降膜式蒸发器在D-核糖浓缩中的应用

用肌苷水解法制备D-核糖时,得到的D-核糖水溶液需浓缩至水份低于2%的糖浆,才能进行结晶得到固体D-核糖产品。由于D-核糖在高温(50℃以上)条件下容易降解,所以浓缩过程要保证物料在高温状态的时间尽可能短,并尽可能降低物料接触热源介质的温度。我们选择了降膜式蒸发器作为浓缩设备,文章主要研究了如何合理地利用降膜式蒸发器来满足D-核糖浓缩的工艺要求。     

影响水平管降膜蒸发因素的实验研究

以去离子水作为水平管降膜蒸发实验介质,考察了喷淋密度对热通量、管外传热系数和总传热系数的影响与传热总温差对于管内、外传热系数和总传热系数的影响,并分析其产生影响的原因,得到了水平管内、外和总传热系数随各操作因素的变化规律。通过分析实验结果,在前人经验公式的基础上加以修正,获得了多因素共同作用下管外蒸发传热系数的实验关联式,为水平管降膜蒸发技术实际应用提供实验依据。     

Simulation of Orifice Flow Influenced by Lateral Flow in a Trough‐Type Liquid Distributor

A computational fluid dynamics (CFD) simulation is performed to investigate the influence of lateral flow on the orifice flow in a trough‐type liquid distributor. The discharge coefficients from the simulation are in good agreement with the experimental values, indicating that the CFD simulation is accurate in describing the outflow through orifices. The lateral flow near an orifice can change the velocity and pressure distributions of flow regions in front of this orifice, causing a decrease in the discharge coefficient. This phenomenon is supported by the theory of flow past a blunt body. An important implication derived from this finding is that the influence of lateral flow should be minimized in the design of a trough‐type liquid distributor, because the decrease in the discharge coefficient leads to non‐uniform outflow. The structure of a trough‐type liquid distributor is optimized to improve the liquid distribution performance by reducing the influence of lateral flow.     

多效降膜式蒸发器不同加料及出料方法的比较

以TNJM03-6200型三效降膜式蒸发器在木糖生产中的应用为例,对多效降膜式蒸发器不同加料及出料方法进行了比较,为优化工艺提供依据。     

降膜式蒸发器物料泵的确定选型及注意事项

以RNJM03-8000型降膜式蒸发器在奶粉生产中的应用为例,就泵的确定、选型及注意事项加以阐述.     

管外降膜湿润能力的实验研究

在不同进液流量、进液高度、进液孔径、管径和倾斜角下,用图像法测量了光滑圆管外壁液膜湿润长度,研究了各参数对液膜湿润能力的影响. 结果表明,随进液流量增大,液膜湿润能力先增大后稳定在一个固定值. 研究进液高度对湿润能力的影响时需考虑液膜的流型,流型为柱状流时,液膜进液高度对液膜湿润能力的影响较小;流型为柱状?片状流时,随进液高度增大,液膜湿润能力先减小后不变;流型为片状流时,液膜湿润能力达到饱和. 研究进液孔径对湿润能力的影响时需考虑液膜的流型,流型为柱状流时,液膜湿润能力随进液孔径增大先增大后减小,变化幅度较小;流型为柱状?片状流和片状流时,液膜湿润能力随进液孔径增大而减小. 一定流量下,管径越大,液膜湿润表面积越大,湿润能力越差. 受倾斜角度的影响,液膜湿润长度不再沿进液柱对称分布,湿润能力出现下强上弱的分布规律.     

降膜式蒸发器试车过程及注意事项

以RNJM03-2600型降膜式蒸发器在乳品工业中的应用为例,就设备试车过程、生产操作及有关注意事项进行阐述,指出降膜式蒸发器是在负压状态下工作的,蒸发系统在生产前的气密性、个效的状态参数、开车的顺序等,如果出现问题就会影响设备的使用效果。     

薄膜蒸发器挠性转子的研制

开发设计了一种适用于大型薄膜蒸发器的新型挠性转子,由于采用挠性转子,蒸发器筒体内表面不需加工,这为采用复合钢板制造简全了可能性,从而提高了薄膜蒸发器的传热效率,降低了制造成本,通过长期生产实践表明,转子结构设计合理,能够满足生产要求。     

大型降膜蒸发器物料的预热及应用

物料预热是降膜蒸发系统的重要组成部分。大型蒸发器的预热过程不能简单的按小型蒸发器的预热形式进行设计。随着物料处理量的增大，按常规预热形式预热物料往往达不到设定温度。     

竖直管降膜蒸发器流动与传热过程的数值模拟

针对竖直管降膜蒸发器的技术特点,在计算流体力学和传热学理论分析基础上,采用FLUENT软件,运用自定义函数(UDF)编写传质源项,对降膜蒸发器的加热管内液体沿壁面呈膜状下降流动并受热汽化过程进行了三维数值模拟研究,模拟采用Mixture两相流层流模型,Simple算法。模拟结果以3D形式表现了液体沿运动方向在管壁发展成膜的过程,并将模拟得到的液膜厚度与理论计算得到的液膜厚度进行了比较。模拟结果表明,竖直降膜蒸发器加热管具有液膜薄,均匀性好的特点,管表面容易形成柱状流,液膜厚度为1.0 mm。     

Characterization of Air‐Water Two‐Phase Vertical Flow by Using Electrical Resistance Imaging

The characterization of air‐water two‐phase vertical flow in a 12 m flow loop with 1.5 m of vertical section is studied by using electrical resistance tomography (ERT). By applying a fast data collection to a dual‐plane ERT sensor and an iterative image reconstruction algorithm, relevant information is gathered for implementation of flow characteristics, particularly for flow regime recognition. A cross‐correlation method is also used to interpret the velocity distribution of the gas phase on the cross section. The paper demonstrates that ERT can now be deployed routinely for velocity measurements and this capability will increase as faster measurement systems evolve.     

