Fractionation with condensation and evaporation in wetted-wall columns

A model is presented to describe the behavior of falling film fractionators with evaporation or condensation. Experimental measurements of vapor composition, vapor temperature and wall temperature profiles were made. Close agreement suggests that the model is applicable to both adiabatic and nonadiabatic conditions.     

处理多分散颗粒凝并和冷凝/蒸发问题的多重Monte Carlo算法

提出一个新的多重Monte Carlo (MMC) 算法来求解同时考虑凝并和冷凝/蒸发的通用动力学方程 (GDE),该算法基于时间驱动, 模拟过程中保持模拟颗粒数目不变和计算区域体积不变. 描述了时间步长确定方法, 同时处理凝并和冷凝/蒸发的方案. 针对常凝并核和常冷凝核, 常凝并核和线性冷凝核, 线性凝并核和线性冷凝核三种特殊工况, MMC算法模拟了颗粒尺度分布函数的时间演变, 与理论分析解进行了比较, 表明MMC算法能解决普通Monte Carlo算法的计算精度和计算代价不能协调的矛盾, 具有较小的计算代价和较高的计算精度, 能够适用于工程应用.     

凝并和冷凝/蒸发对颗粒尺度分布的影响

利用多重Monte Carlo算法对13种典型工况进行数值模拟,考察不同类型的凝并核和冷凝/蒸发核对多分散性颗粒尺度分布时间演变的影响。发现常凝并核要比线性和二次方凝并核对小颗粒的影响大一些、对大颗粒的影响小一些,线性和二次方凝并核对颗粒尺度分布的时间演变影响则取决于具体情况;常冷凝核要比线性冷凝核对小颗粒的影响大一些、对大颗粒的影响小一些;连续区布朗凝并核类似于常凝并核;扩散冷凝核对颗粒尺度分布的影响界于常冷凝核和线性冷凝核之间。     

降膜蒸发过程熵产分析

从热力学第二定律出发,将普适体系的熵产表达推广于降膜蒸发过程熵产分析并得到熵产计算式.引入单位熵产数并得到Reynolds数大于1450(c_pμ/λ)^-1.06(0.5-0.25ω)^-1情况下和Reynolds数之间的定量关系,据此揭示了降膜蒸发过程熵产随降膜管内液膜厚度减小先降低再增大的规律,对应存在最小熵产数.与φ30×2×6000传热管内磷酸降膜蒸发实验数据对比结果吻合良好,表明本文熵产计算式可以根据过程的热力参数表达降膜蒸发过程的熵产规律,对过程强化和提高热力学效率具有实际指导意义.     

反应冷凝和蒸发模型及其在反应精馏中的应用

为考察反应精馏过程中反应和分离间的耦合现象,建立了连续反应冷凝和反应蒸发模型。通过利用该模型对甲基叔戊基醚(TAME)合成反应精馏过程,考察了惰性组分的存在与不存在2种情况下,不同反应强度Da数对该过程的影响。指出了该反应精馏过程合理的塔结构形式、合适的反应强度范围、甲醇的过量程度以及产物组成状况。     

Multiple steady states in differential processes of open equilibrium evaporation and equilibrium condensation

The phenomenon of multiple steady states in open equilibrium evaporation and equilibrium condensation systems is considered.     

Light-emitting nanocomposite CdS-polymer electrospun fibres via in situ nanoparticle generation

We report on the simple, in situ generation of CdS nanocrystals inside electrospun polymer fibres by thermal decomposition of a cadmium thiolate precursor, leading to nanocomposite light-emitting fibres. The modifications induced in the precursor by the thermal decomposition are investigated by a morphological, structural and spectroscopic analysis of the resulting nanocomposite fibres. This approach allows us to overcome nanofabrication difficulties related to disfavoured micro- or nanofluidic molecular flow as given by the direct incorporation of particles in the electrospinning solution. This method therefore enables the synthesis of luminescent, CdS-based composite fibres with emission peaked in the visible range, suitable as building blocks for nanophotonic devices based on light-emitting nanomaterials.     

