No. Title Allocated Marks (%) Marks

1 Abstract/Summary 52 Introduction 103 Aims 54 Theory 105 Apparatus 56 Methodology/Procedure 107 Results 108 Calculations 109 Discussion 2010 Conclusion 511 Recommendations 512 Reference / Appendix 5

100

UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA ENGINEERING

CHEMICAL ENGINEERING LABORATORY (CHE465)

NAME : MUHAMMAD AMIRUL BIN HASHIMSTUDENT NO. : 2014207844 GROUP : EH 220 2AEXPERIMENT : FREE AND FORCED VORTEXDATE PERFORMED : 14/4/2015SEMESTER : 2PROGRAMME / CODE : EH 220SUBMIT TO : MS NURUL DIYANAH

TOTAL MARKS

Remarks: Checked

by:

---------------------------

Date:

ABSTRACT

Vortex is the rotation of fluid elements around a common center. Its concept was

being used in various types of industry such as turbine design and creating standard

safety against natural disaster. This experiment was carried out to study the

relationship between the surface shape of free and forced vortex. It also to study on the

angular velocity of a rotating liquid in a cylindrical tank. Theoretically, the angular

velocity of the fluid was manipulated by adjusting the control valve to provide different

flow rate of fluid flow. The height of vortex profile was measured when it maintained

constantly at its maximum height. After carried the experiment, it can be conclude that

the height of vortex profile increased as the vortex radius decreased. This conclusion is

obtained from the result of the experiment. For forced vortex , when the angular velocity

of the fluid in the cylinder increases, the depth of each pointer at the different vortex

radius will also increase due to the formation of semi parabolic shape. Therefore, it was

concluded that the height of water surface level is relative to the lowest point of the

surface of a forced vortex flow was directly proportional to the angular velocity of a

rotating liquid in a cylindrical tank and is inversely proportional to the squared radius at

which it was measured.

INTRODUCTION

In fluid dynamics a vortex is a region, in a fluid medium, in which the flow is

mostly rotating on an axis line, the vortical flow that occurs either on a straight-axis or a

curved-axis. Moreover, the plurals of vortex are vortices and vortexes. Examples of

vortices occur in nature, perhaps the most common being a tornado or a whirlpool. A

tornado is formed by high winds whirling around an area of extremely low pressure and

characterised by a funnel shaped cloud. Whirlpools can occur where tides flowing in

different directions meet or at the base of waterfalls where the effect is a spiraling or

swirling of the water again producing a funnel shape.

Basically there are two types of motion translation and rotation. The two may

exist independently or simultaneously. If now an element is represented, it may be

subjected to deformation. This can be linear or angular. If the motion of the particles is

purely translational and the distortion is symmetrical, the flow is irrotational and the

vorticity. Example: Flownet application. Forced vortex is also known as flywheel vortex.

= v C r Free vortex is also known as potential vortex. = v r C. Compound vortex

combination of free and forced vortex also known as Rankine vortex. Spiral vortex (free

vortex and a radial flow). Rotation of a fluid, moving as a solid, about an axis is called

forced vortex motion. Every particle of fluid will have same angular velocity. Free vortex

motion is each particle moves in a circular path with speed varying inversely as the

distance from the centre = vr constant.

This experiment is related to the free and forced vortex flow of fluid in rigid-body

rotation within a cylindrical tank. As mentioned in paragraph 1, vortex is the rotation of

fluid elements around a common center. Mostly the fluid flows in a spinning motion

about an imaginary axis, straight or curved. That motion pattern is called a vortical flow.

There are two types of vortices, which are forced and free. The fluid (or gas) circles

around a center in a forced vortex, while in a free vortex, the medium spirals towards

the center.

In an industry and in a real world, the applications of the vortex flow can be seen

in a various area such as turbine design, natural phenomenon and in creating safety

against natural disaster. Thus, the findings of the experiment are very important to help

the engineers to design a good turbine as the flow of water through the runner of turbine

is a good example that used the principle of forced vortex flow. The findings also can

help engineer in designing a good technology in minimizing the effect of natural disaster

such as tornado and hurricane. Furthermore, the knowledge gain from this experiment

will help students to apply the correct concept in a real situation related to vortex flow as

they already experienced it.

