operating parameters (solids‐to‐gas mass flow ratio, conveying pressure, mean particle size) on the total pressure drop were examined. The pressure drops across the horizontal and vertical bends were analyzed by experimental and analytical calculation. The results show that the pressure drop due to gas friction is of much less significance, while the pressure drop due to the solids friction component of the total pressure drop dominates. There exists a relationship between the pressure drop due to solids kinetic energy loss and mass flux of solids.     

Spray and mixing characteristics of liquid jet in a tubular gas–liquid atomization mixer

For the design and optimization of a tubular gas–liquid atomization mixer,the atomization and mixing characteristics of liquid jet breakup in the limited tube space is a key problem.In this study,the primary breakup process of liquid jet column was analyzed by high-speed camera,then the droplet size and velocity distribution of atomized droplets were measured by Phase-Doppler anemometry (PDA).The hydrodynamic characteristics of gas flow in tubular gas–liquid atomization mixer were analyzed by computational fluid dynamics (CFD) numerical simulation.The results indicate that the liquid flow rate has little effect on the atomization droplet size and atomization pressure drop,and the gas flow rate is the main influence parameter.Under all experimental gas flow conditions,the liquid jet column undergoes a primary breakup process,forming larger liquid blocks and droplets.When the gas flow rate (Q_g) is less than 127 m~3·h~(-1),the secondary breakup of large liquid blocks and droplets does not occur in venturi throat region.The Sauter mean diameter (SMD) of droplets measured at the outlet is more than 140μm,and the distribution is uneven.When Q_g127 m~3·h~(-1),the large liquid blocks and droplets have secondary breakup process at the throat region.The SMD of droplets measured at the outlet is less than 140μm,and the distribution is uniform.When 127Q_g162 m~3·h~(-1),the secondary breakup mode of droplets is bag breakup or pouch breakup.When 181Q_g216 m~3·h~(-1),the secondary breakup mode of droplets is shear breakup or catastrophic breakup.In order to ensure efficient atomization and mixing,the throat gas velocity of the tubular atomization mixer should be designed to be about 51 m·s~(-1)under the lowest operating flow rate.The pressure drop of the tubular atomization mixer increases linearly with the square of gas velocity,and the resistance coefficient is about 2.55 in single-phase flow condition and 2.73 in gas–liquid atomization condition.     

Genetic optimization of neural network and fuzzy logic for oil bubble point pressure modeling

Bubble point pressure is a critical pressure-volume-temperature (PVT) property of reservoir fluid, which plays an important role in almost all tasks involved in reservoir and production engineering. We developed two sophisticated models to estimate bubble point pressure from gas specific gravity, oil gravity, solution gas oil ratio, and reservoir temperature. Neural network and adaptive neuro-fuzzy inference system are powerful tools for extracting the underlying dependency of a set of input/output data. However, the mentioned tools are in danger of sticking in local minima. The present study went further by optimizing fuzzy logic and neural network models using the genetic algorithm in charge of eliminating the risk of being exposed to local minima. This strategy is capable of significantly improving the accuracy of both neural network and fuzzy logic models. The proposed methodology was successfully applied to a dataset of 153 PVT data points. Results showed that the genetic algorithm can serve the neural network and neurofuzzy models from local minima trapping, which might occur through back-propagation algorithm.     

内喷文氏管异常情况分析及改造

分析了某50kt／a硫铁矿制酸装置内喷文氏管出口气温超高、压力降上涨快的原因并采取相应改造措施，如改进喷头安装高度设计、优化工艺操作参数、加强设备和管道保温等。生产实践表明，必须加强内喷文氏管设计和操作，以保证设备稳定、高效地运行。     

文丘里管空化器内空泡动力学特性的数值模拟

研究了文丘里管空化发生器内空泡的成长、溃灭特性,根据基本的R-P空泡运动方程,考虑了液体粘性、表面张力和可压缩性等因素的影响,运用四阶Runge-Kutta法对空泡径向非线性运动方程进行求解,得到空泡径向演变过程以及溃灭压力的变化趋势.讨论了初始汽泡半径、入口压力和文丘里管的喉径比等因素对空泡演变过程的影响.结果表明,流体的可压缩性对空泡溃灭的影响最大;空化发生器结构参数以及操作参数均对空泡运动特性产生影响,从而影响空化强度.所得结果对空化流场中空化泡演变规律的研究以及水力空化发生器的设计具有指导意义.     