Reduction of the condensation/evaporation dynamics for atmospheric aerosols: Theoretical and numerical investigation of hybrid methods

The dynamical behaviour of atmospheric aerosols is characterized by a wide range of timescales, especially due to the fast growth of small particles through condensation/evaporation. The resulting models are particularly stiff and their numerical simulation still remains a challenge. Some techniques based on the assumption of condensation/evaporation equilibrium are usually advocated in order to circumvent these difficulties.The objective of this article is to investigate the different approaches on a theoretical basis. The appropriate framework is the theory of reduction for slow/fast models, for which many tools are already available. The application to aerosol modelling leads to the so-called hybrid methods. We also propose a hierarchy of reduced models and compare some numerical algorithms in a box model simulation for inorganic species.     

Difference in the rates of evaporation and condensation in the presence of an inert gas

On the basis of experimental data on the non-steady-state evaporation and the subsequent condensation of vapors of a substance on a flat cooled surface in the presence of an inert gas, the existence of the molecular and convective regimes of the condensation of vapors depending on the ratio of the molecular weights of the components of a gas-vapor mixture is found for the first time. It is shown that the kinetics of the evaporation-condensation processes differs: if the molecular weight of a vapor M _A is more than the molecular weight of an inert gas M _B, evaporation occurs in the molecular regime and condensation takes place in the convective regime; if M _A is less than M _B, the regimes of the processes change to the opposite ones. The results of experiments performed using ethyl acetate-air, ethanol-air, carbon tetrachloride-air, methanol-air, water-air, and water-helium systems are in satisfactory agreement with the results calculated by the proposed equation. Procedures for studying the dynamics of condensation and evaporation are described.     

蒸发/冷凝段长度比对脉动热管性能的影响

脉动热管是一种结构简单、传热性能突出的新型传热元件,由于运行过程涉及沸腾与冷凝及两相流动,传热及流动机理复杂,因此目前对其运行过程的相关数值模拟尚不成熟。本文采用VOF(volume of fluid)模型,考虑表面张力和壁面接触角的影响,采用数值模拟软件对单环路脉动热管的流动及传热特性进行了研究。数值模拟中,单环路脉动热管的充液率为40%～60%,热端加热功率为10～40W,探讨了热管蒸发段与冷凝段长度比对热管启动及换热性能的影响,并分析了脉动热管运行时流型特征。结果表明:随蒸发段和冷凝段长度比值增大,脉动热管启动时间缩短,且换热性能有一定提高;但在低充液率时,容易出现“干烧”现象。在低加热功率时,脉动热管的启动方式为温度突变式;而在高加热功率时,其启动方式为温度渐变式。此外,通过蒸发段的温度振荡特征可以确定脉动热管的启动时间。     

3200t/d预分解窑增产提效的技术改造措施

邓州中联水泥有限公司我公司3 200 t/d预分解窑投产后产质量低、能耗高;为此利用区域节能减排、协同停产的时间,通过对预分解窑和篦冷机进行扩产技术改造,实现了预分解窑优质、高产、低耗、低排放的良性循环,实际产量达3 900 t/d以上,熟料28 d抗压强度达60.2 MPa,标准煤耗为104.8 kg/t。     

Method of increasing yield of fluoropolymer powders in thermal destruction of polytetrafluoroethylene waste

A method was proposed that enables the development of an industrial technology for processing polytetrafluoroethylene by distilling it in NH₃-HF medium with a solid-phase product yield of more than 60%. The effect of the amount of ammonium hydrodifluoride introduced on the rate of the thermal destruction of polytetrafluoroethylene and the yield of fluororganic powder was studied.     

炼焦煤选煤厂提高选煤产率的新思路

结合古交某炼焦煤原煤煤质化验资料,提出对原煤进行初次低密度分选,分选完成后对低密度中煤进行超细磨矿,使煤与矸石充分解离,然后再采用絮团浮选的方式对其进行分选。在原有精煤灰分要求不变的情况下,将初次分选精煤与浮选精煤进行配比而得到最大精煤产量,达到提高精煤产率的目的。     

水泥余热发电100NB60凝结泵改造

我公司现有余热发电4.5 MW机组配套2台100NB60型凝结泵(凝结泵配备变频电动机),以前一直使用7306AC止推轴承,运行中经常出现因轴承温度升高而引起的轴承抱死现象,严重影响了机组的安全运行.本文针对水泥余热发电100NB60型凝结泵进行改造,并且提出相关建议.     