Generally, the apparatus for the study of the shape of "free and forced vortices"

consists of a 250mm diameter cylindrical, transparent vessel 180mm depth, having two

pairs of diametrically opposed inlet tubes of 9.0mm and 12.5mm diameter. The 12.5

diameter inlet tubes which are angles at 15° to the diameter, so that a swirling motion is

imparted to the liquid entering the vessel, are used as entry tubes for the free vortex

experiment. A smooth outlet is centrally positioned in the base of the vessel and a set of

push-in orifices of 24, 16, 12 and 8mm diameter is supplied to reduce the outlet

diameter to a suitable value. The profile of the vortex formed at the top of the vessel is

determined by a gauge, housed on a diametrically mounted bridge piece, which

measures the diameter of the vortex at various depths. This gives the co-ordinate points

required to plot the vortex profile. The forced vortex is created in the vessel described

above by using as the inlet the 90mm bore tubes which are angled at 60° to the

diameter. The input water from these tubes impinges on a simple two blade paddle

which acts as a stirrer / flow straightener. The water "leaves" the vessel via the 12.5mm

diameter angled tubes which are used as "entry tubes for the free vortex experiment.

The two bladed paddle rotates on a vertical shaft supported by a bushed plug, in the

hole used as the outlet for the free vortex experiment, and located at the top by a

suitable hole in the bridge piece fitting across the diameter of the vessel. This bridge

piece also houses the probes required to determine the co-ordinates of the vortex

profile to be measured.

For this experiment, SOLTEQ Free and Forced Vortex (Model: FM42) has been

used. This SOLTEQ Free and Forced Vortex (model FM42) has been designed for

students experiments to produce and measure free and forced vortices. It consists of a

clear acrylic cylinder where the free vortex is generated by water discharging through an

interchangeable orifice in the base of the cylinder. The resulting profile is then

measured using a combined caliper and depth scale. The forced vortex is induced by a

paddle rotated by jets of water at the cylinder base.

The profile of the forced vortex is then determined using a series of depth

gauges. Velocity at any point in the free or forced vortex may be measured using the

appropriate pitot tube supplied. A secondary flow at the base of the free vortex

demonstrated by means of dye crystals (not supplied).

Some of the important cases of forced vortexes are:

The movement of the liquids within the impeller of a centrifugal pump when there is no flow as, for example, when the outlet valves are closed.

The rotation of the liquid within the confines of a stirrer in an agitated tank.

The rotation of liquids in the basket of centrifuge

Figure 1 : shows the example of force vortex formed

THEORY

Free Cylindrical Vortex

When a liquid is flowing out of a tank through a hole at the bottom of the tank, free vortex is formed with the number of oscillation depending on the distortion that created the flow. The liquid is moving spirally towards the center following current, energy per unit mass is assumed to be constant when energy loss by viscosity is neglected. If, while the mass of water is rotating, the central exit hole is plugged, the flow of water in the vertical plane ceases and the motion becomes one of simple rotation in the horizontal plane. This is known as free cylindrical vortex.

Bernoulli’s theorem can be used because the movement is along the flow axis,

ppg

+V2

2g+z=cons tan t

For horizontal plane, the relation becomes

ppg

+V2

2g=cons tan t

Integration of the above relation with r gives

1pg

.dpdr

+Vg

.dVdr

=0 (1)

Next, consider a pair of stream line being divided with distance, δr and is in same horizontal plane and are linked by a fluid tube with wide δA. The centrifugal force of the tube is balanced by the pressure difference between both ends, that is

pg .∂ A .∂ r .V 2

gr=dpdr

.∂ r .∂ A

pgV 2

gr=dpdr (2)

Combine (1) and (2) to produce

V 2

gr+Vg

.dVdr

=0

dVdr

+Vr=0

Integrate above relation to obtain

ln r + ln V = Constant

Vr = K (Constant)

V= Kr

In free cylinder vortex, velocity is inversely proportional to distance from spiral axis, Bernoulli’s theorem is used to determine surface profile as follow:

V 2

2g+z=C (Cons tan t )

(4)

Substitute (3) into (4)

K2

2gr 2+z=C

C−z=K2

2 gr2 (5)

That is, equation for hyperbolic curve yx2

= A that is symmetry to axis of rotation and is horizontal to z = C

Free Vortex

Movement in free vortex is different with free cylindrical vortex because free vortex contains radical velocity towards center. Equation for such situation can be generated by considering the water passes through round segments towards is diameter, where energy passing any tube and is kept constant until

ppg

+V2

2 g+z=cons tan t

If A and V is surface area and velocity of a particular position while A1 and V1 are surface area and velocity at distance r from center circle,

AV = A1V1 = Constant

By taking A = Kr,

V= r 1V 1r

If z is constant,

ppg

+r

12V

12

2 gr2=C

ppg

=C−r

12V

12

2gr 2 (6)

Also,

p1

pg+V

12

2 g=C

p−p1

pg=V

12

2 g−r

12V 12

2gr 2

p−p1

pg=V

12

2g{1−

r11

r12

} (7)

Free vortex can be said as combination of cylinder vortex and radial flow. Velocity is inversely proportional to radius in every case. Angle between flow axis and radius vector at any point is constant and these axis from the spiral pattern.

