DIFFUSION COEFFICIENT OF OXYGEN IN LIQUIDS

The laminar dispersion of a solute in a capillary tube is used to measure diffusion coefficient of oxygen in liquids. A Polarographic type oxygen microelectrode is used to detect the pulse. Such a procedure overcomes the problems of measuring dissolved gases and makes it possible to apply this well known technique to oxygen-liquid systems. The results are in agreement with literature values     

NONDESTRUCTIVE MEASUREMENT OF MOISTURE DIFFUSION COEFFICIENT IN WOOD DRYING

The computer tomography(CT image of wood was analyzed to estimate the moisture content from CT number. Comparing moisture contents, densities and CT numbers, moisture distributions were nondestructively determined by CT numbers detected with the scanner.

By periodically measuring CT images of the same cross section of specimens in drying, change of moisture distribution was computed. The coefficients of moisture movement at given positions inside the specimen were directly calculated from Fick's Law with known values of moisture content change, distance and drying time.

The diffiion coeficient was described as a function of various driving forces of moisture content, partial vapor pressure and chemical potential of moisture in wood. The results were comparable to data in the literature. Furthermore, it is shown that diffusion coefficients based on moisture content varies as a curve with the maximum value at about 15% m.c. during drying, and that the moisture content is actually adaptable to the driving force for moisture movement in wood because of capability over wide moisture content range.     

NONDESTRUCTIVE MEASUREMENT OF MOISTURE DIFFUSION COEFFICIENT IN WOOD DRYING

ABSTRACT

The computer tomography(CT image of wood was analyzed to estimate the moisture content from CT number. Comparing moisture contents, densities and CT numbers, moisture distributions were nondestructively determined by CT numbers detected with the scanner.

By periodically measuring CT images of the same cross section of specimens in drying, change of moisture distribution was computed. The coefficients of moisture movement at given positions inside the specimen were directly calculated from Fick's Law with known values of moisture content change, distance and drying time.

The diffiion coeficient was described as a function of various driving forces of moisture content, partial vapor pressure and chemical potential of moisture in wood. The results were comparable to data in the literature. Furthermore, it is shown that diffusion coefficients based on moisture content varies as a curve with the maximum value at about 15% m.c. during drying, and that the moisture content is actually adaptable to the driving force for moisture movement in wood because of capability over wide moisture content range.     

EFFECTIVE DIFFUSION COEFFICIENT OF ACTIVE SOLVENTS IN COMPOSITE POLYMERIC MATERIALS

A method and a device for determination of the effective diffusion coefficient of active solvents in composite polymeric materials (CPM) based on cellulose derivatives are proposed and examined. This method accounts for anomalous mass transfer phenomena, considerable shrinkage and changes of sorption capacity of the CPM specimen allowing selection of the rational technological regime. Results of experimental studies on diffusion of acetone and ethanol in cellulose nitrate with various degrees of substitution are given as examples.     

EFFECTIVE DIFFUSION COEFFICIENT OF ACTIVE SOLVENTS IN COMPOSITE POLYMERIC MATERIALS

ABSTRACT

A method and a device for determination of the effective diffusion coefficient of active solvents in composite polymeric materials (CPM) based on cellulose derivatives are proposed and examined. This method accounts for anomalous mass transfer phenomena, considerable shrinkage and changes of sorption capacity of the CPM specimen allowing selection of the rational technological regime. Results of experimental studies on diffusion of acetone and ethanol in cellulose nitrate with various degrees of substitution are given as examples.     

分子吸附对聚乙烯醇在氧化铝粉末压缩体中扩散系数的影响

利用氧化铝粉末压缩球状体和Ｆｉｃｋ第二扩散定律,系统地研究了聚乙烯醇在多孔介质和实验系统ｐＨ值为８．４０±０．２条件下的扩散行为,以及聚乙烯醇在球体外表面吸附对扩散系数的影响．实验结果和相应计算得到的扩散系数表明：发生在氧化铝表面的分子吸附,不仅导致扩散平衡状态时的Ｍｔ（聚乙烯醇在时间ｔ的扩散量）高于理论计算值Ｍ∞,而且使实验初始阶段计算的扩散系数远大于其它过程扩散系数．由分子吸附产生的实验误差和扩散系数计算误差,可通过修正浓度分配系数Ｋ,或者直接从Ｍｔ中去除可能存在的吸附量得到解决．     

AN INVERSE MOISTURE DIFFUSION ALGORITHM FOR THE DETERMINATION OF DIFFUSION COEFFICIENT

The finite difference approximation is applied to estimate the moisture-dependent diffusion coefficient by utilizing test data of isothermal moisture desorption in northern red oak (Quercus rubra). The test data contain moisture distributions at discrete locations across the thickness of specimens, which coincides with the radial direction of northern red oak, and at specified times. Also, the rate of moisture variation at each specified time and location must be known or correctly estimated. The functional form of the diffusion coefficient as well as the boundary conditions at the surfaces are not known a priori. The resulting system of finite difference equations defines an inverse problem, whose solution may be sensitive to small changes of input data. Results indicate that the diffusion coefficient increases with increasing moisture content below the fiber saturation point, which defines the upper limit applied by the diffusion theory.     

