materi alat penukar kalor_teknik mesin ujb

8/16/2019 Materi Alat Penukar Kalor_Teknik Mesin UJB

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Alat Penukar Kalor

(Heat Exchanger)


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Tujuan Pembelajaran

• Mengenal jenis-jenis alat penukar kalor

• Mengetahui jenis APK yang paling baik untuk

aplikasi industri yang ada • Mengerti parameter kunci dalam desain APK

• Mampu mengestimasi ukuran dan harga APK

• Memiliki latarbelakang untuk menggunakansoftware komersial untuk mendesain APK


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Pendahuluan Heat Exchangers

Untuk apakah Alat Penukar Kalor?

Jenis-Jenis Alat Penukar Kalor

Bagaimana Alat penukar kalor

diklasifikasikan?

Dasar-dasar perencanaan Alat Penukar

Kalor?


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Contents

• Mengapa kita membutuhkan APK

• Konstruksi APK

• Macam-macam APK

• Proses Desain APK


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Apakah fungsi APK itu ?

• Untuk memperoleh aliran fluida padatemperatur yang tepat untuk proses berikutnya

•Untuk mengkondensasikan uap

• Untuk menguapkan fluida

• Untuk memanfaatkan panas buang

•Untuk pembangkitan daya


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Typical crude oil distillation

E2

E1

E3

E4

E5 E6

E2

E5

Storage

Kerosene

Desalter

Top pump

around

Top pump

around

Naphtha

and gases

Kerosene

Furnace

Reduced crude

Light

gas oil

Heavy

gas oil

Reduced

crude

Heavy gas oil

Light gas oil

Bottom pumparound

D i s t i l l a t i o n t o w e r

Bottom

pump

around


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Geothermal Power cycle

Feedwater

heater


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Nuclear Power Plant


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Ocean Thermal Energy Conversion


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Heat utilities

• Hot utilities – Boiler generating service steam (maybe a combined

heat and power plant)

– Direct fired heaters (furnace)

– Electric heaters

• Cold utilities

– Cooling tower (wet or dry) providing service cooling

water

– Direct air-cooled heat exchanger


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Contoh sebuah APK

Bundle for shell-and-tube exchanger


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KATEGORI UTAMA ALAT PENUKAR KALOR

Heat exchangers

Recuperators Regenerators

Wall separating streams Direct contact

Kebanyakan Alat Penukar Kalor memiliki 2 aliranfluida, hot dan cold , tetapi beberapa memilikilebih dari dua aliran fluida


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Recuperators dan regenerators

Recuperative

Has separate flow paths for eachfluid which flow simultaneouslythrough the exchangertransferring heat between thestreams

Regenerative

Has a single flow path which the hotand cold fluids alternately passthrough.

Rotating wheel


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Compactness

• Can be measured by the heat-transfer area per unit volume or by channel size

• Conventional exchangers (shell and tube)have channel size of 10 to 30 mm givingabout 100m2/m3

•

Plate-type exchangers have typically 5mmchannel size with more than 200m2/m3

• More compact types available


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Compactness


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Double Pipe

Simplest type has one tube inside another - inner

tube may have longitudinal fins on the outside

However, most have a

number of tubes in the outertube - can have very many tubes

thus becoming a shell-and-tube


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Shell and Tube

Alat Penukar Kalor tipe shell and tube yang biasadigunakan pada industri proses


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Shell-side flow


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Baffle


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Complete shell-and-tube


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Plate-fin exchanger

• Made up of flat plates (parting sheets) andcorrugated sheets which form fins

• Brazed by heating in vacuum furnace


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Cooling Towers

•Large shell with packing at the bottom over whichwater is sprayed

• Cooling by air flow and evaporation

• Air flow driven by forced or natural convection

• Need to continuously make up the cooling water lost by evaporation


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Exchanger specification

• Heat load (duty) along with the terminal

temperatures of the streams

• Maximum pressure drop each streams – liquids - 0.5 bar

– gases/vapours below 2bar - 10% of inlet pressure

• Design pressures and temperatures

• Size/weight constraints

• Standards to apply

– General standards like ISO, TEMA, ASME, API etc – Companies own standards

• Other requirements


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The designer must supply an exchanger which

• Meets the stated specification

• Has reasonable initial costs and operating

costs (most exchangers are bought on the basis of the cheapest tender)