Forced Vortex

As we know, angular velocity is constant, V= wr

Increase in radial pressure is given by

dpdr

=pV2

r=pω2 r

∫p1

p2

dp= pω2∫r1

r2

rdr

p2−p1 =12pω2(r22−r 12 )

By taking p1=p0 when

r1=0, and

p2=p and r2=r

p−p0

pg=w

2

2 gr 2

Because, p/pg = h, so

h−h0=ω2

2 gr2

h=h0+ω2

2gr 2

This is a parabolic equation.

Surface profile for forced vortex can be represented by equation:

z=Ω2 r2

2 g

Distribution of total head can be represented by equation:

H=Ω2r 2

g

Z = surface profile

ῼ= angular velocity

r = radius

g = gravity

H = total head

Angular velocity can be calculated by:

Ω=2η×revolutiontime(sec)

AIM / OBJECTIVES

Experiment 1: Free Vortex

1. To study on surface profile and speed.

2. To find a relation between surface profile and speed.

Experiment 2: Forced Vortex

1. To study on surface profile and angular velocity.

2. To find a relation between surface profile and total head.

APPARATUS

Orifice of diameter 8mm, 12mm, 16mm, 24mm

Profile measuring gauge

Paddle

Assembly View

1 Bridge 2 Profile measuring gauge

3 9.0 mm diameter, Nozzle 4 Three way inlet valve

5 12.5 mm diameter, Nozzle 6 Inlet

7 Surface profile 8 Outlet valve

9 Outlet 10 Pitot tube

11 orifice 12 Paddle

METHODOLOGY/PROCEDURE

General Start Up:

1. The hydraulic bench tank is filled with water.

2. The study bench is placed on the hydraulic bench.

3. All the accessories must be make sure are ready on the bench such as surface probe, profile measuring gauge, pitot tube, paddle and orifices.

4. The inlet and outlet hose is set up.

5. The stand of the equipment is adjusted to reach the horizontal position.

General Shut Down:

1. The valves are closed and the pump is switched off.

2. The orifices, paddle and other accessories are removed from the cylindrical vessel.

3. The water is drain off from the unit when it is not in used.

Safety Precaution:

1. A proper lab coat must be worn while doing the experiment.

2. The sharpened object is being aware during conducting the experiment.

3. When water is splashed out from tank, that area must be mopped immediately to avoid slippery floor.

Experiment 1: Free Vortex

1. The general start-up procedures are performed.

2. An orifice with diameter 24mm is selected and it is placed on the base of cylinder tank.

3. The output valve is closed and the inlet 3-way valve is adjusted to let the water flows into the tank from two pipes with 12.5 mm diameter. The water is flow out through the orifice.

4. The pump is switched on and the control valve on the hydraulic bench is opened slowly until the tank limit. The water level is maintained by adjusting the control valve.

5. After the water level is stable, the vortex profile is collected by measuring the vortex diameter for several planes using the profile measuring gauge.

6. The profile measuring gauge is pushed down until the both of sharp point touch the water surface.

7. The measured height, h (from the top of the profile measuring gauge to the bridge) is recorded. The value of a (distance from the bridge to the surface of the water level (bottom level of the cutout)) is obtained.

8. The pitot tube is used to measure the velocity by sinking it into the water at the depth of 5 mm from the water surface. The depth of the pitot tube is measured in the water, H.

9. Steps 3 to 8 are repeated for another orifice with diameter 12mm, 16mm and 8mm respectively.

10.The coordinates of vortex profile is plotted for all diameter of orifice in graph and the gradient of the graph is calculated by:

X=K2

2 g.

1r2

11.The graph of velocity which is calculated from the pitot tube reading versus the radius of the profile is plotted.

V=(2gH )0. 5

Theoretically, the velocity can be calculated by using the following equation:

V= Kr

Experiment 2: Force Vortex

1. The general start-up procedures are performed.

2. A closed pump with two pedals is placed on the base of the cylinder tank.

3. The output valve is closed and the inlet 3-way valve is adjusted to let the water flowsinto the tank from two pipes with 9.0 mm diameter. The water can flow out through another two pipes with 12.5 mm diameter.

4. The water is being made sure flow out from the tank with the siphon effect by raising the hose to above the water level in the tank.

5. The outlet hose is being made sure filled with water before letting the water to flow into the sump tank in the hydraulic bench.

