UNSTEADY-STATE SORPTION MEASUREMENTS A TEST OF DIFFERENT METHODS TO EVALUATE THE DIFFUSIVITY FROM UNSTEADY-STATE SORPTION MEASUREMENTS

ABSTRACT

Different simple methods for evaluating the diffusivity from a sorption measurement are presented and tested when there is a surface resistance (a limited mass transfer coefficient), a non-perfect step in relative humidity or non-Fickian effects. It is concluded that the different methods have different qualities and it is impossible to give a general recommendation on which method to use. The best tactic is probably to use more than one of the methods. A knowledge of the experimental conditions will help in choosing the best method.     

THE HEAT OF SORPTION OF TIMBER

ABSTRACT

Two different methods for calculating the heat of somtion of timber are compared. One method uses thermodynamic expieasions together with the sorption equilibrium relationship given by Simpson and Rosen (1981). while the other is based on the direct measurements made by Kelsev end Clarke (1956). The latter method is most reliable for moisture contents below 0.07 kg kg^-1, where the heat of sorption is significant cowered with the latent heat of vaporisstion of water.     

THE MOISTURE SORPTION ISOTHERMS OF CEFOTAXIME SODIUM SALT

ABSTRACT

The water sorption isotherms of the cefotaxime sodium salt were determined at 30 and 40° C. Cefotaxime sodium salt was maintained at equilibrium relative humidities ranging from 40 to 80 %. Equilibrium moisture content was determined by the Karl Fischer method. The moisture sorption isotherms showed that the equilibrium moisture decrease while the temperature increase. The experimental curves of equilibrium humidity were fitted by different models (Bradley, Halsey, Henderson, Kuhn, Smith and Iglesias and Chirife and GAB). Parameters of each equations were determined by non-linear regression analysis. The best fit was obtained by Iglesias and Chirife model. The isosteric heat of moisture sorption calculated by Claussius Clapeyron equation varied from 64·45 to 48·03 kJ/mol when moisture content changed from 7 to 9·5 %.     

Choosing the right model: Case studies on the use of statistical modeldiscrimination experiments

Statistical model discrimination methods were developed to efficiently and reliably choose the ‘best’ model for a system from a set of candidate models. Three promising model discrimination techniques are compared using three chemical engineering examples in this paper. The examples were studied via computer simulations in which experimental data were generated using a known model. The use of a computer simulation allowed factors such as error magnitude to be studied at different levels in repeat runs of the program. The results indicated the exact entropy method is the best method for use with non-nested nonlinear models, while the Buzzi-Ferraris and Forzatti (1983) method is best for use with nonlinear nested models.     

DETERMINATION OF BREAKTHROUGH CURVES FOR SELECTIVE-MEMBRANE SORPTION PROCESSES

Thin layers of selective membrane materials can be arranged in a fixed-bed or column configuration by coating them onto conventional sorbent particles. The advantages are the attainment of several stages of contact in a single step and an economical use of relatively expensive selective materials. In this report, it is shown that Klein's direction-field method for the analysis of mass transfer in fixed beds can be extended to processes involving selective layers. The extended method can be implemented graphically or numerically.     

EFFECT OF DRYING METHODS ON MOISTURE SORPTION ISOTHERMS OF FUFU AT THREE TEMPERATURES

Moisture sorption characteristics for dried fufu using three drying methods at 25°C, 32°C and 45°C were determined experimentally for water activity ranging from 0.11 to 0.96. At a given temperature and water activity, the rotary dried fufu had the highest equilibrium moisture content while the sun dried had the lowest.

Four linear and four nonlinear sorption models were used to analyze the data. The linear GAB model showed the best fit while the nonlinear Bradley model was the best over the whole range of water activity in their respective groups. Also estimates of the net isosteric heats of sorption and their dependence on moisture content were presented for each product.     

PREDICTING THE SORPTION BEHAVIOUR OF GARLIC SLICES

ABSTRACT

Moisture desorption properties of fresh garlic (cv. Early Californian) were investigated at 20 °C to 70°C and relative humidities ranging from 11% to 85% using the gravimetric static method. The slices were allowed to equilibrate in a constant humidity environment (hygrostats) maintained by salt solutions. The effect of temperature and relative humidity on the equilibrium moisture content was highly significant (P<0.0001). Four models available in the literature, namely the Chung-Pfost, modified Halsey, modified Henderson and the Guggenheim-Anderson-de Boer (GAB) were evaluated (the correlation coefficient, F-ratio and plots of residuals) to determine the best fit for the experimental data. On the basis of the F-test, The modified Henderson model was found adequate and the GAB model superior for characterising the sorption behaviour of garlic slices in the temperature and water activity range investigated.     

