Bab 2 bing

BAB II

TINJAUAN PUSTAKA

II.1 Teori dasar

II.1.1 Fluid

The flow and behavior of a fluids is important in many

operations in process engineering. A fluid may be defined as

a substance that does not permanently resist distortion and,

hance, will change its shape. In this text gases, liquids,

and vapors are considered to have the characteristics of

fluids and to obey many of the same laws (Geankoplis, 1997).

In the process industries, many of the materials are in

fluid from and must be stored, handled, pumped, and

processed, so it is necessary that we become familiar with

the principles that govern the flow of fluids and also with

the equipment used. Typical fluids encountered includewater,

air, CO2, oil,slurries, and thick syrups (Geankoplis, 1997).

If a fluid is inappreciably affected by changes in pressure,

it is said to be incompressible. Most liquids are incompressible.

Gases are considered to be compressible fluids. However, if gases

are subjected to small and they can be considered to be

incompressible (Geankoplis, 1997).

Like alll physical matter, a fluid is composed of an

extremely large number of molecules per unit volume. A theory such

as the kinetic theory of gases or statistical mechanics treats the

motions of moleculess in terms of statistical groups and not in

termsof statistical groups and not in terms of individual

molecules (Geankoplis, 1997).

I-1

Laboratorium Operasi TeknikKimia I

Program Studi D3 Teknik

BAB II TINJAUAN PUSTAKA

Fluid Classification

a. Incompressible fluid is a fluid that has a density which is affected slightly by

the rather large changes in temperature and pressure. Contoh : zat

cair

b. Compressible fluid is a fluid that has a density that is sensitive to changes in

temperature and pressure. Example: oxidizing gas

c. Static Fluid (Fluid silent)

Study the fluid at rest and the fluid that is in a place, and there is no

movement between the surrounding elements.

d. Fluid Dynamic (Fluid moves)

No fluid movement between the surrounding elements.

e. Newtonian fluid (a term derived from the name of Isaac Newton)Adalah

suatu fluida yang memiliki

kurva tegangan/regangan yang linier. Contoh umum dari

fluida yang memiliki karakteristik ini adalah air.

b.Fluida non-Newtonian

Adalah suatu fluida yang akan mengalami perubahan

viskositas ketika terdapat gaya yang bekerja pada fluida

tersebut. Hal ini menyebabkan fluida non-Newtonian tidak

memiliki viskositas yang konstan. Berkebalikan dengan

fluida non-Newtonian, pada fluida Newtonian viskositas

bernilai konstan sekalipun terdapat gaya yang bekerja

pada fluida (wikipedia, 2013).

II.1.2 Bernoulli Principal

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http://id.wikipedia.org/wiki/Fluida

http://id.wikipedia.org/wiki/Fluida_Newtonian

http://id.wikipedia.org/wiki/Viskositas

http://id.wikipedia.org/wiki/Fluida

http://id.wikipedia.org/wiki/Air

http://id.wikipedia.org/w/index.php?title=Linier&action=edit&redlink=1

http://id.wikipedia.org/w/index.php?title=Regangan&action=edit&redlink=1

http://id.wikipedia.org/w/index.php?title=Tegangan&action=edit&redlink=1

Laboratorium Operasi Teknik Kimia IProgram Studi D3 Teknik


If there is no energy added to the system as work or

heat, then the total energy of the fluid is converted. In a

special case where no mechanical energy is added and no

friction then become Bernoulli equation, for turbulent flow

which is of sufficient importance to deserve further

discussion.

Gambar II.1.1 Keseimbangan massa pada sistem aliran

this equation covers many important practical situation

and is often used conjuction with the mass balance equation

for steady state.

(Geankoplis, 1997)

II.1.3 Pump

In order to make fluid flow from one point to another in

a closed system or pipe, it is necessary to have driving

force. Sometimes this force is supplied by gravity, where

different in elevation occur. Sometimes energy or driving

force is supplied by mechanical device like pump or blower,

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which increases the mechanic energy of fluid. This energy may

used to increase the velocity, pressure or difference

elevation of the fluids, which seen in mechanical energy

balance equation, which relates v,p,ρ and work. the most

common methods of adding energy are by positive displacement

or centrifugal action.

