Hydrodynamic study of anadjustableheightpacked column operating

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –

6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

461

HYDRODYNAMIC STUDY OF AN ADJUSTABLE HEIGHT PACKED

COLUMN OPERATING ON THE PRINCIPLE OF AN

AIR LIFT PUMP

Adel OUESLATI 1 *

, Ahmed HANNACHI2, Mohamed EL MAAOUI

3

1College of technology, Department of Chemical engineering, Mogran, 6227,Zaghouan –

Tunisia 2National school of Engineers, Gabes, Department of chemical engineering, Omar ibn El

khattab, Zrig, 6072- Tunisia 3Faculty of sciences of Tunis, Department of chemistry, Elmanar 1002- Tunisia

ABSTRACT

A setup consisting of a glass column packed with calibrated glass rings has been

achieved. It operates on the principle of an air lift pump. It was designed for the best contact

between air and water. Performances of this system were determined by measuring the

displaced water flow rates for different submersion depths and various air flow rates. We

studied the pressure drop versus the immersion depth in the column. The results show that the

pressure loss is described by a second order polynomial equation. Efficiency was calculated

for different conditions. The study shows that the proposed system can be set easily, has low

power consumption, provides a good mix between phases and is very important for many

applications where heat and mass transfer are involved.

Keywords: air lift pump, porous media, packed column, efficiency

1. INTRODUCTION

The pumping system of water by air lift consists of the injection of compressed air at

the base of a pipe in order to drive the liquid therein. The only source of energy, used for

pumping, is compressed air. A two-phase mixture is water-air, of lower density than the

surrounding liquid. Upward movement is initiated, and causing a stream of water.

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING

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ISSN 0976 – 6340 (Print)

ISSN 0976 – 6359 (Online)

Volume 4, Issue 2, March - April (2013), pp. 461-478

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462

Air lift pumps are widely used in aquaculture (Parker et al., 1987 [1)), in bioreactors

(Chisti V., G. Trystam [2], 1992) in geothermal wells (Reley DJ, Parker GJ [3], 1982) in

underwater exploration (JL Mero [4]; Stenning and Martin [5], 1968), the extraction of

sludge in wastewater treatment (Casey TJ [6], 1992 and storck [7], 1975).

Pumping systems air lift type are considered effective for low head conditions compared to

centrifugal pumps and other pumps (Lee, 1997 [8]; Kumar [9], 2003 and Oh [10], 2000).

However, this efficiency was defined by Nickelin [11], (1963) and used by Rienemann [12],

(1987) is given by the following relationship:

η � ρ��

(1)

With:

ρ�: Density of the liquid, g: Acceleration due to gravity, Q, Q�: volume flow rates of the

liquid displaced and gas respectively, Z: Pressure head (m), P�, P�: Gas pressures

respectively at the top and bottom of the column.

Here we see that for values of QG and P0 data, QL and P1 will depend on factors that

influence the hydrodynamics of the system. The hydrodynamic in a gas-liquid contactor is

very complex. Characterization begins with the determination of gas flow regimes. Several

authors have defined flow regimes co-updraft gas. Five regimes, two-phase flow water-air

vertical co-current, observed by Roumy [13] (1969): Bubbles, separate dense bed of bubbles,

slugs, annular and churn.In general, the transition from one regime to the other takes place by

varying one or both of air flows and water. But in the case of an air lift, the gas flow rate and

the initial height of the liquid, in the riser, that secure the flow rate of the circulating liquid

and the flow regime.

The pressure drop (P0 - P1) resulting mainly to gravity and viscous forces. They

depend closely on speeds of fluids and therefore, they are dependent on the flow regime.

Correlations for determining the pressure drop have been established by Govier GW and Aziz

A. [14] (1972), Govier and Radford,[15] (1957) for bubbles regimes, by Friedel [16],

(1979) in the case of slug regime and by kern [17], (1975) if the flow is like churn and

annular.

The gas hold up is the ratio of the volume of gas contained in the mixture biphasic on

the useful volume of the column. It is the sum of the dynamic gaseous fraction and the static

gaseous fraction.

Experiments carried out by several authors (Wallis (1969) [18], Nicklin [19] (1962))

showed that the value of gas holdup varies with superficial gas velocities.

It has an effect on the flow rate of the liquid and interfacial area (Merchuk [20],

1981).

