FLOW IN AGITATED THIN FILM HORIZONTAL EVAPORATOR

Abstract

We made a theoretical analysis for an axial flow of a working liquid of low viscosity without concern for the thermal effects. Variables studied were rotational speed of wiping blades, volumetric flow rate and viscosity.

When the viscosity is low, theoretical values are in proper accord with experimental ones. As a result, we can say that the residence time and the effective area for heat transfer are able to be controlled (when the viscosity is low) by selecting the rotational speed.     

转鼓式生物反应器中液相体系的流动性能

采用粒子示踪测速法在18 L转鼓式生物反应器中考察了转速和挡板数、挡板类型和粘度对转鼓流场的影响. 结果表明,在低粘的自来水介质中,转速为4~12 r/min时,Y向平均分速度由0.029 m/s增加到0.053和0.064 m/s时,挡板重力提升能力不断增强,提高转鼓转速可促进全局混合. 直挡板数由4增加到8时,挡板提升能力增强32.5%,且能获得更均匀的流场分布;与自来水体系相比,高粘度8 g/L黄原胶溶液体系中流场分布更均匀,剪切更温和.     

Comparative analysis of residence and diffusion times in rotating bed used for biogas upgrading

Rotating bed can be used in desorption operation of biogas upgrading as a new technology. For enough time to desorb, it is important to study the relationship between the residence time of liquid in rotating bed and the material diffusion time of liquid droplet in desorption process. By theoretical deduction, the exponential relation between residence time and liquid flow rate and rotational speed and kinematic viscosity is obtained. By analyzing the solution of nonlinear partial differential equation, the time law of material diffusion in the droplet is obtained. Moreover, by comparing the residence and diffusion times, the diffusion time can be within or out of residence time range, which has a direct relationship to rotational speed and liquid flow. By experiment, the comparison between residence and diffusion times is more realistic when the rotational speed is higher.     

不同工艺下反应釜内PS/CO_2均相体系流变性能模拟

利用Fluent软件模拟不同工艺条件下反应釜内锥形混合元件所受的扭矩,依据锥板流变仪原理获得反应釜内PS/CO_2均相体的黏度,并分析熔体温度、CO_2质量浓度对均相体流变性能的影响。结果表明,当剪切速率一定时,升高熔体温度或CO_2质量浓度有助于降低均相体黏度;当熔体温度和CO_2质量浓度一定时,剪切速率越高,均相体黏度越低;且温度较低时,黏度随着CO_2浓度升高而下降的更剧烈。而均相体的黏度对于快速降压口模的压力降率有直接影响,对于如何获得更大的压力降率有指导作用。     

卧式双轴自清洁反应器粘性体系停留时间分布

在粘性体系中以茜素红为示踪剂,采用紫外光测试技术研究了卧式双轴自清洁反应器中的停留时间分布(RTD),利用返混模型对实验条件下的RTD及返混系数进行了模拟计算,得到了返混系数与雷诺数的关联式。结果表明,反应器的RTD受物料流速、搅拌速率及物料粘度等因素的影响,体系粘度增加返混系数减小;在实验范围内,基于返混模型的计算结果与实验结果基本相符。     

直接精馏法提取纤维素乙醇

采用直接精馏法研究了高固含量(质量分数)、高黏度的玉米秸秆发酵醪液的精馏工艺,设计了带搅拌桨的不锈钢筛板-填料精馏塔,确定了固含量为11.56%的发酵醪液的幂律模型本构方程,进而得到塔釜中发酵醪液的黏度和搅拌桨转速的关系。在进料量为2.7 L/h、进料体积分数为10%左右、进料温度为30℃、操作压力为常压的条件下,考察了进料位置、回流比、搅拌桨转速等操作条件对纤维素乙醇精馏的影响。实验结果表明:第27块塔板进料、操作回流比5.0、搅拌桨转速36 r/min为最佳操作条件,塔顶乙醇收率可达到99%以上。     

Rotating reverse osmosis for water recovery in space: influence of operational parameters on RO performance

Rotating reverse osmosis (RO), which is based on Taylor-Couette flow, offers a means to minimize flux decline due to concentration polarization and membrane fouling. However, the operating conditions play a significant role in determining the effectiveness of the system. In this study, the effect of operating conditions on system performance was explored using a theoretical model. Flux, rejection, recovery, and theoretical power consumption were calculated for a wide variety of operating parameters including transmembrane pressure, rotational speed, and concentrate flow rate. Flux and rejection increase with increasing transmembrane pressure and rotational speed. Operating in the vortical flow regime enhances the filtration performance. Higher concentrate flow increases flux, but decreases recovery. The power consumption for rotating RO is similar to that for conventional RO except at very high rotational speeds.     