Generally, the word “pump” is defined as a machine or

device for moving on incompressible liquid. Fans, blower, and

compressor are devices to transfer gas, usually air (Geankoplis,

1997).

II.1.4 Pump Classification

based on the work principle, pumps are classified into :

1. Positive Displacement pump

this pump produce intermitten capacity because the fluid

is pressed in the pump elements with certain volume. Next

positive displacement pumps are classified based on how it’s

move :

Reciprocating pump

Piston pump

Diaphragm Pump

Rotary Pump

Single Rotor pump

Multiple Rotor pump

2. Dynamic Pump

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Dynamic pump is a pump without change of the position

while its working. this pump has a rotor as a prior element

with an impeller spinning in a high speed. when fluid

transferred into the pump, it is accelerated by impeller

which increase fluid absolute velocity, pressure and throw it

trough volut.

Classification of dynamic pump:

Centrifugal Pump :

Axial Pump

Mixed Flow dan Radial Flow pump

Peripheral Pump

Special effect pump :

Jet pump

Gas Lift pump

Hydraulic RAM pump

Electromagnetic Pump(Igor J. Karassik, 2008)

II.1.5 Centrifugal Pump

This type of pump can only be used for gas and liquid

that does not contain impurities. Centrifugal pump sometimes

is made to suck its own by making a small vacuum pump

according to the principle of liquid bracelet inside or

attached to the pump. So that all air can be sucked out, then

the suction part of the small vacuum pump should be connected

at the highest point of the suction channel.

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II.1.5.1 Work of Centrifugal Pump

The liquid is forced into an impeller by atmospheric

pressure, or in the case of jet pump by artificial pressure.

Impeller fan forward kinetic energy to the liquid, causing

the liquid to spin. The liquid leaves the impeller at high

speed. The impeller is surrounded by a volute casing or in

the case of a turbine pump stationary diffuser. Stationary

volute or diffuser ring converts the kinetic energy into

pressure energy.

II.1.5.2 Parts of Centrifugal Pump

Gambar II.1.2 Parts of Centrifugal Pump

Bagian pompa yang tidak bergerak :

1. Base Plate

Serves to support all parts of the pump and the pump

position on the foundation.

2. Casing

Casing is the outermost part of the pump house that serves

as:

• Protector of all rotating elements

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• The position of the guide vane diffuser, inlet and outlet

nozzle

• Place which give the direction of flow of the impeller

• Place convert kinetic energy into energy press.

3. Container

The main function of the container is closed the impeller

at suction and delivery ends and so shaped tank pressure.

4. Difuser guide vane

This section usually form part of the casing or assembled on

the casing by means of bolted. This section serves to:

• Directing the flow of fluid to the volute or to the next

stage.

• Changing the fluid kinetic energy into pressure energy

5. Stuffing box

The main function of stuffing box is to prevent the

leakage in the area where the pump penetratethe casing

6. Wearing ring ( Cincin penahan arus )

Wearing Ring is assembled on the casing (not spinning)

as wearing rings casing and assembled on the impeller

(rotating) as the impeller wearing ring. The main function

of wearing rings is to minimize the leakage of fluid from

the impeller that goes back into the eye of the impeller.

7. Discharge nozzle

Discharge nozzle is the channel fluid out of the pump and

also to increase the pressure out of the pump energy. (awan,

2009)

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II.1.5.3 Pump moving part :

1. Shaft

Shaft serves to continue the drive torque of the pump

during operation, and is the seat of the impeller and other

rotating parts.

2. Shaft sleeve

Shaft sleeve serves to protect the shaft from

erosion, corrosion and wear, especially if it past the

stuffing box shaft.

3. Wearing ring

Wearing Ring is assembled on the casing (not

spinning) as wearing rings casing and assembled on the

impeller (rotating) as the impeller wearing ring. The main

function of wearing rings is to minimize the leakage of

fluid from the impeller that goes back into the eye of the

impeller.

