MASS TRANSFER FROM FLAT PLATES TO POWER-LAW FLUIDS IN LAMINAR FLOW

Mass transfer from vertical flat plates to water and 0.5 to 1.5% aqueous CMC solutions is measured in the Reynolds number range of 10^{- 2}to 6.0 x 10₃. Blasius analysis has been found to be valid only up to a Reynolds number of 100, below which Graetz-Leveque solution is more appropriate.     

流动注入法测定药品中新斯的明

建立了测定药品中新斯的明的流动注入法,在ｐＨ＝８的条件下,新斯的明与溶解在１,２－二氯乙烷中的四溴酚酞乙酯形成离子缔合物并进入有机相,采用装有双重多孔聚四氟乙烯膜的相分离器分离有机相和水相。测定了１×１０－７～５×１０－７ｍｏｌ／Ｌ范围内的标准曲线,相对标准误差为０．５％,分析频度达２４次／ｈ,能实现自动快速且准确可靠,有较高的灵敏度。     

MASS TRANSFER INTO LAMINAR GAS STREAMS IN WETTED-WALL COLUMNS WITH COUNTERCURRENT GAS-LIQUID FLOW

The effect of the gas and liquid flow rates on the mass transfer rate in laminar gas streams in wetted-wall columns with countercurrent gas-liquid flow was studied. An approximate analytical solution was obtained for the average gas-phase Sherwood number as a function of the gas-phase Graetz number and the dimensionless interfacial gas velocity. Experiments were carried out on the absorption of ammonia into aqueous sulfuric acid solution and of methanol vapor into water, using two columns of different lengths. The agreement between the experimental and the predicted effects of both gas and liquid flow rates on the gas-phase mass transfer rate was found to be fairly good.     

MASS TRANSFER INTO LAMINAR GAS STREAMS IN WETTED-WALL COLUMNS WITH COUNTERCURRENT GAS-LIQUID FLOW

The effect of the gas and liquid flow rates on the mass transfer rate in laminar gas streams in wetted-wall columns with countercurrent gas-liquid flow was studied. An approximate analytical solution was obtained for the average gas-phase Sherwood number as a function of the gas-phase Graetz number and the dimensionless interfacial gas velocity. Experiments were carried out on the absorption of ammonia into aqueous sulfuric acid solution and of methanol vapor into water, using two columns of different lengths. The agreement between the experimental and the predicted effects of both gas and liquid flow rates on the gas-phase mass transfer rate was found to be fairly good.     

APPROXIMATION OF LAMINAR FLOW FIELD IN RECTANGULAR CHANNELS WITH SUCTION/INJECTION ALONG ONE WALL

An approximated analytical solution of the Navier–Stokes equations describing the laminar flow through a three-dimensional rectangular channel with wall suction or injection is presented. The solution is developed in terms of a stream function whose variation is described by a separation approach in combination with the polynomial approximation of the spatial velocity profiles. The approximated profiles agree well with simulated results obtained from the commercial code ANSYS CFX 10.     

ON THE LIQUID FLOW REVERSAL IN BUBBLE COLUMNS

The maximum range of the radial position within which liquid flow reversal can be expected to occur in zero net liquid flow bubble columns is predicted. It is shown that existing models, that employ this position as an input parameter for predicting the liquid velocity profile, are intrinsically valid only when the flow reversal dimensiontess radius is confined to ihe narrow range of 0.644-0.707. It is demonstrated that radial positions outside this range are unacceptable on physical grounds. Guidelines for evaluating the appropriate location of the flow reversal point for typical bubble column operating conditions are proposed.     

ANALYTICAL STUDY OF HEAT TRANSFER TO LAMINAR FLOW OF NON-NEWTONIAN FLUIDS IN ANNULUS

An analytical study is made of the problem of laminar flow heat transfer to pseudoplastic fluids in a concentric circular tube annulus. The solution is obtained for simultaneously developing velocity and temperature profiles and constant wall heat flux. Constant property results are presented for different values of flow behavior index, n, and several inner to outer tube radius ratios and Prandtl numbers. Variable property solutions, with strongly temperature-dependent consistency index are obtained. The effect of viscous dissipation on the results of heat transfer is also presented.     

A SHORT-CUT METHOD FOR DETERMINING CONCENTRATION DEPENDENT DIFFUSIVITY IN LIQUID FOODS AND POLYMER SOLUTIONS FROM REGULAR REGIME DRYING CURVES

A simple method for determining concentration (water or solvent content) dependent diffusivity in liquid foods and polymer solutions from the regular regime drying curve was developed on the basis of the power-law diffusion model. The method was first tested to the drying data generated from numerical solutions of the diffusion equation with various types of concentration dependent diffusivities. The present method was found to be very simple yet accurate compared with the previous methods. Then, the drying rates of various sugar solutions experimentally obtained were analyzed on the basis of the present method to determine the moisture content dependent diffusivities.     

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.     

A SHORT-CUT METHOD FOR DETERMINING CONCENTRATION DEPENDENT DIFFUSIVITY IN LIQUID FOODS AND POLYMER SOLUTIONS FROM REGULAR REGIME DRYING CURVES

A simple method for determining concentration (water or solvent content) dependent diffusivity in liquid foods and polymer solutions from the regular regime drying curve was developed on the basis of the power-law diffusion model. The method was first tested to the drying data generated from numerical solutions of the diffusion equation with various types of concentration dependent diffusivities. The present method was found to be very simple yet accurate compared with the previous methods. Then, the drying rates of various sugar solutions experimentally obtained were analyzed on the basis of the present method to determine the moisture content dependent diffusivities.     

