Measurement of 2-ethyl-1-hexanol emitted from flooring materials and adhesives

It has been reported that 2-ethyl-1-hexanol (2E1H) was emitted through hydrolysis between di-2-ethylhexyl phthalate used as plasticizer in flooring material and moisture generated from a strongly alkaline material such as concrete slab. The purpose of this study was to clarify the relationship between diffusion of 2E1H in flooring material and 2E1H emission rate from floor surface. In this study, we measured 2E1H emitted from floor paper, poly(vinyl chloride) (PVC) tile, cushion floor and carpet for 200,?days and effective diffusion coefficients for 2E1H in various flooring materials were measured. Effective diffusion coefficients of 2E1H for cushion floor and PVC tile were 115?×?10^?9 and 7.8?×?10^?9 m²/s, respectively. Emission rate of 2E1H emitted from flooring material significantly depends on the kind and shape of flooring materials and was influenced by the effective diffusion coefficient for 2E1H of flooring material. Emission rates of 2E1H from floor surface varied with the amount of 2E1H and resin present in the adhesive. When carpet was attached to the flooring material with high water content using adhesive, emission of 2E1H significantly increased. The results show that primary and secondary emissions of 2E1H from the adhesive influence the emission rate of 2E1H for flooring material.     

建材VOC散发过程模拟与传质参数测定新方法

建材中挥发性有机化合物(VOC)的散发是一个复杂传质过程。为准确把握传质特性,首先建立了一套描述干建材散发行为的显性完全解析模型,适用于模拟对人体最不利的无换气情况;代入有关文献中的传质参数预测了环境舱浓度,与文献中对应的实验数据及数值算法预测值吻合良好。然后基于对模型的分析提出一套简便快捷的实验方法,能够利用不同VOC背景值下干建材在密闭舱中散发的平衡浓度或逐时浓度,求取预测散发过程的4个重要的传质参数:可散发浓度C₀、扩散系数D、分配系数K和对流传质系数h_m;实验部分测算了两类密度板中甲醛散发的C₀、D、K、h_m,代入数值算法预测了密闭舱和直流舱的环境舱浓度,与实验数据吻合良好。该套模型和测定方法能够应用于建材散发的模拟研究。     

Effect of surfactants on liquid-side mass transfer coefficients

In the present paper, the effect of liquid properties (surfactants) on bubble generation phenomenon, interfacial area and liquid-side mass transfer coefficient was investigated. The measurements of surface tension (static and dynamic methods), of critical micelle concentration (CMC) and of characteristic adsorption parameters such as the surface coverage ratio at equilibrium (s_e) were performed to understand the effects of surfactants on the mass transfer efficiency. Tap water and aqueous solutions with surfactants (cationic and anionic) were used as liquid phases and an elastic membrane with a single orifice as gas sparger. The bubbles were generated into a small-scale bubble column. The local liquid-side mass transfer coefficient (k_L) was obtained from the volumetric mass transfer coefficient (k_La) and the interfacial area (a) was deduced from the bubble diameter (D_B), the bubble frequency (f_B) and the terminal bubble rising velocity (U_B). Only the dynamic bubble regime was considered in this work (Re_OR=150-1000 and We=0.002-4).This study has clearly shown that the presence of surfactants affects the bubble generation phenomenon and thus the interfacial area (a) and the different mass transfer parameters, such as the volumetric mass transfer coefficient (k_La) and the liquid-side mass transfer coefficient (k_L). Whatever the operating conditions, the new k_La determination method has provided good accuracy without assuming that the liquid phase is perfectly mixed as in the classical method. The surface coverage ratio (s_e) proves to be crucial for predicting the changes of k_L in aqueous solutions with surfactants.     