For flow rates of gas and liquid, gas retention is variable from one point to another in

the column.

It also depends on the design of the closed loop air lift system including the

connections between the riser pipe and tube down comer (Merchuk [21], 1994). The author

reports elucidated the effect of sections of the riser and the down comer of the gas holdup

value. Nakoryakov [22] (1986), Rienemann [12] (1987) and Merchuk [21] (1994) showed

that the gas holdup depends on the diameter risers and the effects of viscosity, surface tension

and Reynolds number . The authors confirmed that if the tube diameter is much less than 6

mm and if the gas flow is cut, surface tension prevents the rise of gas bubbles.



463

Air lift pumps that we present above are exclusively formed by a vertical tube in

which there is water at a given height and air injection at the base. Our work is to use an air

lift system wherein the tube is filled with packing. Although packed columns are very well

known, the combination air lift and packing has not been addressed. Merchuk [21], (1994)

studied the air lift bioreactors unlined but improved turbulence by design. There are other

researches achieved a packed column reactor where liquid and gas are sent by two different

pumps (Barrios QEM [23], 1987; Sicardi S., G. Baldi, V. Specchia, I. Mazzarino [24], 1984,

A. LARA Marquez [25], 1994).

The packed column is used for the mixing and intimate contact between the phases.

The rest of the studies, which are related to our work, concerned to conventional

packed columns in which we seek to characterize the concurrent up flow of air and water.

The parameters involved are flow regimes, gas and liquid hold up, liquid and gas flow rates

and pressure drop. Flow regimes are studied by JL Turpin, R. L. Huntington, [26], (1967);

Y. Sato et al. [27], (1974), Nakamura et al. [28], (1978);, Barrios [23], (1987) and Lara et al.

[29], (1992). The studies have shown that the gas flow depends on flow regimes and fluid

characteristics of packing. Since the regime depends on the characteristics of solids, so we

cannot make flow regimes maps similar to that of a biphasic system.

On the gas holdup, studies by Moustiri [30], (2002); Therning [31], (2001), Lara

Marquez [29], (1992), Abraham [32], (1990) and Barrios [23], (1987) showed that the

overall retention of the gas increases as a function of the superficial velocity gas and

decreases with that of the liquid without offering an explanation of the effect of solid packing

on the gas holdup. The pressures drop in a packed column where the flow is co-current

upward can be described by the modified formula Ergun whatever regime (Maldonado JG, G.

Hebrard, D. Bastoul, Roustan, JL Westrelin S. Baig, [33], 2004). The same authors have

defined sleep velocity and their effects on the mass transfer.

This work is a study of co-flow updraft of a water-air mixture in a packed column

vertical operating on the principle of an air lift pump. The column is filled with glass rings.

The water is flowing in a closed loop. In addition to its large surface area, the glass rings are

characterized by a high void fraction which maintains a low pressure drop. Possible

applications are expected in the field of air humidification or stripping. The tests are

performed in ambient conditions. Only two parameters are adjustable: the gas flow rate and

the initial height of the liquid in the riser. Water flow generated, the gas holdup, pressure

drop and pump efficiency are determined to evaluate the performance of assembly.

According to the trends observed in the experimental study a physical interpretation is

proposed.

2. MATERIALS AND METHODS

2.1. The experimental setup Fig. 1 shows a schematic diagram of the setup. The system main components are:

evaporator (1), down comer (2), water heater (3), cyclone (4), compressor (5), water flow

meter (6), water make up Tank (7), air heater (8), air flow meter (9), temperature control (10),

swirl chamber (11), vapor condensers (12) and (13), Inlet cooling water (14), outlet cooling

water (15), pure water Tank (16), water level control (17), Temperature sensor (18), Relative

Humidity (HR) sensor (19) and pressure manometers.



464

The experiments were performed on a vertical cylindrical column made up in three

glass tubes 0.072 m diameter and 0.4 m length. The total height of the column and the

packed bed are 1.2 m and 1.0 m respectively. The characteristics of the solid packing are

shown in Table 1. The column is provided with equidistant pressure sensors in order to

measure the local pressure at different heights. Four polypropylene disc diffusers, with 67

circular pores of 5 mm each, are arranged at the ends of the glass tubes. They have a

double role: first they change the fluid flow direction, second they prevent the exit of

solid packing out of tube. Only one air jet nozzle is used in the experiments. It has a

diameter of 3 mm.

