Investigations on the Droplet Entrainment in a Forced Circulation Flash Evaporator

This contribution presents results from entrainment measurements in a forced circulation flash evaporator which was designed to systematically investigate the droplet entrainment under real evaporating conditions. Operating pressures in a range of 100 to 800 mbar(a) and temperature differences between 5 and 55 K were conducted. Gas load factors up to f_G = 4.0 Pa^0.5 were achieved with glycerol-water and water as evaporating liquids. A conductivity measurement was used to determine the absolute entrained liquid and entrainment ratios. The results show an exponential behavior between entrainment, gas load factor, and heat flux due to superimposing effects. Investigation on the pressure drop across the orifice plate showed no influence for operation at gas load factors of f_G < 2.5 Pa^0.5.     

Quantification of Entrainment Using an Optical Inline Probe

In distillation and absorption processes, entrainment above trays or packings reduces stage and column efficiency. A modified version of the optical multimode online probe enables a seminal insight and, thus, quantification of entrained droplets on various axial and radial positions. A purging mechanism inhibits precipitation of droplets on the front lenses, while telecentric optics and illumination provide distance‐independent and precise imaging of entrained droplets between two valve trays. Experiments were performed in a DN 450 cold flow (air‐water) test rig. The results were compared with noninvasive phase Doppler anemometry data.     

Qualification of Image-Based Measurement Systems for Characterization of Sprays

Image-based measurement techniques become increasingly popular and expedite digitalization in chemical engineering. This article demonstrates their potential by testing two inline probes, namely modified optical multimode online probe (OMOP) and process microscope. Validations are performed with static monodisperse standards (9.2 µm to 406 µm) and fast-moving droplets (68.6 µm to 860.7 µm; 24.5 m s⁻¹ to 11 m s⁻¹). Screening of a lithography attests both probes great distortion-free image quality. A 1951 USAF chart attests a low optical resolution of 8 µm or 7 µm with respect to the OMOP or process microscope, respectively. The modified OMOP and process microscope reaches accuracies of 7.6 % or 5.9 % for particles and 8.2 % or 6.8 % for droplets.     

Predicting Droplet Size Distribution by Image Processing Technique for an Air Blast Atomizer

An image processing technique was used to predict the size distribution of the high speed, fine droplets at downstream of an air blast atomizer. The spray visualization setup consisted of UV lamps as light source, a stroboscope for slowing down the droplet motion, and a digital camera to capture the droplet images. The experiments were carried out at different liquid flow rates with various nozzle diameters. Two key unknown parameters (spray half angle and dispersion angle) of the air blast atomizer model in Fluent were obtained from these experiments. Using the obtained parameters and other structural parameters, the spray modeling was performed, and the Rosin–Rammler distribution was obtained and compared with those obtained from image processing technique through a diagnostic matrix. Regarding the kappa value, the agreement between predictions of the Fluent model and the image processing technique was moderate.     

Simulation of a forward feed multiple effect desalination plant with vertical tube evaporators

In recent years, vertical tube falling film evaporators have been widely used in desalination industries. In this paper mathematical modeling of a multiple effect evaporators (MEE) system has been carried out for brackish water desalination. The system includes a set of forward feed vertical tube evaporators with thermal vapor compression (TVC) and a condenser. Modeling has led to calculation of several parameters such as overall heat transfer coefficients, entrainment ratio and recovery of the process which is restricted by scale formation. A scaling prediction chemical model has been employed to calculate the allowable rate of recovery for prevention of scale formation. Physical properties of streams have been assumed as functions of temperature and salinity. A code has been developed for simulation of the process based on mass and energy balance equations. Results showed maximum allowable recovery of 74% for the treated brackish water sample with total dissolved solid (TDS) of 14,761 ppm is achievable. Dealing with mentioned sample under specified set of conditions, it was concluded that changing the number of effects from 3 to 8, enhances gained output ratio (GOR) value from 3.8 to 7.5. However, specific heat transfer surface is increased from 215 to 1052.     

