hasil translate-pengaruh nozzle terhadap kinerja kolom gelembung pancaran (t)

8/11/2019 HASIL TRANSLATE-Pengaruh Nozzle Terhadap Kinerja Kolom Gelembung Pancaran (T)

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THE EFFECT OF THE NOZZLE ON THE HYDRODYNAMIC OF JET

BUBBLE COLUMN PERFORMANCE

Abstract . Jet bubble column is one of gas-liquid mass transfer means. The purposeof this research is to study the effects of nozzle on the hydrodynamic; the depth ofbubble penetration, gas holdup, and gas entrainment in the jet bubble column.

Process variables study about the followings; fluid volumetric flow rate (10-50 L /min), the size of the nozzle diameter (8 to 12.7 mm), and height of nozzle (12.5-25cm). The results showed that the smaller nozzle diameter and fluid volumetric flowrate generate increasingly large gas entrainment, gas holdup, and the depth ofbubbles penetration become larger.

Key words : Jet bubble column, gas entrainment, depth of bubble penetration.

1. INTRODUCTION

The process of mass transfer from the gas phase to the liquid phase wasgenerally encountered in the industry, such as the chemical and petrochemicalindustries. In this case, the jet bubble column that serves as means of contact betweenthe gas-liquid phases is widely encountered in the process of natural aeration and

industrial systems, including chemical plants, mineral processing, and wastewatertreatment (Liu, et al., 1998).The working principle of this device is quite simple; the gas phase will be

inhaled down through a stagnant fluid hole shaped like a trumpet, which is caused bythe liquid collision-jets speed. The collision resulted the rupture of fluid film layer, sothat the gases will be trapped in the fluid shaped like clouds bubbles (Evans, .1990).The depth of bubbles penetration from the falling liquid jet influences the rate of gasentrainment. The maximum penetration depth of bubbles has a correlation to theeffects of nozzle geometry (Ito, et al., 2000).

The push force phenomenon of vertically falling water to the surface of the

water will carry a small air bubbles into the reactor medium. The collision of fluidflow can be enough to bring the next bubble completely to the bottom of vessel. Theflow of water that falls towards a level of liquid surface will attract all thesurrounding airflow. It will stimulate the surface of the liquid to form a trumpet. Ifthe flow velocity is high enough, the air bubbles will be drawn down, which follows


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the movement of the liquid and then the liquid will rise to the surface. This happensfor two reasons (Setiadi, et al., 2007; 2009):

1. Air that is trapped between the falling flow limit and trumpet -shaped surface profile is carried below the surface.

2. Surface turbulence of the falling flow is mixed with the air in the eddy currentand carried beneath the surface.

The amount of gas / air-borne at each stream can be seen if they are allowedto fall on the surface of the calm water. Slow liquid flow will not form bubbles

populations significantly, but a faster flow (liquid jet) will form bubbles that cancause a bubble cloud. On the phenomenon of mass transfer processes, which would

be the occurrence of mass transfer into the liquid phase. The fluid flow velocitydepends on the design and size of the nozzle diameter.

2. RESEARCH METHOD Experiment Method

The materials used in the column is water. Equipment circuit schematicshown in Figure 1. Jet bubble column consists of a column (outer tube) and thedowncomer pipe (the tube) made of acrylic cylinder which has a diameter of 100mmand each 36mm with 2mm thickness, and height 80cm. Initially, pour water into thecolumn with a volume of 10L, flowed by using pumps. Liquid volumetric flow rate is

set in Valve 1. The intake process (gas entrainment) occurs because of the fluid thatcomes out of the nozzle in speed jet mashing the stagnant liquid in the column.Volumetric rate of air that is inhaled into the column (Q g) measured with a flowmeter. The process of contact between the wastewater and the air will lead to theemergence of small air bubbles that will affect the height difference of the wastewatercontained in the column (H f ) and additional capillary column (h f ). Data the length of

bubble penetration depth (Z) is obtained from measuring devices contained in thecolumn.

Variable of process conditions for this study, conducted in variation ofdiameter nozzle (D n) at 8, 10, 12, and 12.7 mm, nozzle height (H n) at 12.5; 15; 20,

and 25 cm, and the liquid volumetric flow rate (Q 1).

Figure 1 Schematic circuit equipment jet bubble column.


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Calculation of the correlation on the maximum penetration depth of airbubbles.

In relation to the rate of air that is inhaled into column toward the fall of jet liquid,the effect of the nozzle contraction angle and nozzle length is the equation correlationthat were previously carried out by the researchers (Ito, et al., 2000);

Calculation of gas phase holdup

The equation used to calculate the gas phase holdup based on the basic principles of pressure on a vessel (Setiadi, et al., 2007):

3. RESULTS AND DISCUSSION Correlation on the penetration depth of bubbles

The maximum penetration depth of air bubbles are the result of the energymomentum derived from the velocity of liquid jet that occurs in the column. From theresults of research-conducted, the maximum penetration depth profiles of air bubblesobtained volumetric rate on different liquids at different nozzle diameter (Figure 2).The maximum penetration depth profile of air bubbles toward the volumetric rate ondifferent liquids at the nozzle height toward the surface of the liquid (H n) is different

(Figure 3). The data of maximum penetration depth bubble obtained from the meter-measuring tool (unit of length) contained in the column. The maximum penetrationdepth profile of the bubble shows a linear relationship to the velocity of liquid jet.Figure 2 shows the average value of the coefficient determination (R 2) is 0.970 to0.986 (almost 1) for the different size of the nozzle diameter (D n) and the height ofnozzle to the surface of the liquid (H n) is 15 cm. For all of these profiles, themaximum penetration depth of bubbles (Z) is greater for the higher liquid volumetricrate. This is inversely proportion to the diameter of the nozzle where the maximum

penetration depth of the bubble will be greater if the nozzle diameter is smaller. Thishappens because the speed of the jet coming out of the nozzle (V n) and the liquidcollision energy is greater.