多效降膜式蒸发器蒸发温度高的原因

牛乳是热敏性物料,蒸发器蒸发温度高会对其中有益元素产生破坏,多效降膜式蒸发器蒸发温度高的主要原因是,物料与热量计算不守恒;设备漏气严重;冷凝器换热面积小或冷却水量不足冷却水温过高;冷凝器结垢严重;真空泵吸气量不足。     

基于fluent软件的布水器流态模拟

通过计算流体力学Fluent软件,对布水器流态进行了数值模拟。结果表明:在Re=19900时,绝对死区为0.0185,相对死区为0.0494m3,总死区比率高达43.3%;单纯采用操作优化或设计优化均可减小布水器死区,其优化幅度大致为38.0%左右,若采用操作和设计协同优化,可使死区降幅高达62.3%。设计布水器时,还应重点考虑近壁区布水孔的设计。     

Flow Structures of a Liquid Film Falling on Horizontal Tubes

Patterns of a liquid film falling across a vertical array of horizontal tubes change from droplet mode at low flow rates to liquid sheet at high flow rates. Between these limits, liquid columns form as a further stable flow pattern. The transition from one flow mode to another occurs via unstable structures consisting simultaneously of droplets and columns or of merging columns. The boundaries of the flow modes can be obtained from relationships expressing the flow rate as a function of physical properties, that is, the Reynolds number as a function of the Kapitza number. Correlations for the pattern boundaries recommended in the literature are compared with each other and found to be in acceptable agreement for practical purposes.     

填料塔液体分布器的设计(续三) 第四讲 堰槽式液体分布器的设计

介绍堰槽式液体分布器的结构、特性、适用范围、设计参数和设计方法,并给出了一个工业设计实例。     

薄膜蒸发器温度场及膜内给热系数的数值模拟

应用CFD软件CFX4.4建立了薄膜蒸发器内水及粘性料液的传热计算模型,获得了沿轴向及膜厚方向的液膜平均温度分布,计算了各参数下加热段液膜内给热系数a. 结果表明,进料量及搅拌转速对各料液液膜温度分布及膜内给热系数影响显著. 不同粘度料液在不同操作条件下均存在同一最佳进料量,此时圈形波内截面平均速度 达到最大值, 相应的膜内给热系数a也达到最大值. 高转速或最佳进料量下,纯物质水流动边界层与膜厚之比及温度边界层与膜厚之比均最小,流动边界层与温度边界层存在内在联系. 传递边界层厚度严重影响液膜内温度分布及给热系数. 本研究各工况下,粘性料液尚未形成明显的温度边界层.     

Generation of Two‐Phase Air‐Water Flow with Fine Microbubbles

Aiming at the development of a low‐cost technology for multipurpose water and surface treatment in the chemical industry and beyond, using microbubbles, a novel scheme of liquid‐gas interaction within a specially designed bubble generator was tested. Its efficiency for the production of microbubbles with a size distribution in the micron range is confirmed. The basic element of the device is a vortex chamber with water supply through tangential ducts, while the gas (air) is introduced in a highly turbulent swirling flow of water in radial direction through the orifice in the gas supply duct, located on the chamber axis. Bubble diameters, bubble velocities in the pipe flow and effect of the output pressure on the bubble size distribution were studied.     

Comparative Investigations of Non‐adiabatic Absorption in Film Flow and Bubble Flow

Comparative non‐adiabatic absorption experiments were carried out using the ammonia–water system under different two‐phase flow regimes. Because of the small thickness of the film, the falling film as a separated two‐phase flow shows an effective dynamic and transport behavior. The hydrodynamics and heat transfer modeling is sufficiently exact and the measurement of the interface temperature allows the discussion of the axial local partial resistance of the heat transfer in the falling film.     

Characteristics of a Comb Wiper for the Film Evaporator

In wiped‐film evaporators, wipers with comb‐wiping elements are often used. These elements are made of PTFE or electrocarbon and they bear on the concave evaporating area by the action of centrifugal force. This paper presents results of a study of the characteristics of such a wiper depending on the peripheral liquid load on the top of the evaporator, on the wiper peripheral speed and on the sense of wiper rotation. The shape of the residence‐time distribution curves (RTD curves) and the residence‐time values indicate the existence of three different hydrodynamic regimes for the film passage over the evaporating cylinder depending on operating conditions. Optimum distillation conditions are obtained in a regime with increased liquid retention resulting in a higher residence time. The augmented residence time is a positive factor which enables efficient evaporation to be carried out under gentle conditions at lower evaporator temperatures. It is possible to decrease or increase the passage of a liquid through the evaporator by a factor of two by changing the sense of the wiper's rotation. The obtained results show that there are interesting hydrodynamic conditions with intensive mixing on the evaporating cylinder at lower peripheral speeds. In addition, the longitudinal wave formation before the wiping element is minimized under these conditions.