强制循环蒸发器内流体停留时间分布测试分析

分析强制循环蒸发器内流体停留时间分布测试中示踪剂循环对响应曲线的影响，建立了循环条件下所测定的循环响应曲线Ｃｒ（ｔ）与蒸发器和循环管内流体停留时间密度函数Ｅ１（ｔ）、Ｅ２（ｔ）之间的基本关系，并以此处理循环条件下直接引入示踪剂的实验测试数据，获得了满意的停留时间分布曲线。     

CFD Evaluation of Droplet Drying Models in a Spray Dryer Fitted with a Rotary Atomizer

Computational fluid dynamics (CFD) modeling of spray dryers requires a simple but sufficiently realistic drying model. This work evaluates two such models that are currently in discussion; reaction engineering approach (REA) and characteristic drying curve (CDC). Two versions of the CDC, linear and convex, drop in drying rate were included. Simulation results were compared to the overall outlet conditions obtained from our pilot-scale experiments. The REA and CDC with a linear drop in drying rate predicted the outlet conditions reasonably well. This is contrary to the kinetics determined previously. Analysis shows that the models exhibit different responses to changes in the initial feed moisture content. Utilizing different models did not result in significantly different particle trajectories. This is due to the low relaxation time of the particles. Despite the slight differences in the drying curves, both models predicted similar particle rigidity depositing the wall. For the first time in a CFD simulation, the REA model was extended to calculate the particle surface moisture, which showed promising results for wet particles. Room for improvement was identified when applying this concept for relatively dry particles.     

Digital Image Processing Technique to Investigate the Hydrodynamics of an Airlift Reactor with Double Downcomer

Digital image processing, an innovative cost‐effective technique, was employed to investigate the hydrodynamics of a rectangular internal loop airlift reactor with double downcomer. The whole reactor was divided into two downcomers and a riser by means of two vertical blades to achieve a new geometry. Air and water served as gas and liquid media. Experimental measurements were performed by visualizing the concentration of a colored tracer by a digital camera. The captured successive images at specified time intervals were analyzed by the ImageJ software to turn images into quantifiable data. For four reactor geometries, the residence time distribution curves in individual sections and the liquid mixing performance were determined by this noninvasive method. The speed of this technique to capture real‐time data of flow patterns may be one of the most important concerns for imaging multiphase flows in process industries.     

炼铜闪速炉升温膨胀数据的测定及相关问题的分析

介绍了炼铜闪速炉改造后升温过程中炉体膨胀数据的测定方法,针对一些测定异常的炉体膨胀数据进行分析并提出改进意见。     

Dairy Milk Particles Made with a Mono-Disperse Droplet Spray Dryer (MDDSD) Investigated for the Effect of Fat

Mono-disperse droplet generation and subsequent drying in a spray-drying chamber, i.e., mono-disperse droplet spray dryer (MDDSD), provides a better-defined “flight experience” for liquid droplets. The related particle formation can be investigated more easily than that in the usual poly-disperse droplet spray dryer (PDDSD). Previously, skim milk, which is of high protein and high lactose content and is one of the two main dairy fluids that are processed into powder form for consumer markets, was subjected to this kind of investigation in Australia. Here, whole milk, which is the other main dairy fluid, has been spray-dried in a MDDSD set-up at Xiamen University (China). Because the initial droplet size is uniform, measurable, and the particle morphology after drying is consistent, it was possible to investigate the initial solids content effect upon shrinkage and inlet air temperature effect upon shrinkage. In contrast to what had been found for skim milk particles, the formation of the fat-containing (whole milk) particles does not follow the perfect shrinkage model as the skim milk does. This work has improved our quantitative understanding of the whole milk drying process. A fundamental analysis invoked with a modified one-dimensional modeling of spray drying has been given that has shown some further insight about the process.     

Particle Size Measurement of Metallic Iron in Reduced Materials Based on Optical Image Analysis

The size of metallic iron particles in coal‐based reduced materials was measured by optical image analysis in three different reduced samples. The obtained data were analyzed by frequency and cumulative distribution. The results reveal that optical image analysis successfully measured the particle size of metallic iron in the reduced samples. The frequency distribution curves or cumulative passing percentage of metallic iron particles exhibit almost the same trend with respect to particle size. The quality of curve fitting indicates that the exponential decay function and Rosin‐Rammler equation represent well experimental data on frequency distribution and cumulative passing percentage, respectively.     