At the input of the column, a swirl chamber, stainless steel, is designed for the

injection of water and air. At a height equal to 1.02 m of the column, water is recycled

through a down comer and the air continues its path to the cyclone and condensers.

Water droplets separated at the cyclone are routed to the swirl chamber. A make-up tank

of water is placed to keep a constant liquid level in the down comer.

The water flow rate is measured by an orifice, with piezometers, placed between

the down comer and the riser. His uncertainty is less than 5%.

The compressor used of 2 kW power, Michelin type and 25 liters of tank, provided

with a flow controller valve. The air flow meter is air float type; brand Tubux whose

measuring range is between 0 and 25 m3 / h and the uncertainty of 4%.

The setup is designed in a manner that the amount of water evaporated will be

replaced, automatically, by the same amount of liquid water issued from the tank (7).

The riser will be used as an evaporator chamber. It is insulated by a transparent

polyethylene layers. The airflow humidified by passing through water level in evaporator

chamber then leaves from the outlet pipe in the direction of condensers. The water level

in the evaporator chamber is controlled by the level of water make up tank (7) and an

electric heater (3) of 2 kW power. The inlet water flow rate in the evaporator is measured

by a calibrated orifice (6).

The physical properties of the packing particles are given in table.1.

Table 1: Physical characteristics of the packing particles

Type of packing particles Glass rings

Density : ρS 2.187 (kg/m3)

Average diameter: dp 0.008 (m)

Averagelength : lp 0.008 (m)

fixed bed porosity: ε 77.3

Form Factor: φ 0.681



465

Fig. 1. Schematic diagram of the set up

Fig.1: Schematic diagram of the experimental setup: evaporator (1), down comer (2),

water heater (3), cyclone (4), compressor (5), water flow meter (6), water make up Tank (7),

air heater (8), air flow meter (9), temperature control (10), swirl chamber (11), vapor

condensers (12) and (13), Inlet cooling water (14), outlet cooling water (15), pure water Tank

(16), water level control (17), Temperature sensor (18), Relative Humidity (HR) sensor (19).

The submersion ratio Sr is defined by this expression:

��

(2)

Where:

Z s: submerged depth (initial liquid height), The design for air lift pumps has typically been

based on data derived from performances within the limits of S r (40% - 90%) (CHO Nam –

Cheol, Hwang in ju, Lee chae-Moon, Park jung-won [34]). The total head, L is given by the

following equation:

Z s + Z L = L (3)

For this study, the total head is 1.02 m, so Z s, can any value between 0.4 and 0.9 m.



466

2.2. Measuring the pressure drop To measure the pressure loss due to the fluid flow between the ends of packed

column, we used a differential manometer connected to the tail and the head of the column.

Another differential pressure gauge is intended for measuring the pressure at the head of the

column with respect to that of the atmosphere. The measurement error by differential

manometer is equal to �2 mm.

2.3. Measuring the global gas hold up

The gas hold up is defined as the volume occupied by gas in the packed column

crossed by a diphasic mixture in continuous operation. It called also void fraction. It is

measured by set a level of liquid in the packed column, which corresponds to a volume V0 of

the liquid. Then, we inject a gas flow rate. Once the steady state is reached, flows into and

from the packed column are cut by closing the corresponding valves. The new liquid volume

V1 in the packed column is noted. The void fraction is then:

� � !� "!!� (4)

3. RESULTS AND DISCUSSION

3.1. Average water flow rate

The results of measurements are plotted in Fig. 2.

Fig. 2. Effect of the Gas flow rate on the water flow rate for many submersion ratios

The examination of Fig.2 shows that there is a jump, in all the curves. This is

attributed to movement of the packing which is subject only to his weight. Under the effect of

flow, the mixture of gas and liquid induce a movement of packing, the void fraction increases

and the liquid flow rate increases also. Unless the presence of the perforated discs all the

packing would be ejected.

This jump, which has a great influence on the liquid flow rate and pumping efficiency,

becomes more important if submersion ratio, Sr, is also important.