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

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.     

分析用水对陶瓷铅溶出量测定的影响

分析用水水质对日用陶瓷铅溶出量测定具有重要影响,CL-、SO42-、CO2等严重抑制铅的溶出,使测定结果偏低。     

INSTANTANEOUS RESPONSE OF PULVERIZED COAL PARTICLES TO FLUCTUATING TEMPERATURE IN A HOT GAS FLOW

The instantaneous temperature response of pulverized coal particles to fluctuating gas temperature in a hot airflow is investigated. The particle relaxation time for temperature is analyzed. Both numerical and analytical approaches are adopted to solve the instantaneous particle energy equation. The results obtained by the two approaches are quite close. The gas temperature fluctuation has an obvious influence on the particle instantaneous temperature, especially for particles with relatively small diameters. The effects of fluctuation intensity and frequency of the gas temperature, as well as particle Reynolds number, on the particle instantaneous temperature response are delineated. The present study provides a basis for further exploring the impacts of gas turbulence on the particle reactive behaviors.     

INSTANTANEOUS RESPONSE OF PULVERIZED COAL PARTICLES TO FLUCTUATING TEMPERATURE IN A HOT GAS FLOW

The instantaneous temperature response of pulverized coal particles to fluctuating gas temperature in a hot airflow is investigated. The particle relaxation time for temperature is analyzed. Both numerical and analytical approaches are adopted to solve the instantaneous particle energy equation. The results obtained by the two approaches are quite close. The gas temperature fluctuation has an obvious influence on the particle instantaneous temperature, especially for particles with relatively small diameters. The effects of fluctuation intensity and frequency of the gas temperature, as well as particle Reynolds number, on the particle instantaneous temperature response are delineated. The present study provides a basis for further exploring the impacts of gas turbulence on the particle reactive behaviors.     

A SIMPLIFIED MODEL FOR DETERMINATION OF MOISTURE DIFFUSIVITY OF DATE FROM EXPERIMENTAL DRYING CURVES

ABSTRACT

Experimental drying curves for Tunisia Deglet Nour dates were obtained in a laboratory dryer under different drying conditions The air temperature was varied from 30 to 69^°C, relative humidity from 11.6 to 47.1 % and air velocity from 0.9 to 2.7 m/s. A numerical method to obtain a solution of a diffusion equation in which the diffusivity depends upon temperature and moisture content has been proposed to investigate the moisture movement in a date by assuming the sample to be a homogenous infinite cylinder. To rind the fitting moisture and temperature dependent diffusivity, the calculated drying curves are compared with the observed drying curves and an empirical equation for the moisture diffusivity of the date has presented as a function of temperature and moisture. It has been shown that the moisture distribution in the date during drying can be obtained by using the empirical equation presented.     

BUBBLE FORMATION IN A TRANSVERSE HORIZONTAL LIQUID FLOW

Over a wide range of liquid velocities, gas emitted from an orifice forms a cylinder or jet of gas which disrupts by varicose instability to generate bubbles. Data is presented which extends the previous use of this model by Silberman (1957).

At liquid velocities low enough to be comparable with bubble rise velocity, bubbles are formed discretely at the orifice. Mathematical models indicate that the value of hydrodynamic mass that is effective in the horizontal direction in delaying bubble release lies between 0 and 0.5 times the displacement. The value of 0.5 is a useful predictive guide up to the point where jetting occurs and the instability model predicts a smaller bubble.     

微波消解FI-HG-AAS法测定血清中的痕量硒

建立了一种测定血清样品中痕量硒的新方法。血清样品经微波消解,将 Ｓｅ（ Ｖ Ｉ）还原为 Ｓｅ（ Ｉ Ｖ）,用流动注射氢化物发生原子吸收分光光度法测定。在优化条件下,检测限 Ｓｅ 的质量浓度为０．３ μｇ／ Ｌ。测定两种标准参考物质的结果符合标准值。该法已用于测定产妇、新生儿和成人血清中的硒。     

A SIMPLIFIED MODEL FOR DETERMINATION OF MOISTURE DIFFUSIVITY OF DATE FROM EXPERIMENTAL DRYING CURVES

Experimental drying curves for Tunisia Deglet Nour dates were obtained in a laboratory dryer under different drying conditions The air temperature was varied from 30 to 69^°C, relative humidity from 11.6 to 47.1 % and air velocity from 0.9 to 2.7 m/s. A numerical method to obtain a solution of a diffusion equation in which the diffusivity depends upon temperature and moisture content has been proposed to investigate the moisture movement in a date by assuming the sample to be a homogenous infinite cylinder. To rind the fitting moisture and temperature dependent diffusivity, the calculated drying curves are compared with the observed drying curves and an empirical equation for the moisture diffusivity of the date has presented as a function of temperature and moisture. It has been shown that the moisture distribution in the date during drying can be obtained by using the empirical equation presented.     

FULLY DEVELOPED LAMINAR FLOW IN A HELICAL TUBE OF FINITE PITCH

An alternate development of a non-orthogonal coordinate system that is useful in studying fluid flow in helical tubes in the limit of large pitch is presented. It is based on a rotating cartesian system of coordinates. An analytical solution is developed for the creeping flow limit in such tubes. Also the complete equations of motion are solved numerically for a set of parameter values (viz. pitch, radius of coil and aspect ratio) that yield an approximate square in the direction along the central helix. The ratio of the friction factor of a square helical tube to that of a square straight tube has been correlated through the use of the flow helical number.