In this study, GAS phase HOLDUP in a GAS-liquid bubble column reactor was experimentally studied. To conduct experiments, a bubble column with a height of 54 cm and a diameter of 10. 4 cm was applied. The studied systems include water-air, GASoline-air, and Behran oil-air. Experiments were carried out in the range of 400-50 rpm agitator. Based on the Buckingham π,theorem, a semi-experimental model for GAS phase HOLDUP was presented. The results showed that with increasing viscosity from 0. 001 to 0. 0136 GAS phase HOLDUP loss due to high adhesion of bubbles at high viscosity and also the increase of bubble size at the output from the distributor decreases from 0. 41 to 0. 333. Among the selected systems, the GAS phase HOLDUP of the GAS-air system was maximized. The results also showed that in materials with low viscosity, the GAS phase reduction was due to the formation of liquid vortex movement and air canalization by the agitator. The best agitator speed to increase the GAS phase HOLDUP at water and oil are 150 and 400 rpm, respectively.

Bubble and slurry bubble column reactors usually work under pressures beyond the atmosphere in the industries. Although many studies have been done about bubble and slurry bubble column reactors, experimental studies under elevated pressure are very limited. In this study, the effects of pressure and slurry concentration on the GAS HOLDUP have been investigated by using pressure difference tests. The experiments of this study are made under pressures up to 18 bar and paraffin and silica are used as the liquid and solid contents. Increasing the operation pressure leads to an increase in GAS HOLDUP. It is also found out that the effect of pressure is vanished by increasing the slurry concentration. The experiments are performed in a column with a diameter of 16 cm and a height of 2.8 m. The GASes used are nitrogen and air. Finally, a new experimental correlation is developed as a function of GAS density (rg), superficial velocity of GAS (Ug), slurry density (rSL), slurry viscosity (mSL), and liquid surface tension (sL); the correlation is obtained by using the data extracted from this investigation and is in good agreement with the experimental data.

Existing liquid HOLDUP models are generally based on low GAS and liquid velocities. In order to extend the applicable range of existing liquid HOLDUP prediction models and improve its prediction accuracy, a of GAS-liquid two-phase flow experiment was carried out using a pipe of inner diameter 60mm and length of 11. 5m. The superficial GAS and liquid velocity ranges were 14. 07~56. 50m/s and 0. 205~1. 426m/s, respectively. The results indicate that the liquid HOLDUP decreases with the increase of the superficial GAS velocity and increases with the increase of the superficial liquid velocity. A new annular flow model for calculating low liquid HOLDUP in horizontal pipe was developed and presented considering the relationships between the friction factor ratio of liquid phase and GAS-liquid interface as well as the superficial Reynolds number of GAS and liquid. The predictions of the model are found to be accurate with an average absolute error of 4. 8%. Further, on the basis of the Beggs-Brill model and the horizontal pipe model established in this paper, a new liquid HOLDUP model for different angles was given. It was observed the resultant model is also accurate, and has an average absolute error of 10%.

In the present work, dispersed phase HOLDUPs have been measured in a Hanson mixer-settler extraction pilot plant with seven stages for two different liquid-liquid systems. The effects of agitation speed, dispersed and continuous phase flow rates have been investigated under a variety of operating conditions. Dispersed phase axial HOLDUP profiles, determined by a sampling method, showed a strong nonuniformity. The results also showed that the dispersed phase HOLDUP changes largely with the direction of mass transfer. Finally, an empirical correlation in terms of physical properties of liquid systems and operating variables was proposed to predict the HOLDUP and good agreement between experimental data and calculated values of HOLDUP was obtained.

In this study, effect of ethanol and anionic, cationic and non-ionic surfactants on circulation velocity, mixing time and GAS HOLDUP in a three phase (water and alcohol-air-PVC particles) concentric draft tube airlift reactor have been investigated. In this experiments, Changing of GAS velocity, liquid level and solid loading was investigated. Airlift reactor with height, internal tube diameter, outer tube diameter 173, 5 and 8 centimeters respectively, was made of glass. In GAS-liquid-solid systems, with increasing GAS velocity, GAS HOLDUP in riser and liquid velocity increases. The results show that GAS HOLDUP increases, surface tension and liquid circulation velocity decreases in the presence of alcohol, furthermore the results illustrate that non-ionic surfactant has greatest impact in proportion with cationic surfactant and ionic surfactant on GAS HOLDUP. In this study, the equation has been proposed for liquid velocity and GAS HOLDUP and mixing time.

Background and Objective: In This study the impacts of operating conditions such as aeration rate, the downcomer-to-riser cross-sectional area ratio (Ad/Ar), and liquid phase properties on the hydrodynamics and volumetric mass transfer coefficient in three-phase airlift reactors was investigated. Method: Experiments were conducted in external loop air-lift reactor with downcomer to riser cross-sectional area ratio (AD/AR=0. 14) and internal air-lift reactors with downcomer to riser cross-sectional area ratios 0. 36 and 1. Air and Water were used as GAS and liquid phases, respectively and activated sludge is used as the solid phase. Findings: The liquid circulation velocity, GAS HOLDUP and mass transfer coefficient increased with an increase in the superficial GAS velocity, decrease the sludge concentration and decrease downcomer to riser cross-sectional area ratio. The maximum amount of GAS hold up, 0. 178 in external air-lift reactor with 1%(w/w) activated sludge in superficial GAS velocity 0. 24(m/s) was observed. A model to predict the effect of activated sludge concentration, the superficial GAS velocity and the downcomer-to-riser cross-sectional area ratio on the mass transfer activated sludge airlift reactors provided which with the experimental results are in good agreement. Discussion and Conclusion: The evaluation of internal and external reactors performance at different concentration and superficial GAS velocity show that the air-lift reactor with external loop has better performance in comparison with internal airlift reactors.