467

Fig. 3. Liquid flow rate is a function of submersion ratio Sr

Fig.3 is a graphical representation of liquid flow rate as submergence ratio. We find

that the liquid flow rate increases with the gas flow. This curve confirms the relationship

between the liquid flow rate and the submergence ratio is linear when QG= 1.265 Nm3/h. But,

when the gas flow rate increases, the relationship becomes nonlinear. Some authors like to

show the effect of the superficial gas velocity on the superficial liquid velocity.

In order to find a model that includes the operating parameters (gas and liquid flow rates,

submergence ratios) with the characteristics of the system (tube section, etc.), we represented

the flow rate ratio (QG / QL) based on liquid flow rate QL for different submersion ratios (Fig.

4a). We got a parabolic relation in the range of liquid flow rates (0-105 L.h-1

).

(a) This study (b) D. Moran study [35]

Fig. 4. Effect of Liquid flow rate on the Gas liquid flow rate ratio

Outside this range, the curve is no longer parabolic, due to change of void fraction in

the bed. It is worthy to say that the curves of fig. (4a) of this study are similar to that obtained

by D. Moran [35] (Fig. 4b) with other conditions and type of air lift pump.



468

Fig.5a. Effect of mass gas flow rate on the mass liquid flow rate (Our results and there obtained

by Khalil [36] and Parker[1]))

Fig.5b. Effect of mass gas flow rate on the mass liquid-gas ratios

The fig. 5a shows a comparison between results of this study with the analogous

results obtained by other authors (parker [1] and Khalil [36]).The latters were related to other

air lift pumps and other conditions, in which there is no packing, but in a same submergence

ration (S r = 0.55). We observe the same trends. In our case, it is obvious to note that packing

causes the decrease of the liquid flow rate.



469

Parker [1] considered the pumping efficiency can be described by liquid- gas mass

ratio versus mass gas flow rate. He obtained a parabolic curve similar to that obtained in this

study (Fig. 5b). The same author recommended plotting a dimensionless liquid flow rate [QL

/ (Ar*(2*g*Zs) ½

)] versus gas-liquid flow rate ratios (QG / QL). With, Ar is riser section, g is

the gravity and Z s is the submersion depth.

Fig. 6.Effect of gas-liquid flow rate ratios on the dimensionless liquid flow rate

The curves, obtained in (fig. 6), show that a model can describe the relation between

the operating parameters and setup characteristics. This model has been given by the

following expression:

# � $. &"' (5)

Where:

# � (�)*+,-��

(6)

& � (.(�

(7)

386.04 4 $ 4 701.4 (8)

1.314 4 7 4 1.618 (9)



470

Table 2, gives the values of α and β for each submerged ratio value.

Table 2: fitted equation for each submerged ratio

S r(�

)*89,8-8��:/<� =9(.(�): Fitted equation R

2

0.5 (�

)*89,8-8��:/<� 386.04 8 �(.(��

"�.>�?

0.9656

0.6 (�

)*89,8-8��:/<� 701.4 8 �(.(��

"�.@�A

0.9791

0.7 (�

)*89,8-8��:/<� 435.9 8 �(.(��

"�.DD�

0.9806

3.2. Pressure drop across the height of the fixed bed Experiments to measure the pressure drop through the bed were carried out for

different initial liquid heights using a differential manometer. The scope is to determine the

effect of gas flow rate, submerged depth and bed porosity on pressure drop.

Fig. 7.Effect of gas flow rate en drop pressure for dry packing

Fig. 7 shows the effect of air flow rate and the dry packing on the pressure drop. The

tests are achieved in ordinary conditions. The obtained results can be fitted by a linear

equation indicated in fig. 7. The pressure drop increases linearly with the gas flow rate and

his maximum value is less than 450 Pa in the test conditions.



471

(a) (b) (c)

Fig. 8.Effect of air flow rate, submersion ratio and the fluid velocity on the pressure drop.

Fig. 8a shows the experimental curves relating the pressure drop per unit bed height

versus air flow rates for different submersion depth. The analysis of the results shows the

influence of the submerged depth and the gas flow rate on the pressure drop.

Fig. 8b shows the variation of pressure drop per unit height of packed column,

against the submersion depth for different gas flows. The curves obtained have a positive

slope. For QG = 0.758; 1.265 and 1.517 Nm3/h all the curves are linear and in agreement

with the fact that when the liquid height, Zs, (i.e. Sr) increases, air flow encounter more

difficulties to cross the packed column. So, ∆P increases.