建筑外表面对流传质系数的测量方法

建筑外表面对流传质系数是围护结构热湿耦合计算和建筑能耗模拟中的重要参数。为直接准确得到该参数,提出了建筑物壁面对流传质系数的测量方法,该方法通过测量萘试件的质量通量和表面温度,即可计算得到壁面传质系数。为验证该方法的准确性及可靠性,在风洞内设置6组不同风速工况,分别采用了萘升华法与传统热平衡法进行对比。结果表明：随风速的增加,萘试件表面温度随之降低,而对流传质系数逐渐增加。两种方法测试结果接近,二者所得对流传质系数相差在10%以内,不同风速条件下平均偏差小于5%,认为该测量方法可行。该研究可为室外真实条件下建筑外表面对流传质系数提供测试方法指导,对热湿耦合计算和墙体蒸发换热的研究也具有重要意义。     

Determination of external mass transfer coefficients in dynamic sorption (DVS) measurements

A sorption balance is an instrument used to measure vapor uptake in a sample at controlled temperature and relative humidity. It is most commonly used to determine equilibrium values (sorption isotherms), but is also used for kinetic measurements of transport coefficients. Such measurements can be affected by the external mass transfer resistance in the gas phase around the sample. This paper presents a method to determine the external mass transfer coefficient for a given flow geometry using a water saturated sample, including corrections for temperature changes from evaporative cooling, which is found to have considerable effect on the calculated constant.     

On the use of internal mass transfer coefficients in modeling of diffusion and reaction in catalytic monoliths

We utilize the recently developed concept of internal or intraphase mass transfer coefficient to simplify the problem of diffusion and reaction in more than one spatial dimension for a washcoated monolith of arbitrary shape. We determine the dependence of the dimensionless internal mass transfer coefficient (Sh_i) on washcoat and channel geometric shapes, reaction kinetics, catalyst loading and activity profile. It is also reasoned that the concept of intraphase transfer coefficient is more useful and fundamental than the classical effectiveness factor concept. The intraphase transfer coefficient can be combined with the traditional external mass transfer coefficient (Sh_e) to obtain an overall mass transfer coefficient (Sh_app) which is an experimentally measurable quantity depending on various geometric and transport properties as well as kinetics. We present examples demonstrating the use of Sh_app in obtaining accurate macro-scale low-dimensional models of catalytic reactors by solving the full 3-D convection-diffusion-reaction problem for a washcoated monolith and comparing the solution with that of the simplified model using the internal mass transfer coefficient concept.     

气液固微型流化床的气液传质系数

气液固微型流化床兼具微流控系统和宏观流化床的优点,具有潜在的工业应用价值,但是,其应用基础研究十分缺乏。采用床径为1.6、2.0、2.4 mm的微型流化床,平均粒径为160、190、220 μm的玻璃珠,以NaOH水溶液吸收CO₂气体为气液传质研究物系,在三相流动研究的基础上,考察了表观气速、表观液速、床径、粒径等对三相微型流化床气液体积传质系数的影响。结果表明：给定其他条件,增加表观气速和表观液速,均使气液体积传质系数增大;表观气速主要改变气含率和气液相界面积,而表观液速主要改变液相传质系数;床径减小,气液相界面积和气液体积传质系数都有所增加;在气液两相微型鼓泡塔中加入固体颗粒,形成三相分散鼓泡流型,当其固含率在0.15~0.30范围内,可显著增强气液传质,其气液体积传质系数是气液微鼓泡塔的1.1~1.5倍;与宏观流化床相比,相同条件下微型床的相界面积为它的5~10倍,是微型流化床具有更大体积传质系数的主要影响因素。     

气液固微型流化床的气液传质系数

气液固微型流化床兼具微流控系统和宏观流化床的优点,具有潜在的工业应用价值,但是,其应用基础研究十分缺乏。采用床径为1.6、2.0、2.4 mm的微型流化床,平均粒径为160、190、220 μm的玻璃珠,以NaOH水溶液吸收CO₂气体为气液传质研究物系,在三相流动研究的基础上,考察了表观气速、表观液速、床径、粒径等对三相微型流化床气液体积传质系数的影响。结果表明：给定其他条件,增加表观气速和表观液速,均使气液体积传质系数增大;表观气速主要改变气含率和气液相界面积,而表观液速主要改变液相传质系数;床径减小,气液相界面积和气液体积传质系数都有所增加;在气液两相微型鼓泡塔中加入固体颗粒,形成三相分散鼓泡流型,当其固含率在0.15~0.30范围内,可显著增强气液传质,其气液体积传质系数是气液微鼓泡塔的1.1~1.5倍;与宏观流化床相比,相同条件下微型床的相界面积为它的5~10倍,是微型流化床具有更大体积传质系数的主要影响因素。     