4. Impeller

Impeller serves to transform the mechanical energy of

the pump energy into the fluid velocity in the pumped

continuously, so the liquid on the suction side

continuously will also fill the void due to the

displacement of fluids before. (awan, 2009)

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Gambar II.1.3 Centrifugal Pump(Geankoplis, 1997)

Many factors to establish the actual efficiency and

performance characteristics of the pump. Therefore, it is

necessary to establish performance characteristics of the

pump experimentally. Performance is usually expressed by

using a pump manufacturing curve called a pump characteristic

curve. Head H (m) is generated will be the same for any

liquid of the same viscosity. The resulting pressure, P1 =

H.ρ.g, will be proportional to the density. Less than 0.05

Pa.s viscosity (50 cp) has little effect on the resulting

head (Geankoplis, 1997).

II.1.5.4 Advantage and Disadvantage of Centrifugal Pump

The advantages of centrifugal pumps include:

1. Cheaper price

2. Construction is simple pump

3. Easy installation and maintenance

4. Capacity and high tap (head) high

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5. High reliability and durability

Disadvantages of centrifugal pumps include:

1. Limited pengembus pressure (delivery pressure)

2. Not being able to lure the fluid itself. So it is usually

used multingkat same wheelbase and is driven by a motor(Repository.USU.ac.id, 2007)

Pheriperal Pump

Peripheral pumps or regenerative pump is a centrifugal

pump with moving wheels so it is called as a form of

peripherals. Almost all of the characteristics of different

peripherals wheel very far with radial wheels. At the highest

and lowest pressure needed the highest rate of high energy.

Work of Pheriperal Pump

fluid get in the pump and go out during some periods.

Increasing of fluid velocity gradually increases when

compared with centrifugal pumps.

Gambar II.1.4 Pheriperal Pump

advantage of pheriperal pump:

• Economical because less energy is used than centrifugal

pumps.

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• Easy to use because it has a simpler design than

centrifugal pumps.

• Suitable for use in households and industry.

Disadvantages pheriperal pump:

• Maintenance costs are not cheap.

Gambar II.1.5 Curve of Centrifugal Pump and Pheriperal Pump

Cavitation

Steam bubbles on the liquid side of a pump caused by

rapid local pressure drop that occurs very close to or

touching the pump casing or impeller. So the pressure

reduction causes the bubbles collapse and rupture, and cause

cavitation. Cavitation produces noise and vibration and cause

the pump loses the hydrodinamik efficiency. It is influence

the boiling point, which occurs when the heat arising at the(Wahren, 1997).

The Caused of Cavitation on Centrifugal Pump

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The centrifugal pump has technical properties that must

be met in order to operate properly. One of the problems that

often occur in this type of pump is a pump failure in the

process of priming, so pump can not suck and pumping

eventually fail and cause damage to parts of the pump.

There are several causes of cavitation in centrifugal pumps

them, are:

1. Vaporation (evaporation)

2. Water ingestion (entry of outside air into the system)

3. Internal recirculation (recirculation within the system)

4. Turbulance (turbulence flow)

5. Vane Passing Syndrome

How to avoid cavitation process is most appropriate to the

installation of the pump NPSH available is greater than the

NPSH required (scribd, 2006).

II.1.6 Charateristic of Pump System

II.1.6.1 System Resistance (head)

a. Static Head

Static head is the height difference between the source

and destination of the fluid being pumped (see Figure

II.1.2a). Static head is independent flow (see Figure

II.1.2b). Static head at certain pressure depends on the

weight of the liquid and can be calculated by the following

equation:

Static head is composed of:

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• Static suction head (hS): resulting from the removal of

the fluid relative to the center line of the pump. hS is

positive if the liquid level is above pump centerline, and

negative if the level is below the center line of the pump

(also called "suction lifter")

• Static discharge head (hd): vertical distance between the

center line of the pump and liquid level in the tank

purposes.