AN INVERSE MOISTURE DIFFUSION ALGORITHM FOR THE DETERMINATION OF DIFFUSION COEFFICIENT

The finite difference approximation is applied to estimate the moisture-dependent diffusion coefficient by utilizing test data of isothermal moisture desorption in northern red oak (Quercus rubra). The test data contain moisture distributions at discrete locations across the thickness of specimens, which coincides with the radial direction of northern red oak, and at specified times. Also, the rate of moisture variation at each specified time and location must be known or correctly estimated. The functional form of the diffusion coefficient as well as the boundary conditions at the surfaces are not known a priori. The resulting system of finite difference equations defines an inverse problem, whose solution may be sensitive to small changes of input data. Results indicate that the diffusion coefficient increases with increasing moisture content below the fiber saturation point, which defines the upper limit applied by the diffusion theory.

     

THE TWO-THIRDS POWER MODEL FOR PREDICTING DIFFUSION COEFFICIENTS IN LIQUIDS

Most of the models found in the literature for predicting diffusion coefficients in liquids take the viscosity of the solution as inversely proportional to the diffusivity. A model (previously derived for sucrose-water system)which considers the viscosity raised to the two-third power, is evaluated here using published data for the Benzene—Cylohexane, Ethanol-Water and Acetone-Chloroform systems. These results, and results for the sucrose-water system are compared with the experimental values, and with those obtained using the Hartley—Crank equation. Better agreement with the experimental values at low and in the middle of the concentration range was found when diffusivities were calculated using the model proposed than when using the Hartley-Crank equation.     

硝酸银显色法测量混凝土氯离子表观扩散系数

研究了硝酸银显色法快速测量混凝土中氯离子表观扩散系数。将14组混凝土试件分别在16.5%与3.5%NaCl溶液中浸泡90d和300d,用AgNO_3显色法及NT Build 443法测量其氯离子表观扩散系数(D_A和D_N)。结果表明:用浸泡液浓度为表面氯离子浓度情况下,当表层氯离子浓度与浸泡液氯离子浓度相近时,D_A与D_N值相近;浸泡90 d时,一部分D_A与D_N值相近;浸泡300 d时,所有的D_A与D_N均十分相近。测量的表层氯离子浓度作为表面氯离子浓度时,所有D_A和D_N均十分接近。因此,合理确定表面氯离子浓度后,硝酸银显色法可以快速且较为精确地测量混凝土氯离子表观扩散系数。     

MASS TRANSFER AND DIFFUSION COEFFICIENT DETERMINATION IN THE WET AND DRY SALTING OF MEAT

Dehydrated salted meat is widely used in Brazil as a very important source of animal protein. The main objective of this kind of processing is water removal. initially by osmotic pressure changes and then by drying, resulting in a product with intermediate moisture levels.

In this work, mass transfer and salt diffusion in pieces of meat submitted to wet and dry salting were studied. Slabs of beef m. trapezius with an infinite plate geometry were salted in a NaCl saturated solution or in a dry salt bed, at two temperatures (10 and 20°C) and different time exposures (120 min and 96 hours). Equilibration studies were extended up to six days.

It was observed that water loss increased with salt uptake, for increasing periods of times. At 20°C the moisture loss was higher than it was at 10°C in both salting processes. On the other hand, the kinetics of salt uptake and moisture loss were of greater importance in the process of dry salting than in that of wet salting.

The salt diffusion coefficient for wet salting was 0.26 × 10^-10m²/s at20°C and 0.25 × 10^-10 m²/s at 10°C and for the dry salting the values were 19.37 × 10^-10 m²/s at 20°C and 17.21 × 10^-10 m²/s at 10°C.     

THE INFLUENCE OF AIR TEMPERATURE ON EFFECTIVE DIFFUSION COEFFICIENT OF MOISTURE IN THE FALLING RATE PERIOD

ABSTRACT

The convection drying of spheres of Al-Ni catalyst and thin clay plate was investigated on a laboratory scale. The aim of the investigation was to determine the mechanism of moisture transfer within the firm sample skeleton.

By measuring the mass loss and the surface temperature of the samples during the drying process, basic dependencies necessary to describe the process kinetics was obtained. Found functional dependencies show high level of correlation with experimental data. Exponential model parameters are dependent of air temperature and velocity, and the type of the examined material.

The applicability of the chosen model to describe the drying kinetics is proven regardless of drying material origin and geometry, The comparison of different drying experiment and determination of the average diffusional coefficient at given experimental conditions is enabled.     

COMPOSITION DERIVATIVES OF ACTIVITY COEFFICIENT MODELS (FOR THE ESTIMATION OF THERMODYNAMIC FACTORS IN DIFFUSION)

Derivatives of activity coefficient models are needed for the evaluation of the thermodynamic factors that arise in the equations that describe diffusion in multicomponent systems. A general framework for the evaluation of these thermodynamic factors is presented together with specific results for the Margules, Van Laar, Wilson, NRTL and UNIQUAC activity coefficient models.     