Figure 2. Effect of nozzle diameter on the penetration depth of bubbles in variousliquid volumetric rate (Q 1) and constant nozzle height (H n = 15 cm).


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Figure 3 shows the maximum penetration depth of the bubble getting bigger as well

as closer distance between the nozzles with the liquid surface. The calculation is todetermine the empirical constants simultaneously from equation (1) and the results onseveral other nozzle diameter shown in Table 1. In Figure 4, the relationship betweenthe dimension of maximum penetration of air bubbles on the experimental results andthe model, have a relative error rate 10%, this means correlation of maximum

penetration depth of air bubbles model is nearly similar to the experimental.

Table 1: Calculation of the empirical constants related to bubble penetration (at =90o)

Figure 3. Effect of nozzle height on the bubble penetration depth at various liquidvolumetric rate (Q 1) and at nozzle diameter (D n = 8 mm).

Figure 4. The correlation dimension of maximum penetration depth of bubbles on ( = 90 o). Gas phase holdup and gas entrainment

Gas phase holdup was calculated from the static pressure data in the form of aerationliquid height in column (H f ) and height of liquid in the extra capillary tube (h f ).

Where the liquid height obtained from data in the additional capillary column (Figure5 and Figure 6). From the experimental data obtained from the calculations, it can bemade the gas phase holdup profiles for liquid jet velocity at different nozzle diameterand the height of the nozzle toward the liquid (H n) 12.5 cm.

Figure 5 Effect of nozzle diameter on gas holdup; at various high volumetric rate ofliquid and constant nozzle (H n = 12,5cm)

Figure 5 shown, the holdup profile of gas phase is greater for the higher liquid jetvelocity at the constant size of the nozzle. Furthermore, the smaller diameter nozzlewill produce greater gas phase holdup. This is due to the energy that strikes the liquidin greater downcomer column, resulting static pressure at the greater liquid depth(increasingly collision). Furthermore, the smaller nozzle diameter will affect to thesize of the liquid jet. As the smaller liquid jet will produce a greater depth ofcollisions and increase the flow vortex intensively.


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Figure 6. Effect of nozzle height on the gas holdup; at various liquid volumetric rateand nozzle diameter (D n = 8mm)

Figure 6 shown, nozzle height does not have a very significant effect on the gasholdup at a greater liquid volumetric rate and constant nozzle diameter. This is due tothe ratio between the volumetric flows rates of gas to volumetric flow rate of liquidhave a similarity to the liquid velocity that comes out of the nozzle.

Entrainment gas is inhaled gases due to energy momentum derived from liquid jetvelocity. The data of inhaled gas rate obtained from measuring tool, flow meter. FromFigure 6, inhaled gas volumetric rate is greater for higher liquid volumetric rate on aconstant nozzle height. Likewise, the smaller diameter nozzle will result a greatervolumetric rate of gas entrainment. This is due to the existence of the greaterincoming energy momentum and the addition of the liquid volumetric flow rate andthe size of the nozzle diameter. It results a greater depth of penetration in thedowncomer column. Moreover, it can increase intensively the vortex flow that cancause larger inhaled gas into downcomer column (Setiadi, et al., 2007).

Figure 7. Effect of nozzle diameter on gas volumetric rates at different liquidvolumetric rates and constant nozzle height (Hn = 12,5cm).

Figure 8 shown, nozzle height does not have a very significant effect on the rate ofvolumetric gas entrainment at a greater liquid volumetric rates. This is due to the ratioof gas volumetric flow rate to liquid volumetric flow rate have similarity at any fluidvelocity that comes out of the nozzle.

Figure 8. Effect of nozzle height on the gas volumetric rate at various liquidvolumetric rate and constant nozzle diameter (D n=8 mm).

4. CONCLUSION

The maximum penetration depth of gas bubbles / air (Z), gas holdup ( g), and gasentrainment (Q g) the greater in line with the increasing size of the nozzle diameter(Dn).

The maximum depth of penetration of gas bubbles / air (Z), gas holdup ( g), and


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gas entrainment (Q g) the greater in line with the increasing size of liquidvolumetric rate (Q l).

Nozzle height does not have a very significant effect on the gas holdup or gasentrainment rate.

5. ACKNOWLEDGEMENTS

We would like to express our gratitude to the Directorate of Research andCommunity Service DIKTI who has given us a mandate for Research Grant 2014.

NOTATION

A,B,C,D,E Empirical Constants, (-)Dn Nozzle Diameter, (dm)

Fr Jet Froude number , (-)g Gravity Force (dm/menit 2)hf Liquid Height at additional capillary tube, (cm)H f Liquid height at column, (cm)Hn Nozzle Height , (dm)Ln Nozzle Length , (dm)Qg Air Volumetric Rate, (L/minute)Q l Liquid Volumetric Rate, (L/minute)v Liquid Velocity (L/minute)Vn Liquid jet velocity from Nozzle (m/s)

g Gas Phase holdup, (-) Z Maximum Penetration Depth of bubbles (dm)

Nozzle contraction angle (degree)

hasil translate-pengaruh nozzle terhadap kinerja kolom gelembung pancaran (t)

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