Gambar II.1.6 Head Statik

b. Head friction (hf)

This is a loss that is necessary to overcome the

resistance to flow in pipes and fittings. Head is depend on

the size, condition and type of pipe, number and type of

fittings, flow, and the nature of the fluid. Head friction /

friction is proportional to the square of the flow rate as

shown in Figure II.1.6. Closed-loop circulation system

showing only head friction / friction (not the static head).

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Head Equation

Head is the vertical distance between the center line of the

pump and liquid level in the tank purposes

Head =

(Geankoplis, 1997)

Head loss :

Fanning did a lot of experiments to provide friction factor

data, but the head loss calculation has been implemented by

using the equation of hydraulic radius (not diameter pipe).

• The calculation involves dividing the hydraulic radius of

the cross sectional area of the flow area by the wetted

perimeter.

• For pipes with a full stream flow, the hydraulic radius is

equal to ¼ the diameter of the pipe, so that the head loss

equation becomes:

hf = f f(L/Rh) x (v2/2g)

Dimana Rh adalah hydraulic radius (¼ diameter pipa) dan

f f adalah fanning friction factor (Geankoplis, 2003).

c. Friction Factor

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This alternative method is used to calculate the friction

factor which does not require the completion of iteration.

In search of a friction or head loss in a straight pipe, the

friction factor is needed. One example of friction factors,

namely:

Friction Factor Equation Chen (on condition darcy friction

factor)

(Anonim, 2012)

if on the condition of the friction factor Fanning friction

factor equation Chen:

Dimana :

f = Friction Factor Chen equation

ɛ = Roughness of pipe (ft)

D = Diameter dalam Pipa (ft) (Campbell, 2007)

d. Friction on Straight Pipe

Loss of friction due to the friction experienced by the

fluid movement in the pipes which usually can be calculated

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through the Darcy-Weisbach equation relationship as

follows:

Dimana :

F = Friksi pada pipa lurus (m)

f = Faktor friksi Darcy

L = Panjang Pipa Lurus (m)

D = Diameter Pipa dalam (m)

V = Kecepatan Linier Fluida (ft/s)

g = Percepatan Gravitasi (m/s2)(Campbell, 2007)

e. friction on fitting

Valve and Fitting have an influence on the friction

loss of a flow system

perpompaan with each owned friction coefficient, can

usually be counted through the equation:

Dimana :

Hf = Head loss atau friksi pada fitting (m)

Kf = Koefisien friksi

v = Kecepatan linier (m/s)

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V2

g = Percepatan gravitasi (m/s2)

= Velocity head (ft)

(Anonim, 2012)

f. Difference of big pipe to small pipe

(sudden contraction losses)

Gambar II.1.7 Sudden Contraction

hc = 0,55

(Geankoplis, 1997)

g. Difference of small pipe to big pipe

(sudden enlargement losses)

Gambar II.1.8 Sudden Enlargement

hex =

(Geankoplis, 1997)

h. Velocity head

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V1

A1

A2

A2

V2A1

V2




This term refers to the kinetic energy of a moving

fluid at the specified point in the pump system. ie move the

fluid at the specified point in the pumping system.

Where V is the velocity of fluid flow in the pipe (m / s)

and g (m/s2) is the acceleration due to gravity (Wahren, 1997)

II.1.6.2 Flow Fluid Velocity

There are 2 kinds of fluid flow velocity:

a. linear velocity

Is the distance traveled by the fluid flowing per unit

time and is not influenced by certain factors sectional

area. Unit v (m / sec) and (cm / sec)

(Geankoplis, 1997)

b. Volumetric velocity (discharge)

Is a measure of the amount of water flowing volume

that can be accommodated for a certain time and is

influenced by geometric factors, cross-sectional area of

the fluid flowing places.

Debit represented by the following equation:

dimana:

Q : debit satuannya m3/sec (MKS) dan cm3/sec (cgs)II-18



V : volume satuannya m3 (MKS) atau cm3 (cgs)

∆t: selang waktu tertentu satuannya (s)

II.1.6.3 Horse Power

a. WHP (Water Horse Power)

Water Horse Power (WHP) adalah liquid horse power yang

disampaikan oleh pompa.

