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is that based on the elastic theory.
Studies on the drag reduction technologies, percentage drag reduc-
tion and friction factor are of great interest from the industrial point
of view. In particular, drag reduction studies on packed columns
are very much useful to reduce mechanical energy losses, which
reduces the cost associated with transport of fluids like pumping,
thus reducing the overall operating costs. The knowledge of flow
regimes in a packed bed column, for a desired set of flow condi-
tions, liquid properties viz., viscosity, density and surface tension and
packing geometry, is essential for the proper design and successful
scale-up of packed columns. The flow regimes in a packed bed down
flow column have a significant influence on the design variables viz.,
pressure drop, liquid holdup, interfacial area and mass transfer coeffi-
cients. The mixing characteristics of the contacting phases and theirtransport properties in the column are more dependent on the op-
erating flow regime in packed bed column which largely depends
on the mass flow rate of gas-liquid phases, size and shape of the
particles, bed voidage and physical properties of liquids.
Several studies have been conducted to determine the extent of
drag reduction for different polymers in different systems. The de-
pendency of drag reduction on various factors, including polymer
molecular weight, polymer concentration and temperature, have
been investigated by many authors [5-8]. Based on the literature
review, it was found that the effect of xanthan gum as drag reducing
agent in co-current air-water down flow through a packed column
has not been reported till date. For the present work, it is proposed
to use xanthan gum as drag reducing agent and to study its effect
on flow regime transition, friction factor and drag reduction in co-
current air-water down flow through a packed column.
EXPERIMENTAL SETUP
AND COLUMN OPERATION
1. Experimental Setup
The experimental setup consists of a Perspex column of 1.9 m
in height and 0.115 m internal diameter. Fig. 1 shows the schematic
representation of the packed column used for the present work. The
column dimensions and particle dimensions are given in Table 1.
At the top of the packed column a gas-liquid distributor was placed
to ensure the regular and uniform distribution of air-liquid mixture
inside the testing section. In the top gas-liquid distributor, liquid
inlet was connected axially through solenoid valve and gas inlet was
connected horizontally. A separate gas-liquid separator was pro-
vided at the bottom of the column to have proper separation of two different phases, where the separated liquids were re-circulated back
to the column. The flow rates of two different phases (gas and Liquid)
were measured using a calibrated rotameter. Liquid was pumped
by a centrifugal pump and the flow rates were controlled with a gate
valve, and compressed air was pumped into the column through
the surge tank and then through the calibrated rotameter.
2.Measurement of Liquid Properties
The liquids used in this present work were water and water+xan-
than gum solution of different concentration (300, 400, 600 and 800
ppm). The mixture behaves as a low shear thinning solution. Sine
the liquid system used in this study exhibits a thyrotrophic nature,
the basic properties like density and viscosity were measured using
drop weight method (specific gravity bottle) and Haake viscometer
(model VT 181), respectively, where the shear rate for various applied
shear stresses was measured. The flow consistency index ‘k’ and
flow behavior index ‘n’ were evaluated using the power law model
which is given in Table 2.