蒸发工段节能改造

对原蒸发装置中的废水排放工艺进行了改造，经改造后，年节水10万t以上，节省蒸汽千余t，经济效益显著。     

Growth of Zn2GeO4 thin film by thermal evaporation on ITO substrate for thermoelectric power generation applications

In this paper, we have reported the growth of Zn₂GeO₄ thin film and investigated its potential for thermoelectric power generation applications. Zn₂GeO₄ alloy thin film was grown on Indium coated glass substrate by the evaporation of Zn and Ge metals with constant oxygen gas flow rate of 100 sccm in tube furnace. The grown film was cut into pieces and annealed at various temperatures from 500° to 700°C with a step of 100?°C in a programmable furnace for one hour. The structure of as grown and annealed thin films was verified by XRD and Raman spectroscopy measurements. The XRD data evident that Zn₂GeO₄ alloy hexagonal structure along with GeO₂ and ZnO phases were observed at annealing temperatures 600 and 700?°C but below this temperature no alloy phase was detected by XRD and Raman Spectroscopy. To calculate the thermoelectric properties, temperature dependent Seebeck measurements were performed in the temperature range of 25–100?°C. It was observed that the value of Seebeck coefficient was increased from 91 to 847?μV/K as the annealing temperature increases from 500° to 700°C. This behavior was explained as; high temperature causes stress and cracks in the grown films which may induce electric and thermal discontinues at tips of cracks which cause high thermoelectric concentration. Scanning electron microscope images verified the development of cracks in the samples as annealing temperature increases. The behavior of Seebeck coefficient with the measurement temperature was also observed and explained in detail. The high value of Seebeck coefficient suggested that this material can be a potential candidate for thermoelectric power generation applications in near future.     

Kinetics of catalyzed acid/acid and acid/aldehyde condensation reactions to non-symmetric ketones

The kinetics and mechanism of acid and aldehyde condensations to produce non-symmetric ketones with CeO₂-based catalysts were studied using a combination of conventional and pulse microreactor tests. The effects of oxygen and water on the reactions were also studied.

Supported CeO₂ catalysts effectively catalyze the ketonization of acids at essentially complete conversion for extended periods, at weight hourly space velocities of 4–5. The optimal temperature range is 400–430 °C, depending on feed. Time on stream and number of regeneration cycles improved catalyst performance. Selectivities are improved by promotion with small amounts of potassium.

The acid/acid reaction to a typical methylketone proceeds roughly three times faster than the acid/aldehyde reaction, while the aldehyde/aldehyde initial reaction rate to desired methylketones is much slower; multiple aldol condensations predominate. When using acid/aldehyde feeds, water enhances ketone production, probably by supplying oxygen to the catalyst surface. While O₂ can fulfill a similar role, it also promotes combustion. Substitution of D₂O and CD₃COOH for water and acetic acid, respectively, led to kinetic isotope effects between 1.4 and 6.7, which is in the expected range for carboxylate decompositions.

Experiments at low conversion using CD₃COOH and either cyclopropanecarboxylic acid or its aldehyde showed that acetone and methylcyclopropylketone are formed preferentially as five D- and two D-atom isotopomers, respectively, for both acid/acid and acid/aldehyde feeds. This suggests the formation of a surface ketene intermediate, preferentially from acetic acid, which attacks a surface carboxylate to form the ketone, eliminating CO₂. The same conclusions could be drawn from ¹³C distributions in experiments using labeled acetic acid.     

降低蒸发系统中结盐的措施

分析了液碱蒸发装置结盐对蒸发传热系数、生产能力和蒸汽消耗的影响。通过减少盐进入量，降低蒸发装置结盐速率和优化操作来解决蒸发系统的结盐问题，达到了降低汽耗、提高效能的目的。     

Approaches to Enhance Precise CRISPR/Cas9-Mediated Genome Editing

Modification of the human genome has immense potential for preventing or treating disease. Modern genome editing techniques based on CRISPR/Cas9 show great promise for altering disease-relevant genes. The efficacy of precision editing at CRISPR/Cas9-induced double-strand breaks is dependent on the relative activities of nuclear DNA repair pathways, including the homology-directed repair and error-prone non-homologous end-joining pathways. The competition between multiple DNA repair pathways generates mosaic and/or therapeutically undesirable editing outcomes. Importantly, genetic models have validated key DNA repair pathways as druggable targets for increasing editing efficacy. In this review, we highlight approaches that can be used to achieve the desired genome modification, including the latest progress using small molecule modulators and engineered CRISPR/Cas proteins to enhance precision editing.