PREDICTING THE SORPTION BEHAVIOUR OF GARLIC SLICES

ABSTRACT

Moisture desorption properties of fresh garlic (cv. Early Californian) were investigated at 20 °C to 7O° C and relative humidities ranging from 11% to 85% using the gravimetric static method. The slices were allowed to equilibrate in a constant humidity environment (hygrostats) maintained by salt solutions. The effect of temperature and relative humidity on thc equilibrium moisture content was highly significant (P < 0.0001). Four models available in the literature, namely the Chung-Pfost, modified Halsey, modified Henderson and the Guggenheim-Anderson-de Boer (GAB) were evaluated (the correlation coefficient, F-ratio and plots of residuals) to deterinhe the best fit for the experimental data. On the basis of the F-test, The modifled Henderson model was found adequate and the GAB model superior for characterising the sorption behaviour of garlic slices in the temperature and water activity range investigated.     

EFFECT OF DRYING METHODS ON MOISTURE SORPTION ISOTHERMS OF FUFU AT THREE TEMPERATURES

ABSTRACT

Moisture sorption characteristics for dried fufu using three drying methods at 25°C, 32°C and 45°C were determined experimentally for water activity ranging from 0.11 to 0.96. At a given temperature and water activity, the rotary dried fufu had the highest equilibrium moisture content while the sun dried had the lowest.

Four linear and four nonlinear sorption models were used to analyze the data. The linear GAB model showed the best fit while the nonlinear Bradley model was the best over the whole range of water activity in their respective groups. Also estimates of the net isosteric heats of sorption and their dependence on moisture content were presented for each product.     

STUDY ON SORPTION ISOTHERMS OF SHRIMP BEADS

Sorption isotherms of shrimp heads ( adsorption and desorption ) were analyzed by the microclimate method as temperatures of 30, 45 and 60°C and conditions for shrimp heads conservation by drying were determined. Equilibrium time was reduced from normally 2-3 weeks to only 5-8 days by employing sulfuric acid at different concentrations and vacuum. The results were adjusted by Henderson and G.A.B. models and correlation coefficients were up to 0.9900 for the last model.     

STUDY ON SORPTION ISOTHERMS OF SHRIMP BEADS

ABSTRACT

Sorption isotherms of shrimp heads ( adsorption and desorption ) were analyzed by the microclimate method as temperatures of 30, 45 and 60°C and conditions for shrimp heads conservation by drying were determined. Equilibrium time was reduced from normally 2–3 weeks to only 5–8 days by employing sulfuric acid at different concentrations and vacuum. The results were adjusted by Henderson and G.A.B. models and correlation coefficients were up to 0.9900 for the last model.     

UNIFICATION OF FRUIT WATER SORPTION ISOTHERMS USING ARTIFICIAL NEURAL NETWORKS

The chemical composition, water activity, temperature and equilibrium moisture content (EMC) for 10 selected fruits were determined. Two methods of water sorption modeling, the GAB equation and the artificial neural network (ANN) method, were compared for their ability to predict water sorption behavior. Unlike the GAB equation, which uses only physical data for modeling, the ANN method uses both physical and chemical compositional data to make predictions. The ANN was superior, in most cases, to that of the GAB equation, in predicting EMC. This superiority was due to the availability of the additional chemical compositional information. The ANN method could predict EMC with a mean relative error of 9.85% and a standard error (S _x ) of 1.59% EMC. The correlation coefficient (r ²) of the relationship between the actual and predicted values of equilibrium moisture content obtained by the ANN was 0.9938. The ANN model was able to show a temperature dependent crossing of water sorption isotherms, due to the dissolution of sugar crystals in the fruit. The ANN was also able to predict the extent of crossing, depending upon differences in the individual fruit chemical composition.     