6. The angular speed of the pedals is measured by counting the number of circles in a certain times.

7. The surface probe is pushed down until the sharp point touch the water surface.

8. The measured height, (from the top of the measuring gauge to bridge) is recorded.

9. Steps 4 to 8 are repeated with different volumetric flow rate.

10.The coordinates of vortex profile is plotted for different angular velocity.

11.The calculated vortex profile in the same graph is plotted as they related as

h=h0+ω2

2 gr 2

Both experimental and calculated profile is compared

RECOMMENDATIONS

There are few recommendations that can be considered while doing this experiment in

order to get more accurate result:

Repeat the experiment at least twice to get more accurate result, the more data

we get, we can make comparison to determine the best result that can be

pointed out.

Error might happen while taking the time for the number of revolutions since the

paddle that created the forced to the vortex is rotated at the fast rate and this is

difficult for us to get the accurate time. It is best to get the time average.

The velocity of water need to be constant to get the best result so the water flow

need to be adjust and be watched for the whole experiment.

We must make sure that the needles touch the water surface accurately to get

precise data to be used in the further calculations.

It is also important to make sure that the apparatus is in the good condition. It is

because if the apparatus is it not in the good condition its will affect our result.

When we measure the length of the needles, use appropriate ruler such as long

ruler and try to get the average reading which is more accurate.

A better (computerized/digital) mechanism is needed to read the revolution of

paddle associated with time which meant for more precise calculating number of

revolution of paddle in forced vortex at the exact time.

REFERENCES/APPENDIX

1) Cengel, Y.A. & Cimbala J.M. (2006). Fluid Mechanics : Fundamentals and

Applications. Flow in pipes. New York : McGraw Hill, (324).

2) Laboratory Manual of CHE 465 Chemical Engineering Laboratory 1. Fakulti

Kejuruteraan Kimia, Universiti Teknologi Mara.

3) Science direct (n.d). Retrieved 19 May, 2015, from

http://www.sciencedirect.com/science/article/pii/S1026309813000175

4) Chapter 7: Flow of Fluid (n.d). Retrieved 19 May, 2015, from

http://www.nptel.ac.in/courses/112104118/lecture-21/21-2_forced_vortex_flow.htm

5) Free and Forced Vortex (n.d). Retrieved 19 May, 2015, from http://www.jsme-

fed.org/experiment-e/2011_2/003.html

6) Bruce R. Munson, Donald F. Young, John Wiley & son, Inc, FUNDAMENTAL OF

FLUID MECHANICS, 2nd edition.

DISCUSSION

When water flows out of a vessel through a central hole in the base, a free vortex

is formed, the degree of rotation being dependent in initial disturbance. The water

moves spirally towards the center with stream line in motion, so that, neglecting losses

caused by viscosity, the energy per unit mass remains constant. If, while the mass is

rotating, the central hole is plugged, the flow of water in the vertical plane ceases and

the motion becomes one of simple rotation in the horizontal plane, and is known as free

cylindrical vortex.

The free vortex experiment needed us to make an observation upon the vortex

formed while using different size of pitot which will give also different shape of vortex.

Three different in diameter of orifice has been used in this experiment and it was found

that the largest orifice’s diameter, give the larger and fast vortex produced and follows

by orifice’s with medium diameter and the smallest vortex produces using smallest

orifice diameter. This phenomena occurs because the vortex formed is depend on the

size of the orifice used. From the experiment, clearly the larger the orifice used, the

larger the vortex formed. This occurs because when the orifice size gets larger the more

water can flow out from the tank and caused it not accumulated. This vortex was formed

by the force of water flow in the tank and the flow pattern formed is in circumferential.

There are two types of vortices,

Forced vortex Free vortex

In a free vortex, the medium spirals

toward the centre

In a forced vortex, fluid (or gas) circles

around a centre.

If the vortex is to have any longevity, once the material arrives at the centre, it

must exit the system (the red area).  Without a constant supply of energy to remove the

medium from the centre, the Free Vortex ceases to exist.  If the fluid doesn't exit the

system, it no longer has any spiral nature, and becomes a forced vortex.

The experiment was conducted to determine the relationship between the

velocity and angular velocity for free vortex and forced vortex respectively, with the

vortex surface profile. The fluid mass for the free vortex rotates without external force;

only through internal action or some rotation previously imported to it .On the other

hand, forced vortex rotates by a constant torque exerted by some external source onto

the fluid mass.

Here, the water flows out through different orifice diameters of 24mm, 16 mm, 12

mm and 8 mm. Once the flow had stabilized, the diameter at centre, height, pitot tube

head difference and pressure head were recorded and calculated. Here, the water flows

out through different orifice diameters of 24mm, 16 mm, 12 mm and 8 mm. Once the

flow had stabilized, the diameter at centre, height, pitot tube head difference and

pressure head were recorded and calculated.