(Wahren, 1997)

b. BHP (Brake Horse Power)

When choosing a pump is first necessary to determine the flow

capacity and the required pump head. Although many pumps

which can meet the operating conditions. Required operating

conditions are about the size of the motor and the pump

efficiency is needed. Now the power is transmitted from the

motor to the pump is also a product of the torque on the

drive shaft and the pump shaft angular velocity:

BHP= Γ. ω

Dimana :

BHP = Break Horse Power (kW)

Γ = Torsi (Nm)

Γ =

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Dimana :

= Densitas fluida (kg/m3)

Q = Debit (m3/s)

= Kecepatan sudut (putaran/s)

Ri = Jari-jari impeler (m)(Darby, 2001)

II.1.6.4 Efficiency

Efficiency is expressed as a percentage that represents a

unit of measurement that describes the change of centrifugal

force and is expressed as a change of pace into pressure

energy.

η =

II.1.6.5 Barometer (Bourdon Pressure Gauge)

Bourdon tube pressure gauge is a pressure measurement

instrument non-liquid. Bourdon tube with oval tubular

reservoir and consists of short curved hollow pipe and one

end closed.

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Gambar II.1.9 Bourdon Pressure Gauge

The principle works:

The resulting changes in proportion to the applied

pressure. Pressure changes detected by the Bourdon tube will

cause the tube to move. Then the tube movement is transmitted

to drive the meter needle. The pressure scale is usually

calibrated in several sizes include: psi, kPa, bar and

kg/cm2.

usage:

Used to measure the pressure of the fluid in the pipe. The

pressure in the pipe causing the pipe to the appliance will

change shape.

Bourdon there are 3 types:

1. C-type Bourdon Tube

• Used in the range 15-100000 psig.

• Range accuracy is ± 0,1 - 5% span (span is the sensor

measurement range).

2. Spiral Bourdon Tube

• Used at medium pressure range.

• Available in a range of up to 100,000 psig.

• Range accuracy is ± 0.5% of span.

3. Helical Bourdon Tube

• Used in the range of 100-80000 psig.

• Range accuracy is ± ½ - 1% of span.

Advantage :

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• Characteristically portable (can be taken anywhere).

• Accuracy high enough

• Not easily affected by changes in temperature.

• Both are used to measure the pressure between 30-100000

Psi.

Disadvantages:

• Measurement is limited to static pressure.

• Influenced by shock and vibration.

• At low pressure 0-30 psi less sensitive. (Scribd, 2011)

II.1.6.6 Pump Charateristic Curve

Pump characteristic curve is influenced by the size and

design of large pumps, the size of the diameter of the

impeller, and a large round operasionalnya.Karakteristik

demonstrated through a pump head curve with the pump

discharge (Anonim, 2013)

Gambar II.1.10 Kurva Karakteristik Pompa Centrifugal

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II.1.7 Various Type of Valve and Fitting

Valve or valve is also called a tool to regulate the flow

of a fluid by closing , opening or inhibit a portion of the

flow path . Liability for a pipeline engineer to know at

least the basics of this valve . valve on the vessel plays an

important role in the plumbing installation , plumbing

installation either ship fuel , ballast , bilge , sanitary ,

and other .

The types of valve that is often used is the gate valve ,

globe valve , Butterfly valve , ball valve , Plug Valve ,

Check Valve and Non - Return Valve or .

1 . Gate Valve ( Valve )

This type of valve has a sealing disc shape, or often

called the wedge , which is driven upwards down to open and

close. Usually used for open or closed position is perfect

and is not recommended for most open positions. Valve ( Valve

) is called a gate valve because it contains an element

called the gate closure that stops flowing . The door acts

like a shutter gate that separates the inside of the house

from the outside or the door separating the two rooms.

A vertical disc housed in a slide gate valve body up and

down at right angles to the direction of flow in the pipe,

close or open the valve. Flow is blocked by using wedge -

lock effect disc valve / valve it.