UNIFICATION OF FRUIT WATER SORPTION ISOTHERMS USING ARTIFICIAL NEURAL NETWORKS

The chemical composition, water activity, temperature and equilibrium moisture content (EMC) for 10 selected fruits were determined. Two methods of water sorption modeling, the GAB equation and the artificial neural network (ANN) method, were compared for their ability to predict water sorption behavior. Unlike the GAB equation, which uses only physical data for modeling, the ANN method uses both physical and chemical compositional data to make predictions. The ANN was superior, in most cases, to that of the GAB equation, in predicting EMC. This superiority was due to the availability of the additional chemical compositional information. The ANN method could predict EMC with a mean relative error of 9.85% and a standard error (S_x) of 1.59% EMC. The correlation coefficient (r²) of the relationship between the actual and predicted values of equilibrium moisture content obtained by the ANN was 0.9938. The ANN model was able to show a temperature dependent crossing of water sorption isotherms, due to the dissolution of sugar crystals in the fruit. The ANN was also able to predict the extent of crossing, depending upon differences in the individual fruit chemical composition.     

窑体一维非稳态散热过程的计算机模拟

应用完全隐式差分格式给出了多层平壁结构窑墙一维非稳态导热过程在变导热系数、变比热系数条件下的节点温度计算方法,提出了一般窑炉周期性循环工作时窑体内部节点温度计算的改进方案。计算结果表明,采用这种数值分析方法计算窑体非稳态过程的温度分布和积散热是非常适宜的。     

铁矿石中测铁实验方法比较与优化

采用不同方法测铁矿石中铁含量,即有汞法和无汞法,有汞法方法成熟,准确度高,但使用了氯化汞,环境不友好,对周围环境造成污染。无汞法则避免了汞对环境的污染,且无汞法有不同样品预处理方法。但是不同方法之间存在系统误差,准确度不能满足要求。用不同方法同时测定标样和试样,在对数据进行显著性检验,对不同实验方法进行比较和优化选择。寻找到最佳实验方法和测定条件,可在实验教学中推广采用。     

SORPTION PROPERTIES OF SYNTHETIC FERRIERITE

Limiting sorption volumes of the hydrogen form of a synthetic ferrierite sample were determined for sorbates--water, methanol, propane, hexane, and o-, m-, p-xylenes--at 298 K and at a relative pressure of P/P o = 0.5 using a gravimetric sorption apparatus. Methanol, which has a kinetic diameter significantly smaller than the pore dimensions, was sorbed relatively rapidly and by the greatest amount. The sorption rates of other sorbates were very slow and for some it took several days for equilibrium to be established. The results indicated that, although their kinetic diameters are similar, the adsorption behavior of propane and hexane are quite different. Hexane is able to fill only ten-membered ring channels whereas propane is able to fill both ten- and eight-membered ring channels, at least partially. The inability of the hexane molecules to be sorbed into eight-membered ring channels is attributed to chain length effect. Xylene isomers are sorbed by the H-ferrierite but to smaller extents, consistent with the significantly larger kinetic diameters of these molecules compared to the reported pore dimensions of ferrierite. Among the xylene isomers, p-xylene, with the smallest kinetic diameter of three isomers, is sorbed to a greater extent than either o-xylene or m-xylene.     

特征函数法在动力学模型研究中的应用

用特征函数法求解分布参数系统中的偏微分方程，状变量用包含特征函数的双正交基函数展开，可以降低方程组维数，比较动态实验获得的特征函数与模型计算值，作为竞争模型鉴别依据，并以丁烯氧化脱氢作为对象，说明该方法在动态动力学模型参数与模型鉴别上有的有效性。     

THE INFLUENCE OF TEMPERATURE ON SORPTION ISOTHERMS OF PROTEIN-CONTAINING MIXTURES

ABSTRACT

This paper presents a method for calculation of water sorption isotherms for multicomponent mixtures at different temperatures from mass fractions and sorption isotherms of components at a reference temperature. Additionally, Krischer's coefficients are required for the components. To compare experimental and calculated data, investigations on whey protein concentrates were carried out.     

THE INFLUENCE OF TEMPERATURE ON SORPTION ISOTHERMS OF PROTEIN-CONTAINING MIXTURES

This paper presents a method for calculation of water sorption isotherms for multicomponent mixtures at different temperatures from mass fractions and sorption isotherms of components at a reference temperature. Additionally, Krischer's coefficients are required for the components. To compare experimental and calculated data, investigations on whey protein concentrates were carried out.     

AN UNSTEADY-STATE TUBULAR REACTOR WITH THREE-DIMENSIONAL DISPERSION

A tubular reactor model with dispersion in three spatial dimensions, namely in the radial, axial and angular directions, is considered; and its analytical solution for an arbitrary non-uniform initial concentration distribution and an arbitrary non-uniform time-varying feed is obtained. Some special cases are deduced and the relationships between the three-dimensional dispersion model and two or one dimensional dispersion models are elucidated.