二氧化钛厚膜钯表面扩散状态对氧气响应特性影响

利用二氯化钯(PdCl2)溶液浸渍法,研究了二氧化钛(TiO2)厚膜钯(Pd)原子表层扩散对氧气响应特性的影响.扫描电子显微镜显示:Pd扩散后厚膜表面均匀分布着纳米级Pd晶粒.利用Kroger-Vink方程分析了不同扩散时间下对应的lnR-lnpo2曲线,针对不同斜率的曲线,用缺陷方程分析了Pd元素的分布状态.样品响应特性的伏安法测试结果显示:820℃,2h扩散的敏感膜具有理想灵敏度和响应时间.研究结果表明:Pd元素在敏感膜表面形成了纳米级Pd晶粒,并在TiO2厚膜表层中存在着少量的钯间隙原子(Pdi)及替位钯离子(Pd2 ).合理的扩散温度和扩散时间,可获得表层Pd氧化量最少、扩散浓度合适的敏感膜,进而获得效果理想的厚膜氧敏材料.     

ON THE METHODS FOR THE DETERMINATION OF THE OXYGEN TRANSFER COEFFICIENT IN MECHANICALLY AGITATED VESSELS

This paper reports on the determination of the overall oxygen transfer coefficient in mechanically agitated vessels. Many variants of the sulfite oxidation method are compared with the dynamic method. A new variant of the sulfite oxidation method, called the reaction time method, is proposed. Overall oxygen mass transfer coefficients were obtained with two probes having significantly different time constants and for various agitation levels. The advantages and disadvantages of the main methods used for the determination of the oxygen transfer coefficient are reviewed and discussed.     

矩形截面气升式环流反应器中非牛顿流体的气含率与传质系数的研究

研究了一种矩形截面气升式环流反应器,用幂律τ=η_ογ~n(n<1)来表示流体流变学特性的变化.在这类反应器中,假塑性非牛顿流体的气含率ε_g与传质系数K_La的变化规律可用半经验关联式表示ε_g=0.2535(η_ο5000~(n-1))~(-0.161)(1+A_d/A_r)~(-0.434)u_(gr)~(0.856-0.161n)K_La=0.0192(η_ο5000~(n-1))~(-0.902)(1+A_d/A_r)~(-1.228)u_(gr)~(1.955-0.902n)并讨论了该类反应器结构及运行状况,流体性质变化时,反应器传质动力学特性、流动特性和操作弹性变化的规律.     

SrFe1.5-xCoxOy混合导体的制备及氧化扩散研究

详细研究了混合离子导体ＳｒＦｅ１．５－ｘＣｏｘＯｙ（ｘ＝０．０－０．５）的相组成和氧化学扩散性质。Ｘ射线衍射和扫描电镜分析表明：该体系随Ｃｏ含量的增加由Ｓｒ４Ｆｅ６－ｘＣｏｘＯ１３＋δ层着相逐步变为含钙钛矿等物相的多相区。     

A DIFFUSION MODEL WITH A MOISTURE DEPENDENT DIFFUSION COEFFICIENT FOR PARBOILED RICE

A mathematical model describing moisture migration by diffusion in a solid sphere with variable diffusion coefficient is proposed. An analytical expression for dependence of the diffusion coefficient with moisture content was derived based on the assumption that the activation energy for diffusion varies linearly with the desorption energy.

The expression for moisture dependence of diffusion coefficient was used to simulate drying of parboiled rice in the temperature range 50-90°C. The mathematical model shows good agreement between observed and predicted drying rate curves.     

用改进的Eyring方程推算无限稀释扩散系数

在Ｅｙｒｉｎｇ绝对速率理论的基础上，提出一个关联扩散自由体积的关系式，从而得到改进的扩散系数计算方程，可从纯物质粘度推算无限稀释扩散系数，方程不含任何待定参数．对８２个各类体系共３３２点扩散系数数据，计算平均相对偏差为１２．１％，而Ｗｉｌｋｅ－Ｃｈａｎｇ方程对同样体系的计算偏差为１４．８％，Ｓｉｄｄｉｑｉ－Ｌｕｃａｓ方程的偏差为１２．３％．     

THE TEMPERATURE COEFFICIENT OF VISCOSITY AND ITS RELATION TO SOME OTHER PROPERTIES OF LIQUIDS AND GLASSES*

A possible connection between the temperature coefficient of viscosity (not the viscosity itself), the latent heat of fusion or some similar work-function, and the absorption spectrum of liquids and glasses is discussed. The three things seem to be connected in a fairly clear and simple manner. It is shown, for instance, that from viscosity data alone it is possible to predict the position of the ultra-violet absorption band in glasses, and the black color of pitch. Also, that at high temperatures the ultra-violet absorption band invades the visible spectrum and migrates down into the infra-red, and that at room temperature the viscosity of typical soda-lime-silica glasses is of the order 1070 poises. A meaning is attached to the term “viscosity” at temperatures at which it can not be measured mechanically, and a means of tracing it optically down to absolute zero is suggested.