Investigations on the role of surfactants in mechanical emulsification using a high-pressure homogenizer with an orifice valve

The objective of the research work presented in this paper is to elucidate the role of surfactants during mechanical emulsification. To find out whether droplet disruption or stabilization, or both, are influenced by emulsifiers, the time for disruption and stabilization were calculated approximately. Recent developments in the institute have shown that elongational flow is the most efficient flow regime to produce emulsions with submicron droplets. Experiments, therefore, were carried out using a high-pressure homogenizer with an orifice valve. To illustrate the emulsification process the process was videotaped using a high-speed camera. Calculations for the experimental conditions investigated show that a large number of subsequent disruption steps can take place in the elongational flow. The surfactant is capable of adsorbing at newly formed droplets between subsequent disruption steps. Thus, the total disruption process can be facilitated by surfactants. Further, comparing adsorption time and residence time in the elongational flow shows that stabilization of newly formed droplets in the elongational flow is possible. The emulsification experiments show that between subsequent disruption steps the surface load is not balanced over the droplet’s surface. The results indicate that the adsorption process is governed by adsorption from the subsurface to the surface. The pictures obtained by videotaping support the results of calculations and emulsification experiments: droplet deformation with and without surfactant is not significantly different. If stabilization is poor, droplets recoalesce and the disruption result is reversed.     

Energy Analysis and Air Entrainment in an Ejector Induced Downflow Bubble Column with Non‐Newtonian Motive Fluid

In an ejector induced downflow bubble column energy supplied as a high velocity liquid jet is utilized in different sections of the ejector‐contactor system, which leads to air entrainment at the secondary entrance of the ejector. The energy losses in the different sections, viz. ejector, mixing zone and gas‐liquid bubbly flow zone have been evaluated theoretically. Experimental results show that the total energy losses calculated on the basis of theoretical expression are almost the same as energy supplied by the liquid jet. A simple correlation was developed for the air entrainment rate in terms of operating and design parameters of the system.     

乙酰丙酮法测定水中甲醛含量的测量结果不确定度分析

对乙酰丙酮法测定环境水样中甲醛含量的测量结果的不确定度进行了全面评估;系统分析了影响分析方法测定结果不确定度的各种因素,并计算出各因素所对应的相对不确定度分量;对比构成总的合成相对不确定度的各个分量,可知方法测量结果的不确定度主要来源是标准曲线的绘制过程;最后通过计算得出了分析方法的合成不确定度和扩展不确定度.     

环境分析样品前处理新技术及其应用研究进展

环境分析样品前处理是环境分析化学的重要组成部分,是当代环境分析的一个前沿课题.文章综述了前处理方法在环境分析中的意义,环境分析样品前处理新技术的原理、特点、应用和研究进展.     

工学结合模式下中职《工业分析技术》课程改革探索与实践

文章结合《工业分析技术》课程,具体讨论了工学结合在该课程中进行的一些改革和探索。通过改革优化了教学内容,改进了教学方法,改变了考核方式,从而调动学生学习的主动性,培养了学生的综合职业能力和创新能力。     

A novel whitening test method of a sulfur-cured EPDM composite filled with carbon black in calcium cation solution

A simple and efficient whitening test method of a carbon black-filled sulfur-cured EPDM composite by formation of calcium stearate was established using Ca²⁺ solution and convenient analytical techniques. The sample was aged in 0.1 M CaCl₂ solution at 30–90 °C for 1 and 3 days. ATR-FTIR spectra of the aged sample surfaces displayed unique calcium stearate peaks. Level of the whitening of a rubber article can be determined by analysis of the cross section of the aged sample using an image analyzer and by analysis of calcium stearate on the aged sample surface using an ATR-FTIR.     

Analysis of Ozone in Aqueous Solutions Using A Modified Iodometric Technique with as (III)

A modified iodometric procedure using an absorbing solution of 2% NBKI with a known amount of As(III) is described for 10 ml aqueous samples. Ozone contents from 0.5 to 65 mg O3/I were determined. High ozone concentrations can also be measured for generator calibration. This method gives results which are not significantly different than a boric acid method but are for a modified standard methods procedure. Volatility of iodine has been completely eliminated. Stabilized samples do not make the time between sampling and final titration critical.     

新型干法预分解磷石膏制硫酸联产水泥可行性分析

磷石膏是湿法磷酸生产时排放的固体废弃物,磷石膏制硫酸联产水泥技术一直为人们高度重视,但这一技术至今尚未有实质的突破.近年来许多学者提出了利用水泥新型干法技术来实现磷石膏预分解制硫酸联产水泥的新工艺.为此本文结合水泥新型于法预热分解窑的热工特点,以及磷石膏的热分析,研究了在该工艺条件下,磷石膏的分解温度与正常预热分解炉的适应性,磷石膏分解效率及窑系统粘结堵塞等特性.结果表明,采用新型干法水泥技术分解磷石膏制硫酸联产水泥是十分困难的.