Abstract
The effect of liquid viscosity on slug flow in a 50 mm diameter bubble column was investigated experimentally using air-silicone oil as operating fluid with silicone oil of viscosities 5, 100, 1000 and 5000 mPa.s. Data was collected using Electrical Capacitance Tomography (ECT), a non-intrusive advanced instrumentation measuring technique and the high Speed Video Camera, through which the slug parameters such as length of Taylor bubbles and liquid slug, void fraction in Taylor bubbles and liquid slug, slug frequency, film thickness and pressure gradient in the slug, were measured and analyzed. The analysis was done using the void fraction time series, probability density function and power spectral density plots. Superficial gas velocities of 0.02≤Ugs ≤0.361 m/s were used in the experiment. It was also observed that as viscosity increases, slug frequency, structure velocity, length of liquid slug, void fraction in liquid slug and void fraction in Taylor bubbles decreases; while the length of Taylor bubble, film thickness and pressure gradient in the slug increases.
Highlights
Slug flow is encountered in the heat and mass transfer between gas and liquid in chemical reactors, most especially when it involves highly viscous liquid in either small or large diameter bubble columns
The film liquid holdup was said to be directly proportional to the liquid viscosity due to an increase in the interfacial and wall shear forces on the liquid film. [2] from the empirical correlation developed for slug liquid holdup as a function of liquid viscosity explained that the slug liquid holdup is directly proportional to the liquid viscosity [27] and [15] reported an increase in slug frequency with increasing liquid viscosity for which they developed an empirical slug flow correlation
The slug cross-sectional area increases with an increase in the frictional and gravitational forces impacting on the slug
Summary
Slug flow is encountered in the heat and mass transfer between gas and liquid in chemical reactors, most especially when it involves highly viscous liquid in either small or large diameter bubble columns. The use of highly viscous liquid in small diameter bubble columns results in slug flow which involves the appearance of typically bullet-shaped large pockets of gas called Taylor bubbles which occupy a large part of the cross-section of the column. Several investigators have carried out different studies on slug, few studies were found on the effect of liquid viscosity on slug flow. Smaller wall effects are observed in larger diameter columns [16], [19], [20]
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