Gas holdup and energy dissipation in liquid‐gas ejectors

BACKGROUND: Ejectors have excellent mass transfer characteristics with energy efficiency and can be used in place of conventional countercurrent systems, namely, packed bed contactors as well as venturi scrubbers, cyclones and airlift pumps. Although a number of papers have been published in the recent past, none of them provides a theoretical basis for the prediction of gas phase holdup. In this work an attempt has been made to develop a theoretical basis for predicting gas phase holdup based on first principles using Nguyen and Spedding's distribution function (C_o) and initial value parameter (B). RESULTS: In the present work, measurements and correlations are reported for the gas holdup and energy dissipation in a liquid‐gas ejector. The holdup data have been correlated using the theoretical models proposed by Nguyen and Spedding, 26 with an estimated initial value parameter B and the distribution function C_o. The throat and diffuser loss coefficients were found to be constant up to a gas/liquid flow ratio of 1.6 and then it was found to be a function of area ratio, physical properties and gas holdup. CONCLUSIONS: The present proposed correlations for gas phase holdup and energy dissipation, E_mix, should be useful for the efficient design of co‐current ejectors for gas‐liquid contacting, in particular for the removal of CO₂ from natural gas, since the viscosity and surface tension ranges covered in the present study are essentially those encountered in amine–carbon dioxide systems. Copyright © 2008 Society of Chemical Industry     

文丘里管结构对高浓度煤粉流动特征及压差特性的影响

研究粉煤密相气力输送系统高压、高浓度煤粉通过不同节流比(0.44、0.55、0.7)、收缩角(2.5°、5°、9°)、扩张角(2.5°、8°、13°)、喉段长度(23d、43d、80d)的文丘里管的流动特征和压差特性。结果表明,不同结构参数的文丘里管的量纲1化压力分布趋势一致,但程度不一。其中节流比影响最为显著,并最直接地影响煤粉流经文丘里管的压差。节流比越小,总压差越大,扩张段压差显著增大。其他结构参数在各自的结构序列下主要改变文丘里管内压力分布,而对总压差改变不大。2.5°收缩角的收缩段压差最大,高浓度体系下5°和9°收缩角的收缩段压差差别不大。80d喉段长度的喉段压差最大。8°扩张角的扩张段压差最小。引入固相动量通量,获得本系统内煤粉流经文丘里管的压降经验方程,大部分实验点的计算偏差在30%以内,方程计算效果较好。     

Hydrodynamics of gas–solid flow in the circulating fluidized bed reactor for dry flue gas desulfurization

Process design and scale-up require a fundamental understanding of the hydrodynamics of gas–solid flow in the circulating fluidized bed flue gas desulfurization (CFB-FGD) reactor although the CFB system has been widely used in flue gas desulfurization and flue gas cleaning processes. The hydrodynamics in the CFB-FGD reactor model was investigated by pressure measurements and specially designed sampling probe based on three dimensionless groups for practicable similarity of industrial CFB-FGD process. The results show that the pressure drop in the venturi section is predominant as high as 60% of the total pressure drop and the total pressure drop significantly increases with the increasing external solid circulating rates at the same superficial gas velocity. Moreover, the measurements of radial solid mass fluxes show that the flow pattern in the CFB-FGD reactor is a typical core–annulus flow and this flow structure prevails until the top of the reactor. Reflux ratios are used to quantitatively evaluate the internal solid reflux in the reactor and the values in the low section of the reactor are much higher than those in the upper section.