The lines are classified according to increasing QG. This is consistent with the fact that ∆P is

of the form:

∆F � =. GH . IH,. J9�"K:LMN

KL O �PLMN QR

(10)

(Leva [37], 1959)) where, GH and IH are the density and the superficial velocity of the fluid

mixture respectively. Φ and ST are the shape factor and diameter of packing respectively. n

is a constant.

f is the friction factor, which is related to Reynolds number, Re, by the following equation:

= � UVWN (11)

Where, b is constant and the Reynolds criterion based on grain size is:

XY � IHGHST /µH (12)

µf is the fluid viscosity (pa /s).



472

For QG = 2.023 Nm3/h a change in the slope is observed at �� Z 0.6. This phenomenon could

be attributed to the displacement of the packing rings when they are submitted to a high gas

velocity. The new curve branch is linear and shows a significant increase in the slope.

We see, in a first approximation, that:

- When the submersion ratio is very important, ∆P has approximately a parabolic form.

- For a lower value of Sr (Sr = 0.6) the parabolic form is more flat.

- For Sr more lower, (Sr = 0.5), we have a parabolic branch very close to a linear form.

Considering that a parable is described by the following formula: � [. &, \ ]. & \ ^ .

We know that the parable is more and more flat when the coefficient, a, is smaller and

smaller.

To a fixed liquid immersion depth, the pressure drop increases with increasing gas flow,

which can be attributed to the growth of the water flow. These experiments show the

importance of the degradation of energy by friction. The pressure drop is given by the

expression of Ergun [38], (1952):

∆_àbc

� d 9�"K:<KL

µe9ΦQf:<

IH \ g �"KKL

he9ΦQf:

IH, (13)

This equation can be written as follows:

∆_àbc

� i�.µH . IH \ i,. GH . IH, (14)

With:

i� � d 9�"K:<KL

�9ΦQf:<

(15)

And

i, � g �"KKL

�9ΦQf:

(16)

Fluid velocity:

Uf = (UG + UL) = (QG + QL) / Ar (17)

According to this equation, the pressure drop increases with the superficial liquid velocity UL.

Trends illustrated in Fig. 8c are described by the second order polynomial equation. We note

that the viscosity µf and density, ρf depend on the temperature, so that the value of the

pressure loss depend on the thermodynamic conditions of the measurements. Fortunately, all

the experimental values in this work were obtained at constant temperature (27°C). It should

be noted that each submersion ratio corresponds to a hydrostatic pressure, Fjk, which is equal

to :

Fjk � G�. l. mn (18)

Where:

G�: Liquid density (kg. m-3

),l:Gravity (m. s-2),



473

Thus the air must have a pressure greater than (Fjk \ ∆F) for flowing in the packed

column. Below this value, the gas does not pass through the packed column; therefore we

cannot talk about pressure loss. So, the curves of pressure drop versus fluid velocity for

different submersion ratios (Sr= 0.5; Sr=0.6 and Sr=0.7) do not go through the origin. They

have the following equations in the following table 3:

Table 3: fitted pressure drop equation for each submerged ratio

Sr Fitted Pressure drop equation

R2

0.5 ∆_`pbc

� 0 8 IH, \ 5326.7 8 IH \ 1138.7

0.9696

0.6 ∆_`pbc

� 117966 8 IH, r 10601 8 IH \ 1837.4

0.9817

0.7 ∆_`pbc

� 214499 8 IH, r 18464 8 IH \ 2214.2

0.9863

0 (dry packing) ∆_`pbc

� 0 8 IH, \ 1575.6 8 IH \ 41.43

0.9384

It is instructive to say that we can find easily the effect of liquid flow rate on the

pressure drop. For a submersion depth of 60cm and for a gas flow rate of 2.023 Nm3/h, the

characteristics of the bed change due to the porosity variation explained above, the pressure

will increase rapidly. A jump is observed for submersion depth of 60cm and 2.023 Nm3/h of

gas flow rate (fig. 8a) the same jump is observed at a point having the coordinates 70 cm as

submergence depth and 1.5 Nm3/h as gas flow rate (fig. 8b). So the jump depends on the gas

flow rate and the submergence depth.

3.3. Gas hold up The global gas hold up profiles obtained in the fixed bed at different gas flow rates

and liquid heights submersions were determined. The same tendencies are observed at all

submersion ratios (Fig. 9).