For experiment of free vortex, an observation of vortex profiles was

performed. In this experiment, three different sizes of orifices were used. For the orifice

size 9 mm, the vortex form was in the smaller radius. For the second orifice which is 15

mm in size, the vortex formed was much larger than the vortex formed by the 9 mm

orifice. The used of orifice in size of 25 mm was the largest vortex formed. This

phenomenon occurs because the vortex formed is dependent on the size of the orifice

used. From the experiment, when the size of orifice gets larger, then the vortex formed

will large too. This occurs because when the orifice size gets larger, the more water can

flow out from the tank. Then it not accumulated. When more water gets out, the larger

vortex formed. This vortex was formed by the force of water flow in the tank. The flow

pattern formed is in circumferential.

For the observation of destruction of the vortex, a core object has been placed at

the center of the orifice. This action will destroy the vortex formed because the flow of

water was block by the core object. When the blocking occurs, the flow rate of the water

through the orifice will decrease. This give more effect on the smaller orifice of 9 mm

cause the flow rate of the water will decrease more than other orifice of 15 mm.

Then the experiment was performed to discover the plotting profiles. The

diameter of the vortex formed was increased proportionally when the size of the orifices

used is much larger. The used of the small orifices will formed the small diameter of

vortex. The larger size of the orifice used the larger the diameter of the vortex formed.

The diameter of the vortex formed is decreased when the depth of the vortex increased.

The measurement of the diameter will result in decreased pattern if the measurement

was taken proportionally to the depth of the vortex formed.

From the results, 24 mm orifice diameter gave the biggest vortex diameter,

followed by the 16 mm, 12 mm and 8 mm. This is because as diameter of orifice

decreases, the vortex diameter also decreases. Also, the theoretical velocities were

calculated from the graph of pressure head against 1/r2 that was plotted.

Forced vortex on the other hand is formed when a liquid is rotated by a paddle

within a tank. The surface profile of forced vortex is a parabolic shape and is dependent

to the angular velocity of the rotation. The rotational speed of the paddle was measured

by counting the number of rotations in 60 seconds. Two trials were conducted where

both used different flow rates of water. The angular velocities were calculated where it

was used to compare the actual and theoretical values centre between by plotting a

graph of height against distance from centre.

In second experiment, the propeller was used to determine the revolution of the

propeller per second (rps). As water flow into the container, it will force the propeller to

move. After increase the velocity, the propeller will spin with more speed. Then, the

velocity of the water need to be maintains and we put the needle to touch the surface of

the water.

As for the forced vortex experiment, we calculate the number of revolution based

on the rotating blades that formed the forced vortex also the length of the needles when

it touched the water surface and compare its value to the calculated length using

specified equation. The average velocity head, hc for the 10, 20, 30, 40, 50 and 60

revolutions in the forced vortex experiment was determined

Based on the graph, all angular speed gives the same result on the trend line

which is when the radius increased, the depth decreased. For all the graphs, some of

the measured depth of the vortex is slightly different from the theoretical values. The

different in height between the measured and the theoretical is due to the error that

occurs during the experiment was conducted.

CONCLUSION

These experiments were carried out in order to determine the surface profile of a

forced vortex and to investigate the physical phenomena associated with a free vortex.

An observation upon vortex that formed and found that small diameter of pitot tube

created small vortex whereas large diameter of orifice created larger vortex. The speed

of circulation of vortex is slow, moderate and fast depends on the size of pitot tube

respectively. In the forced vortex experiment, the result as the average velocity head, hc

for the complete revolution were obtained.

In this experiment, Hydraulic Bench Service Module and Free and Forced Vortex

Apparatus was used in order to achieve the objectives of this experiment. All of the

criteria which are associated to both forced and free vortices have been determined.

From the result of this experiment, the conclusion that can be made here is that the

formation of the vortex is dependent on the size of the orifice used. The disturbance can

destroy the orifice is when some core object blocks the flow of water through the orifice.

The results that attained from this experiment is might deviate compared to the

information found from the theory. The inaccuracy results occurred in this experiment

may caused by some factor like human mistakes, equipment efficiency and other things.

In conclusion, the objective is achieved. As the rotation in the cylinder increases,

the radius of a vortex surface at the axis also will increase. From the results, graph for

the three different speed, the theoretical value for the depth at different vortex radius is

slightly lower than the actual value. Overall, it can be seen that the depth of the vortex

surface, Z is inversely proportional to the radius of vortex, r.

APPENDIX