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3. Column Operation
3-1.Mode of Operation of Column
The column was operated under co-current down flow mode by
allowing liquid and gas through the gas-liquid distributor located at
the top of the column. Eight different manometer tapings were used
in the column to measure the pressure drop at various positions across
the length of the column. During operation the pressure drop was
measured by a U-tube manometer for different phase flow rates.
Initially, the experiments were carried out using an air-water sys-
tem without DRA, and then it was extended with the addition of
suitable xanthan gum (DRA) of different concentrations ranging
from 300 to 800 ppm and air-Newtonian liquid systems (glycerol,
ethylene glycol of different concentration) (JagadeeshBabu et al.
[9]). Apart from the pressure drop data, another important hydro-
dynamic variable, flow regime was measured by visual method and
compared with pressure drop method.
3-2.Measurement of Two Phase Friction Factor and Drag Reduc-
tion
A simple U-tube mercury manometer was used to measure the
pressure drop across the testing section. Both ends of the manome-
ter were initially connected to a gas-liquid separator and then con-nected to the pressure tapings. Before taking readings from the ma-
nometer, care was taken to ensure that the limb of the manometer
was filled with the same column liquid and that the limb was free
from any gas bubbles that might interfere with the manometer read-
ings. From the manometer reading the two phase pressure drop was
measured. The drag reduction DR was calculated as below:
% DR=(∆Pw−∆PDRA)×100/∆Pw (1)
RESULTS AND DISCUSSION
The knowledge of flow patterns plays a major role in determin-
ing the degree of drag generated in the packing, where the flow pat-
tern purely depends on the fundamental variables like liquid prop-
erties such as viscosity, density and surface tension and packing
geometry.
1. Flow Regimes and Flow Regimes Transition
Knowledge of the flow regime plays a vital role in the design of
packed bed down-flow reactor. These flow patterns give a basic
idea about bubble dynamics during gas-liquid interactions, which
occurs between the stationary solid bed during column operation.
The flow regime and flow regime transition plays a significant role
in determining the hydrodynamic variables like pressure drop and
corresponding phase holdup. In this present study, water is used as
the liquid system and air is used as the gas medium. In general, flow
patterns can be measured either by visual observation or by pres-
sure drop method.
In this present study, visual observation was used to identify dif-
ferent flow regimes, and further it was confirmed by using the pres-
sure drop method. Initially, the column was operated at low gas and
liquid flow rate, where the liquid starts to trickle over the particle
and the gas flows through the available pores. In this flow regime
gas is considered as a continuous phase and liquid as discontinu-
ous phase. Furthermore, with a moderate increase in the gas flow
at constant liquid flow rate and vice versa, the drag force between
the gas-liquid interface increases, which leads to the accumulation
of small liquid droplets as discontinuous liquid rich zone traveling
downward causing a pulse regime. At high gas-liquid mass flow
rate, the gas becomes discontinuous and liquid becomes continu-
ous leading to dispersed bubble flow regime.
Visually observed flow regime data were plotted to identify the
flow regime boundary between the three different flow patterns.
Liquid mass velocity ‘L’ in kg/m2
s as abscissa is plotted against gas
mass velocity ‘G’ in kg/m2