Characterisation of rendering mortars by squeeze-flow and rotational rheometry

This paper reports the first experimental comparison between squeeze-flow at controlled displacement rate and rotational shear at controlled speed for evaluating the rheological behaviour of mortars. Several Brazilian and European rendering products showed a wide range of workability behaviour in both testing modes. The flow curves and hysteresis effects during the shear cycle varied significantly, since the mortar's composition affects structural breakdown, interfacial slip and phase segregation. The latter plays a critical role during squeeze-flow and is the main reason for the higher loads required to deform the samples at lower rates. A gravimetric-based methodology was developed to assess phase segregation induced by rotational tests. Encouraging agreement between the methods was observed, with yield stress in the structured (unsheared) state showing a good linear correlation. For some mortars showing low segregation it was possible to compare shear viscosity and extensional viscosity and Trouton ratios between 20 and 40 were obtained.     

基于颗粒轨迹分析的分级机切割粒径计算

为研究超细分级机的切割粒径,采用计算流体力学技术对分级机气固两相流进行了数值模拟。计算中气相采用RNG k-ε湍流模型,颗粒相采用随机轨道模型。通过分析颗粒轨迹与切割粒径的关系,揭示了颗粒在分级机内运动的物理机制;通过分析切割粒径随转子转速、风量、喂料浓度和物料密度的变化规律,阐述了各参数对切割粒径的影响。结果表明：切割粒径的理论推算中,忽略叶片厚度的影响将导致计算值偏小;低转速（450 r/min,600 r/min）时,受局部涡流的影响,切割粒径模拟值与理论计算值相差较大,最大误差为13.58%;与风量相比,转速对切割粒径的影响更为显著。模拟结果与理论计算值吻合较好,为求取分级机的切割粒径提供了一种新方法。     

最大叶片式桨在假塑性流体中的搅拌流场模拟

为研究最大叶片式桨在高黏假塑性流体中的搅拌流动行为,以黄原胶溶液为研究体系,采用计算流体力学方法重点研究了釜内流体的功耗特性、速率分布、剪切速率、表观黏度分布和总体流动状况。结果表明:最大叶片式桨具有与大多数径流桨相似的"双循环"流型结构,且预测的功耗特性与实验数据一致性良好。最大叶片式桨适用于高黏假塑性流体的混合,而对于高黏牛顿流体的混合则效果不佳。釜内的剪切速率分布较宽泛,且受转速影响较大。转速可作为该桨改善黄原胶体系混合效率的重要参数之一。     

二氧化碳压缩机降速节能问题的探讨

介绍二氧化碳压缩机的流程及主要性能参数，通过理论计算和初步实验探讨降低机组转速的可能性。结果表明，在稳定机组运行的前提下，可适当降低转速，有利于优化控制和节能降耗。     

Helical flow of curing highly viscous liquids

For profile extrusion of rubber, a shear head is frequently placed at the outlet of the extruder. In the shear head, the rubber compound is heated to its cure temperature by means of internal friction between two coaxially rotating cylinders (annulus). The aim of this examination is to find suitable operating parameters for all rubber compounds. The highest possible temperatures and an even cure profile are the characteristics of suitable operations. The degree of cure should be as close as possible to the maximum cure permitted. For examination of the processes in the annulus, a coupled system of differential equations is set up and solved numerically. The cure profiles established along the annulus are of special interest. The effects of the geometry, the rotational speed of the inner cylinder, the volumetric flow, the operating temperatures, and the viscosity as a function of the shear rate and the temperature are examined. The results of the calculations show that the viscosity, which increases with increasing cure, has a strong effect on the velocity and dissipation profiles. The results of the experimental investigations on a shear head coincide well with theoretical prediction.     

超重力旋转床微米级粉尘脱除的试验研究

用超细滑石粉模拟工业微米级粉尘,通过试验研究了超重力平面丝网旋转床的除尘特性。考察了旋转床在实验室不同的气体流量、液体流量、转速和平面丝网层数条件下的除尘效果,试验结果表明,气体流量600m~3/h、液体流量大于0.6 m~3/h、转速1400 r/min、轴向放置3层平面丝网时,除尘总效率大于97%,设备压力降不超过490 Pa。该旋转床具有高效除尘和低阻性能,若在硫酸净化系统中使用,预期可获得节能与高效净化效果。     

Droplet break-up by in-line Silverson rotor–stator mixer

Silverson high shear in-line rotor–stator mixers are widely applied in industry for the manufacture of emulsion-based products but the current understanding of droplet breakage and coalescence in these devices is limited. The aim of this paper is to increase the understanding of droplet break-up mechanisms and to identify appropriate literature correlations for in-line rotor–stator mixers. Silicone oils with viscosities ranging from 9.4 to 969 mPa s were emulsified with surfactant in an in-line Silverson at rotor speeds up to 11,000 rpm and flow rates up to 5 tonnes/h. The effect of rotor speed, flow rate, dispersed phase fraction up to 50 wt%, inlet drop size and viscosity ratio on droplet size was investigated. It was found that rotor speed and dispersed phase viscosity have a significant effect on the droplet size, while flow rate, inlet droplet size, viscosity ratio and dispersed phase volume have a lesser effect. The results indicate that low viscosity droplets are broken by turbulent inertial stresses, while droplets smaller than the Kolmogorov length scale are broken by a combination of inertial and viscous stresses. It also appears that the weak dependence of drop size on flow rate enables the energy efficiency of an in-line high shear Silverson to be significantly improved by operating at as high a flow rate as possible.     