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2. Globe Valve

Valve type globe valve / valves typically used to adjust

the amount of fluid flow. Globe valve named after its shape.

form of a globe valve has interior partitions, and valve

inlet and outlet centers are inline. This configuration force

changes the direction of flow in the form of S.

Disk inhibit fluid flow by pressing against the seat in

the partition. Concept: againts force by changing the

position of the disc globe valve, globe valves can be used

for both throttling and for full-on, full-off flow control.

Gambar II.1.12 Globe valve

3. Butterfly Valve

The shape is a disc that has the insulation must pivot in

the middle. According to the design of this type of valve,

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Gambar II.1.11 Gate valve saat tertutup



can be divided into concentric and eccentric. Eccentric has a

design that is more difficult but has better functionality

than concentric. The form is simple to make lighter than

other valve.

Gambar II.1.13 Komponen Butterfly Valve

4. Elbow

The flow of a fluid in the elbow while becoming more

turbulent, because it would rapid corrosion and erosion

occurred

Gambar II.1.14 Elbow

5. Reducer

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This type has a tilt angle formed more horizontal flow,

therefore this type horizontally to drain the fluid and

relieve the flow free of a gas (McCabe, 1993).

Gambar II.1.15 Reducer

6. Coupling

There are many kinds of coupling connection, most of

the fluid kekedapan by tightening an elastic rubber

packing.

Gambar II.1.16 Coupling

7. Union

Union usually use for small pipe

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Gambar II.1.17 Union

5. Tee

This type has a flow line and branch. At the branch

flow is often encountered when exiting or shrinking the

size equal to the size of the entrance. This species is

common and not hard to transform and sought, in addition

to easy this kind of economical and not easily eroded(McCabe, 1993)

Gambar II.1.18 Tee

II.2Aplikasi Industri

Studi Awal Kajian Bubble Pada Pompa Sentripugal Yang

Diukur

Dengan Sinyal VibrasiOleh: Iswan Ansukarto Sukardi

11 Juni 2012

II.2.1 Pendahuluan

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Pompa centrifugal adalah jenis pompa yang sangat banyak

dipakai oleh industri terutama pengolahan dan pendistribusian

air bekerja dengan prinsip putaran impeler sebagai elemen

pemindah fluida yang digerakkan oleh suatu penggerak mula.

Zat cair akan berputar akibat dorongan sudu-sudu dan

menimbulkan gaya centrifugal yang menyebabkan cairan mengalir

dari tengah impeler dan keluar melalui saluran sudu-sudu dan

meninggalkan impeler dengan kecepatan tinggi. Cairan dengan

kecepatan tinggi ini dilewatkan saluran yang penampangnya

makin membesar sehingga terjadi perubahan head (tinggi tekan)

kecepatan menjadi head tekanan. Setelah cairan dilemparkan

oleh impeller, ruang diantara sudu-sudu menjadi vacuum,

menyebabkan cairan akan terhisap masuk sehingga terjadi

proses pengisapan. Memperhatikan hal tersebut dan dengan

luasnya aplikasi penggunaan pompa centripugal ini, maka

diperlukan stabilitas yang tinggi dan performansi yang sangat

prima dan dapat diandalkan,dan apabila turunnya performansi

pompa secara tiba-tiba dalam operasi sering menjadi masalah

dan mengganggu kinerja sistem secara keseluruhan. Turunnya

performansi pompa secara tiba-tiba dan ketidakstabilan dalam

operasi akan menjadi masalah, indikasi penyebab turunnya

performansi pompa adalah salah satunya disebabkan oleh

kavitasi (cavitation). Kavitasi didefinisikan sebagai

pembentukan rongga kosong dalam suatu cairan dengan high forces

dan kemudian pecah, kavitasi ini terjadi ketika cairan

tersebut berada pada daerah yang mengalami perubahan tekanan

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dengan cepat. Fenomema ini sangat berbahaya dan diketahui

sebagai fenomena yang bersifat merusak pada bagian-bagian

penting instrument pompa dan menurunkan performansi dari

pompa itu sendiri. Dalam hal kavitasi ini bagian pompa yang

sering mengalami kavitasi adalah sisi isap pompa. Hal ini

terjadi jika tekanan isap pompa terlalu rendah hingga dibawah

tekanan uap jenuh.

