Flow characteristics of large oscillating drops in liquid-liquid systems

A study was made of the flow characteristics of large oscillating drops of pure liquid-liquid systems, using a thermostatically-controlled, rising drop column, 50 mm in diameter and 1000 mm in length. Mirrors in the jacket enabled front and side views of drops to be photographed simultaneously. Single drops in the size range 5–10 mm were investigated with both mutually-saturated phases and when the solute was being transferred from the dispersed phase. The systems studied were (1) toluene and acetone (dispersed)-water (continuous), and (2) n-heptane and acetone (dispersed)-water (continuous). Acetone concentrations were varied up to 3.75 kmol/m³. The oscillations of a travelling drop were asymmetrical; therefore, the amplitude cannot be expressed accurately in terms of only two axes. The area change of the drop compared to that of a sphere of equal volume ‘ε’, was shown to represent the amplitude accurately. The periods of droplet oscillation were uniform for the mutually saturated systems of constant physical and flow properties but changed when mass transfer was taking place. The interfacial tension exerted a marked effect on the amplitude, which also depended upon the oscillation frequency. The amplitude changed with droplet size in a similar manner to the terminal velocity, i.e. it increased with increasing size until it reached a maximum, subsequently decreasing less rapidly. The drag coefficient increased with increasing rate of mass transfer from the drop. Correlation of the results and the area eccentricity ‘ε’ by dimensional analysis embracing all possible parameters and physical properties affecting drop oscillation, resulted in the correlation ε = 0.22 Sr^0.42 We^?0.53 M^0.13 with a mean deviation of ± 14%. This will facilitate more accurate prediction of the interfacial area for mass transfer calculations, relating to equipment containing droplets in the oscillating regime.     

Mathematical modeling and steady-state analysis of a scheibel extraction column

The steady-state behavior of a nine-stage Scheibel extraction column was modeled and simulated using a back flow stagewise model. Steady-state experiments were conducted, using the system water-acetone-toluene, for three phase ratios and three agitator speeds. The mathematical model was validated with the experimental concentration profiles by a single parameter fitting technique with an unconstrained optimization algorithm. Steady-stage analysis of the experiments was performed for a further control study. The calculated steady-state gain matrices were used for interaction analysis using different steady-state analysis methods, e.g. Bristol numbers, Condition numbers, Morari Indexes of Integral Controllability, and Niederlinski Indexes. The results indicate that both agitator speed and phase ratio have a substantial influence on the control structure. Dynamic analysis should therefore be performed to verify the optimum control method for this process.     

Volatiles Retention in the Drying of Skin Forming Materials PART 1: Materials Which Gelatinise at Moderately High Temperatures

Single droplets were dried whilst suspended from a rotating thermocouple in a horizontal wind tunnel, to study the effect of skin formation upon the retention of flavours. Native rice starch, wheat starch, or dextrin were used to encapsulate ethanol as a simulated flavour. The ethanol content of the dried droplets was measured using gas liquid chromatography and the crusts were examined using a scanning electron microecope. The effects of variations in encapsulant concentration, drying air temperature, and air flow rates upon flavour retention were determined.

With the rice starch, the 'final retention' of ethanol, defined as the ethanol content of the droplet after drying for ten minutes, was largely independent of initial solids     

Measuring occupational difficulty: A construct validation against training criteria.

Burtch, Lipscomb, and Wissman's (1982) occupational learning difficulty index attempts to measure the difficulty of occupations by aggregating workers' evaluations of task learning time. In the present study we examined the construct validity of this job analysis index. To accomplish this, 48 different occupational training programs were described in terms of 15 training content variables, 6 student characteristics variables, and 7 training performance variables. The results, obtained in a correlational analysis, indicated that the occupational learning difficulty index yielded an interpretable pattern of relationships with the training content and performance variables. We conclude that this task learning time index displays some construct validity as a measure of occupational difficulty and, therefore, should prove of value in designing training, manpower allocation, and job evaluation systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Introduction by Guest Editors

International Journal of Computer Vision -     

Guest Editorial: Statistical and Computational Theories of Vision: Modeling,Learning, Sampling and Computing,Part I

International Journal of Computer Vision -     

A Socio-Technical Approach to Systems Design

This paper examines how the structure of organisations is changing as a result of the global market and new technology and it discusses how these changes are affecting the nature of work. It identifies systems design as a problem-solving activity that requires a multidisciplinary approach, examines the current and new problems of complex systems design and describes how a socio- technical approach which takes account of technical, organisational, economic and social needs can assist the creation of humanistic and effective systems for tomorrow’s world.     

A study of mass transfer from single large oscillating drops

A study was made of mass trasfer rates from single large oscillating drops of pure liquid-liquid systems, in the size range of 5 to 10 mm. A thrermostatically-controlled, 50 mm in diameter, 1000 mm long, rising drop column was used, in which mirrors in the jacket enabled front and side views of drops to be photographed simultaneously. The systems studied were (1) toluene and acetone (dispersed)-water (continuous), and (2) n-heptane and acetone (dispersed)-water (continuous). High concentrations of acetone (up to 3.75 kmol/m³) were used to examine the effect of different parameters on the mass transfer rate, frequency and amplitude of oscillation in countercurrent operation. Previous theories and empirical correlations [2–6, 12, 13, 15] for the prediction of overall mass transfer coefficients showed large deviations from measured values. These may have aarisen because the models do not represent droplet oscillation accurately, and/or apply only to oscillations of small droplets. Fair agreement was obtained for small oscillating droplets as low solute concentrations. The oscillations of a travelling drop were asymmetrical; the period of oscillation was uniform for mutually-saturated systems but changed when mass transfer was taking place. The periods were longer than those predicted by the Lamb [7] and Shroeder and Kintner [37] correlations. Terminal velocities predicted from literature correlations [32, 34] did not give reasonable agreement with experimental data when there was mass transfer of solute. The drag coefficient increased with increasing mass transfer rate from the drop. Correlation of the results and the dispersed phase mass trasfer coefficients by dimensional analysis resulted in the correlation

1 List of symbols at the end of the paper.

with a mean deviation of ±23%, by insertion of experimental oscillation frequency data. This will facilitate more accurate prediction of the dispersed phase mass transfer coefficients relating to equipment containing droplets in the oscillating regime, e.g. pulsed columns or agitated tanks.     

Kinetics of sulfur transfer from H2S to Fe1-xS

The rate of sulfur transfer across the gas/solid interface involving H₂S(g) and Fe_1-xS surface has been investigated using resistance relaxation measurements at 600°C. The rate of the oxidation reaction incorporating sulfur into Fe_1-xS has been found to decrease with sulfur activity (a_S) in the sample as (a_S)^-2/3, while the rate of the reduction reaction corresponding to sulfur loss is found to increase with the sulfur activity as (a_S)^1/3. The kinetic finding has been combined with the appropriate defect models for FeS to identify the rate limiting step for the sulfur transfer reaction from H₂S to FeS. Accordingly, the rate limiting step has been identified to be: H₂S(g) + 2e^-\rightleftharpoons S^2-(ad) + H₂(g). This revised version was published online in July 2006 with corrections to the Cover Date.