Study of bubble induced flow structure using PIV

An experimental investigation of the flow structure induced by a chain of gas bubbles was carried out in a rectangular bubble column using particle image velocimetry (PIV). It is observed that the bubble rising trajectory changes from one dimension to three dimension as liquid viscosity reduces. The variation of bubble rising trajectory associates with the alternation of bubble motions—with or without oscillatory and rotational motion depending the bubble rising trajectory is 3-D or 1-D. The different behaviors of gas bubbles introduce various instantaneous and averaged liquid flow structures. In general, complex fluid velocity fields present in liquid system of low viscosity where free vortex, cross flow, and irregular circular flow can be observed. The liquid pseudo-turbulence measured in terms of turbulence intensity and Reynolds stress is more intense in liquid of low viscosity. The turbulence is also enhanced by the frequency of bubble formation.     

Effect of viscosity on liquid curtain stability

The effect of viscosity on liquid curtain stability was explored by high‐speed visualization. Measurements of the velocity within the curtain revealed the presence of a viscous boundary layer along the edge guides. The critical condition at the onset of curtain breakup was determined by identifying the flow rate below which the curtain broke for two different edge guide geometries: parallel and convergent. Curtain breakup was initiated by the expansion of a hole within the curtain. For low viscosity liquid, the measured hole retraction speed is independent of the viscosity and equal to the Taylor‐Culick speed. For high viscosity liquids, the retraction speed is lower than the Taylor‐Culick speed due to viscous forces that resist the flow. The results also show the effect of liquid viscosity on the curtain stability is a strong function of the edge guide design. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1448–1457, 2018     

ATMOSPHERIC CONTACT DRYING OF GRANULAR BEDS WETTED WITH A BINARY MIXTURE

When regarding the atmospheric contact drying of granular beds wetted with a liquid mixture, both the drying rate and the selectivity of the process, i.e. the change of moisture composition, are of interest. The batch drying of a free flowing ceramic substance, wetted with a 2-propanol-water mixture, is investigated in a rotary dryer with heated wall and air flow.

The theoretical analysis is based on physical models for heat and mass transfer, moisture migration and particle transport, which are presented in examples.

The experimental and theoretical results show that higher selectivities can be achieved by reducing the particle size because of the lower liquid-phase mass-transfer resistance. An increase of the rotational speed leads to a higher drying rate with slightly decreased selectivity if the particles are sufficiently small, since contact heat transfer is enhanced.     

Quantitative Analysis of Mixer‐Type Rheometers using the Couette Analogy

A procedure based on a Couette analogy, to quantitatively analyze torque/rotor speed data in order to extract viscosity/shear‐rate curves using non‐conventional geometries is presented. It is first validated using a relatively simple geometry for which the equivalent internal radius used in the analogy can be analytically obtained. The results showed that the equivalent internal radius depends only slightly on the nature of the fluid and that there is an optimal radial position r* in the analog Couette gap where the calculations can be easily performed for computing the viscosity/shear‐rate data from torque/rotational speed data. The experimental results with complex geometries and complex fluids are found to coincide, within experimental errors, with those obtained using standard geometries over a wide range of shear rates. The approach is also found to be very useful to evaluate shear‐rate and viscosity data in Couette viscometers when large gaps are used with non‐Newtonian fluids.     

三螺杆挤出机螺纹元件流场分析

基于三角形排列的三螺杆挤出机的研究开发实践,对螺纹元件所形成的流场,特有的三个啮合区和中心区流场进行了模拟研究。通过对流速、流向、剪切速率、剪切黏度等挤出特性的剖析,说明这种三螺杆挤出机具有较强的输送能力;三个啮合区较其他区域有高的速度梯度、剪切速率;中心区存在瞬态环流和回流。在计算条件下,中心区的物料中的95％会在5 s内流出中心区,其余物料在中心区的停留时间不会超过100 s。     

Performance of a rotating zigzag bed—A new HIGEE

As a new kind of rotating equipment, rotating zigzag bed (RZB) is structurally unique and has many superior features. The RZB is characterized by a rotor coaxially combining a rotating disc with a stationary disk. Compared with a conventional rotating packed bed (RPB), the RZB can function without liquid distributors, eliminate one dynamic-seal, and easily accommodate and accomplish intermediate feeds in continuous distillation processes. The RZB also effectively increases the contact time of gas and liquid phases and thus, enhances the mass transfer capacity. In this work, the principles of the RZB are presented. The hydraulic and mass transfer performance of the RZB was investigated. Experimental results showed that the pressure drop of the RZB increases with the increase of the rotational speed and the gas flow rate, but decreases with the increase of the liquid flow rate. A semi-empirical equation was proposed to correlate the pressure drop data with good agreement. The mass transfer efficiency of the RZB decreases with the increase of the reflux rate at lower reflux rate, but levels off at higher reflux rate. The number of theoretical plates of the RZB increases with the increase of rotational speed of the rotor. However, at a higher rotational speed, this trend is not obvious. In addition, some considerations for further work are discussed.