Numerical determination of fluid-to-particle mass and heat transfer coefficients in packed bed reactors

A method based on particle-resolved CFD is built and validated, to calculate the fluid-to-particle mass and heat transfer coefficients in packed beds of spheres with different tube-to-particle diameter ratios (N) and of various particle shapes with N = 5.23. This method is characterized by considering axial dispersion. The mass and heat transfer coefficients increase by 5%–57% and 9%–63% after considering axial dispersion, indicating axial dispersion should be included in the method. The mass and heat transfer coefficients are reduced as N decreases. The catalyst particles without inner holes show higher mass and heat transfer coefficients than the ones with inner holes, because of unfavorable fluid flow in inner holes. The bed of trilobes has the highest mass and heat transfer coefficients, being 85% and 95% higher than the one of spheres. This work provides a versatile method and some useful guidance for the design of packed bed reactors.     

表面张力对传质过程的影响

表面张力对传质过程的影响主要是影响传质界面积,当物系为正物系时,对板式塔有较小较稳定的汽泡,对填料塔和湿壁塔,有较稳定的液膜,结果使二者均有较大的传质界面积,传质效果较好;负物系的情况相反。当液体混合物的平均表面张力较小时,也有利于形成较小较稳定的汽泡,从而有利于传质。表面张力对传质过程的影响机理相当复杂,这方面的研究工作有待深入开展。     

气液传质理论研究进展

文内对气液传质的理论研究进行了评述，并预测了未来的发展方向     

Effect of surfactants on liquid-side mass transfer coefficients in gas-liquid systems: A first step to modeling

This paper focuses on the effect of surfactants on the mass transfer parameters (volumetric mass transfer coefficient k_La and liquid-side mass transfer coefficient k_L). Tap water and aqueous solutions with surfactants (anionic, cationic and non-ionic at concentrations up to are used as liquid phases. The bubbles are generated into a small-scale bubble column having an elastic membrane with a single orifice as gas sparger. To understand the effects of the surfactants on the mass transfer, not only the static surface tension is used, but also the characteristic adsorption parameters like the surface coverage ratio at equilibrium Se. The liquid-side mass transfer coefficient is obtained from the ratio of the volumetric mass transfer coefficient (measured by a chemical method) and the specific interfacial area. These two parameters are obtained simultaneously. The methods used to obtain these parameters are described in Painmanakul et al. [2005. Effects of surfactants on liquid-side mass transfer coefficients. Chemical Engineering Science 60, 6480-6491].Whatever the liquid phase, three zones are found on the liquid-side mass transfer coefficient variation with the bubble diameter. For bubble diameters less than 1.5 mm, whatever the liquid phases, the k_L values are roughly constant at . For bubble diameters greater than 3.5 mm, the k_L values do not vary much with the bubble diameter, but depend on the surfactant concentration. For bubble diameters between 1.5 and 3.5 mm, the k_L values increase from to the value reached at 3.5 mm. This increase depends on the surfactants. Higbie's model does not represent the k_L values for bubble diameters greater than 3.5 mm, even though there is a small amount of surfactant in the liquid phase. Thus, a model is proposed for each zone described above. Explanations are also proposed for the effect of the surfactant on the k_L values for each of the above zones.     

伴有瞬时化学反应微溶固体颗粒的气液传质

为研究瞬时化学反应性固体颗粒对气液传质过程的影响,对伴有瞬时反应性固体颗粒/水浆料体系吸收气体过程进行了理论分析。考虑了固体颗粒在气液界面附近的溶解,以及固体颗粒尺寸对传质的影响,将cell模型融入溶质渗透理论,建立了气液二相间传质模型,并对模型进行了解析求解,得到了液相传质系数的解析表达式。结果显示:固含率、固体颗粒尺寸和溶解度对气液传质过程具有重要影响,液相传质系数随固含率和固体颗粒在液相中饱和浓度的增加而增大,随固体颗粒粒径增大而减小。在搅拌式反应器中利用Mg(OH)2/水浆料吸收SO2气体,对传质模型进行了实验验证。模型计算结果与实验值吻合良好。     

Prediction of liquid film mass transfer coefficients in packed columns using liquid holdup

A unique characteristic linear dimension (d), defined as the cube root of the specific liquid holdup (h_sp) in the packed column, was used to correlate successfully the liquid film mass transfer coefficient k_La for gas absorption-desorption for sparingly soluble gases in liquids below loading. To produce this simple, dimensionless correlation, k_La data reported in literature were used, covering a wide range of physical properties of liquids, packings and operating conditions. This new approach showed operating holdup as an important factor in gas liquid mass transfer.     