II.2.2 Metodologi Percobaan

Tujuan umum dari penelitian ini adalah pemantauan bubbles

yang akan timbul pada

daerah impeler yan mengakibatkan timbulnya getaran yan

spesifik, pengukuran getaran tersebu dilakukan dengan

menggunakan sinyal vibrasi getaran dengan memvariasika valve

untuk mendapatkan varias kapasitas yang masuk pada pipa isap.

Data yang diperoleh berupa data dinamis selanjutnya

ditransfer ke komputer untuk diolah dan ditampilkan dalam

bentuk table dan grafik. Hasil pengolahan data tersebut yang

berupa laporan akan dianalisa untuk mengetahui pengaruh

bubble yang terjadi terhadap karakteristik getaran yang

terjadi. Adapun variable yang diamati adalah : 1) Frekuensi

dan accelerasi pada jerk 2) Kapasitas pompa 3) Putaran pompa 4)

Tekanan pada sisi isap dan tekan 5) Bubble yang terjadi setiap

bukaan 6) Tegangan input maksimum 7) Tegangan input minimum.

II.2.3 Pembahasan

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Pelaksanaan penelitian ini dilakukan pada sebuah

instalasi pompa yang telah dilengkapi dengan instalasi pipa

dan instalasi listrik, bak penampung air, yang telah

dilengkapi dengan alat ukur baik alat ukur aliran air ataupun

tekanan air dalam pipa. Pompa sebagai objek penelitian

dipasang dengan nilai NPSHR pompa adalah 10,20 m yang

diperoleh dari pabrik pembuat pompa, sedangkan instalasi

pompa tersebut dilakukan perubahan pada pipa isap yaitu

menambah panjang pipa isap dengan total panjang pipa isap

sebesar 2,7 m. Pengambilan data yang dilakukan untuk

mendapatkan karakteristik bubble adalah dengan melakukan

mengontrol bukaan valve pada pipa isap dengan bukaan 100 %,

75%,50% dan 25% dan prilaku getaran berupa displasment,

velocity dan accelerasi berdasarkan time domain. Untuk

pengamatan bubble digunakan camera high speed agar dapat

diketahui karakteristik bubble dengan mengukur karakteristik

getaran yang terjadi. Berdasarkan hasil pengamatan pada pompa

centrifugal tersebut bahwa terjadinya berubahan putaran pada

poros pompa dan perubahan vibrasi yang kemudian diikuti

terjadi bubble yang dimulai pada sisi pipa isap. Hubungan

Karakteristik getaran dengan fenomena kavitasi didapat dengan

melakukan pengambilan data. Dalam pengamatan yang dilakukan

secara secara visual pada pipa isap saat masuk ke sisi masuk

impeller telah terjadi pertumbuhan bubble pada bukaan 50%

dengan nilai akselerasi 0,305 m/s2, telah terjadi kavitasi

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karena bubble telah pecah, secara visual bubble tidak

terlihat pada impeller.

II.2.4 Kesimpulan

Berdasarkan tujuan penelitian yaitu pemantauan bubbles

yang timbul pada daerah impeler yang mengakibatkan timbulnya

getaran yang spesifik, maka berdasarkan hasil penelitian dan

pembahasan maka dapat disimpulkan bahwa: 1.) Fenomena

Kavitasi telah terjadi pada bukaan 50% dengan kapasitas

aliran 2,29E-03 sudah terindikasi karena telah terjadi bubble

pada pipa isap dengan akselerasi 0,305 m/s2, dengan amplitudo

-8.50E-06 pada arah horizontal dan bilangan Reynolds 285.844.

2.) Peristiwa pecahnya bubble hanya bisa terlihat di

impeller pada bukaan 25 % dengan kapasitas aliran 2,0E-03

m3/sec pada akselerasi 0,322 m/s2 dengan amplitudo -9,60E-06.

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Bab 2 bing

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