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MECH-PHD-05-802

Characterisation of slug flow in Horizontal channelsSurendra kumar. A. M., Ph.D, 05, 224 pp.

Department of Mechanical Engineering

Indian Institute of Technology Bombay, Powai, Mumbai 400 076.

Supervisor(s): Kannan N. Iyer

Slug flow is encountered in many practical situations, where it could damage

equipment due to the characteristic pressure rise associated with it. This could

induce shock loading on any equipment in which it occurs. In a pressure tube nucleareactor, during accident conditions, the fuel rod bundles can get overheated due to

onset of stratification. In such situations, onset of slug flow would enhance heat

transfer and promote cooling. Therefore, an accurate prediction of the onset of slug

flow regime and its characteristics is of great practical importance. Experimental

studies have been carried out for an airwater two phase flow system in two acrylic

pipes of diameters 19 mm and 44 mm ID (Inner Diameter) to obtain the different

characteristics of horizontal slug flow. In addition, experiments have also been carried

out in an annulus formed by inserting an acrylic pipe of diameter 30 mm OD (Outer

Diameter) into a pipe of diameter 44 mm ID. The characteristics studied in this work

include, frequency of slugging, translation velocity, length of slug and pressure drop.

To characterize the first three features, a wire mesh probe was designed and

fabricated. This probe consists of two sets of 4 wires separated by a distance of 2

mm. It identifies the presence of liquid or gas by measuring the fluid conductance.

The cross correlation between signals from the two wire mesh probes placed at

distance of 1m is used to find translation velocity of the slug. To unify the results a

correlation is proposed to relate the ratio of translation velocity ((Vt) to slug velocity

(Vs)) in terms of slug Reynolds number. The frequency of slugging is found bysubjecting the signals from a wire mesh probe to FFT analysis. Using the liquid

wetted time and slug translation velocity, the length of the slug is estimated. The

results obtained in the current study compare well with the published data available

in the literature. The frequency results agree well with the Taitel and Dukler model.

Similarly the pressure drop agrees well with Fan and Hanratty model. To unify the

entire results, correlations have been worked out for dimensionless length L/D, non-

dimensional frequency and pressure drop (two-phase multiplier) as functions of four

non-dimensional parameters, X, Z, FL, and FG,. The obtained correlations predict the

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present experimental data and other data in the literature for circular pipes within

20\%. Analysis was also extended to predict the results obtained from the annulus

pipe and it showed good agreement. These results were also correlated. Key Words

Slug flow, Wire mesh probe, Slug frequency, Slug length, Slug pressure drop.