Fig. 9. Effect of gas velocity on the gas holdup



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Whatever, we can note that global gas holdup increases with increasing gas flow rates

and decreases with increased liquid flow rates. These variations have been already pointed

out by Heilman [39], (1968); Achawal [40], (1976); Barrios [23], (1987);Lara Marquez [29],

(1992) and Gillot [41], (2005).

The global gas hold up is the sum of the dynamic and static gas fractions. The

dynamic gas fraction is the volume of gas in the packed column which is renewed

continuously by the inlet gas throughput. But the static gas fraction corresponds to the

remaining gas in the packed column when the gas flow is cut off. It depends on the

characteristics of the fixed bed such as porosity, shape and nature of the packing (Maldonado

[33], 2005; Tung et al. [42], 1988).

The decrease of the global gas holdup with increasing of submersion ratio is attributed

to the decrease in the drag force.

3.4. The slip velocity

The slip velocities are calculated from the following equation:

s � t.K. rt�

�"K."K� (19)

Fig.10a. Effect of gas velocity on the Fig. 10b.Effect of gas velocity on the

Slip velocity (This study) Slip velocity (Maldonado [33] study)

The fig.10a shows the increase of the slip velocities with the superficial gas velocities.

Moreover, it appears that the high values of slip velocities are obtained with low submersion

ratios. So, the slip velocities increase with decreasing contact area. A comparison of this

study with that achieved by Maldonado [33] (fig. 10b), we conclude that the slip velocity,

obtained in this, is greater than that obtained by Maldonado [33]. This greatness is attributed

to the importance of gas hold up in our case, which is related to the high gas velocities and

glass ring as packing used in this study.



475

3.5. Efficiency of the air lift pump The term air lift pump efficiency was presented by equation (1). It is used by several

authors for system pumping evaluation. Fig. 11a shows that the efficiency of the air lift pump

increases with increasing gas flow rate up to a certain value where it becomes almost constant

and decreases after. The submergence ratio (Sr) effect is observed in this curve. The

efficiency decreases with the increase of submersion ratio.

(a) (b)

Fig. 11. Effect of the air flow rate on the efficiency of the air lift pump

The comparison of this study with that achieved by Khalil [36] shows easily the same curves

trends; even the two air lift pumps and the operating conditions are different (fig. 11b). So, it

is important to underline the gas energy loss caused by liquid flow rate, packing and the

connection between the riser and the down comer. Merchuk [21] showed that if, Ad and

Ar are the sections of down comer and riser respectively, the decrease of the ratio (Ad / Ar)

have a negative effect on the gas holdup but also a negative effect on the pumping liquid

efficiency. However, it should be interesting to announce that the setup is designed not for

very high pumping liquid flow rates but for high heat and mass transfer efficiency.

Consequently, liquid flow rates recorded, in the experimental study, are very high for many

applications.

4. CONCLUSIONS

In this study we determined, under ambient conditions: atmospheric pressure and

temperature of 27°C, the effect of immersion depth and the gas flow on the liquid flow rate.

Air flow rate have an important effect on the liquid flow. At a given submerged ratio, liquid

flow rate depends on gas flow rate, bed porosity and system design. When gas flow rate

increases, then liquid flow rate increases also. Besides, the submerged ratios increase the

liquid flow rate increase also. In the range of operating conditions tested the liquid flow rate

decreases with increasing of gas -liquid flow rate ratios. We found that liquid flow become

high enough when immersion depth is greater than 40%. Below this value, the pumping of

water in a granular medium by the air is impossible.



476

It is observed that the pressure drop per meter of packed bed increases with increasing

gas flow rate. It increases more intensively with the increase of submerged ratio. It can be

described by a second order polynomial equation. Average gas holdup and slip velocity

increase with superficial gas velocity but decreases with an increase of submerged ratio and

liquid velocity.

Finally this study shows that the pump efficiency increases with increasing gas flow

rate up to a maximum is reached. Then it decreases regardless on the gas flow. The packing

presence is really an obstacle to liquid flow. A model giving the liquid flow rate for a given

gas flow rate and for submergence ratio range, between 0.5 and 0.7, is proposed. As a

conclusion we can say that the studied set up is very interesting and may constitute the base

of several useful applications.

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