基于格子Boltzmann方法模拟纳米流体强化传质过程

使用Boltzmann方法对纳米流体中的传质过程进行了模拟,给出了修改后的Boltzmann方程和计算纳米流体中扩散系数的方程,通过两种方法,基于有限体积颗粒的LBE方法和基于点源颗粒的LBE方法进行了模拟,并与宣益民的实验进行了对比。最后计算了CO2在纳米流体中的扩散系数,计算结果表明,纳米流体因为其纳米颗粒的微扰动对传质有着很大的强化效果,为CO2吸收提供了一种新思路,并且证明了纳米流体的强化传质主要是靠对流传质。     

第二液相对气液二相体系传质的影响

以CO2气体-K2CO3/KHCO3水溶液吸收过程为研究体系,用酸解法测量气体被吸收的速率,通过对比试验考察了加入第2液相(有机相)对体系传质速率的影响。经过试验研究证明,第2液相的加入对气液传质过程的影响程度与加入的物质有关,在试验条件下甲苯对体系强化作用高于异辛醇和庚烷对体系的强化作用。当第2液相加入量较小时,随加入量的增加,其对气液传质过程的促进作用增强,但当第2液相加入量较大时,这种作用则不明显。同时第2液相对传质作用的影响与流动场有关,增加流动场的搅动有助于强化气液传质作用。     

卧式搅拌釜气液传质性能研究

在 50L卧式搅拌釜内,采用氧电极法测量纯水 O2 体系的液侧容积传质系数kLa, 研究搅拌弗鲁德数Fr、桨叶尺寸和液含量等对kLa的影响。随着Fr提高,kLa增大;桨径、桨宽、叶片数和层间距与kLa有关系,而层间夹角对kLa影响不大;随液含量的增加kLa先缓慢升高而后降低,且峰形和峰值随Fr的增大而发生变化。研究结果可供四氟乙烯等聚合釜搅拌桨设计优化和工程放大参考。     

电磁场作用下的强化传质研究进展

总结了电场、磁场和电磁场作用下强化传质的一些实验与理论工作,分析了3种强化传质方式在传质对象和传质机理方面的一些不同.进行比较后显示,电磁场强化传质的应用更加广泛,其强化传质机理可解释为:电磁场与物质的相互作用改变了物质的活性,降低了传质过程的活化能,从而使扩散得到增强.最后介绍了微波非热效应的一些实验与理论研究进展.研究表明,一些化学反应、陶瓷烧结和萃取等过程的传质得到强化确实是由于微波非热效应的作用.     

Prediction of mass transfer coefficients in a pulsed disc and doughnut extraction column

A study of the mass transfer performance for a pulsed disc and doughnut extraction column has been presented for a range of operating conditions. The mass transfer performance has been investigated for both directions of mass transfer. This study has examined the mass transfer coefficients which has incorporated the effects of back‐mixing in the continuous phase. The effect of operating variables including pulsation intensity and dispersed and continuous phase velocities on volumetric overall mass transfer coefficient has been investigated. The experiments showed that mixer‐settler, transition and emulsion regimes exist in the column depending on the pulse characteristics. In the present work, effective diffusivity is substituted for molecular diffusivity in the Gröber equation for estimation of overall mass transfer coefficients. The enhancement factor is determined experimentally and there from a single empirical correlation is derived for prediction of enhancement factor in terms of Reynolds number, holdup and Eötvös number for all operating regimes and each mass transfer direction. The experimental results are in very good agreement with the values calculated by the proposed equation. © 2011 Canadian Society for Chemical Engineering