• Has a reasonable lifetime

– no damaging vibration – no thermal fatigue

– no unexpected fouling or corrosion


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Pemilihan Heat Exchanger

Choosing the best exchanger for a

given process application


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Langkah-langkah

• “Coarse filter” – Buang Jenis Alat Penukar Kalor yang

tidak memenuhi ketentuan tekanan dan

temperatur operasi, fluid-materialcompatibilitas, kondisi termal yang

extrem

• “Fine filter” – Estimasi Harga


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“Coarse filter”

• Use information on next few slides to reject

those exchangers which are clearly out of

range or are otherwise unsuitable• The information is summarised in the table

• At this stage, if in doubt, include the

exchanger (poor choices are likely to turnout expensive at the “fine filter” stage)


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Point-point utama

•

Tube /pipa dan cylinders dapat menahan tekananyang lebih besar dibanding dengan plates

• Jika APK dapat dibangun dengan material yang

bervariasi, berarti anda dapat menentukan metal

yang dapat tahan terhadap temperatur yang extremdan fluida-fluida yang korosif

• APK yang khusus hanya memiliki supplier yang

sangat sedikit, waktu pengiriman barang yang

lebih lama dan harus diperbaiki oleh orang yang

sangat ahli.


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Thermal effectiveness

T T T T

in out

in in

1 1

1 2

, ,

, ,

Stream temperature rise divided by the

theoretically maximum possible

temperature rise

T 1 ,in T 1 ,out

T 2 ,out T 2,in


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Double PipeTipe APK ini adalah yang paling simpel, memiliki satu tube di

dalam dan satu tube pada bagian luar, Tube paling dalam bisa

memiliki sirip secara longitudinal pada bagian luarnya

Walaupun demikian terdapat

pula jenis APK ini yangmemiliki beberpa tube didalam

tube luarnya.


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Double pipe

• Ukuran Normal

– 0.25 to 200m2

(2.5 to 2000 ft2

) per unit – Note multiple units are often used

• Built of carbon steel where possible


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Advantages/disadvantages of double-pipe

• Advantages

– Easy to obtain counter-current flow

– Can handle high pressure

– Modular construction

– Easy to maintain and repair

– Many suppliers

• Disadvantage

– Become expensive for large duties (above

1MW)

S f d bl i


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Scope of double pipe• Maximum pressure

– 300 bar(abs) (4500 psia) on shell side – 1400 bar(abs) (21000 psia) on tubeside

• Temperature range

– -100 to 600oC (-150 to 1100oF) – possibly wider with special materials

• Fluid limitations

– Few since can be built of many metals

• Maximum = 0.9

• Minimum DT = 5 K


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Shell and tube

• Size per unit 100 - 10000 ft2 (10 - 1000 m2)• Easy to build multiple units

• Made of carbon steel where possible


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Advantages/disadvantages of S&T

• Advantages

– Extremely flexible and robust design

– Easy to maintain and repair

– Can be designed to be dismantled for cleaning

– Very many suppliers world-wide

• Disadvantages

– Require large plot (footprint) area - often need

extra space to remove the bundle

– Plate may be cheaper for pressure below 16 bar

(240 psia) and temps. below 200oC (400oF)


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Scope of shell and tubeEssentially the same as a double pipe

• Maximum pressure – 300 bar(abs) (4500 psia) on shell side

– 1400 bar(abs) (21000 psia) on tubeside

•Temperature range – -100 to 600oC (-150 to 1100oF)

– possibly wider with special materials

• Fluid limitations

– Few since can be built of many metals

• Maximum = 0.9 (less with multipass)

• Minimum DT = 5 K


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Heat exchanger costing - “fine filter”

• Full cost made up of

– Capital cost

– Installation cost

– Operating cost

• The cost estimation method given here is basedonly on capital cost - which is the way it is often

done

• Note: installation costs can be as high as capital

cost except for compact exchangers

• Installation cost considerations can predominate

on offshore plant


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Quick sizing of heat exchangers

We estimate the area from

DT aDT b

A Q

U T

DWhere

D D

D D D

D D

T F T

T T T

T T

T m

m

a b

a b

ln( / )


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FT correction factor

• This correction accounts for the two streams not

following pure counter-current flow• At the estimation stage, we do not know the detailed

flow/pass arrangement so we use

– F T = 1.0 for counter flow which includes most compact and

double-pipe

– F T = 0.7 for pure cross flow which includes air-cooled and

other types when operated in pure cross flow (e.g. shell-and-

tube)

– F T = 0.9 for multi-pass

– F T = 1.0 if one stream is isothermal (typically boiling and

condensation)


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Estimating U

• This may be estimated for a given exchanger typeusing the tables

• These tables give U values as a function of Q/DT (the significance of this group will become clear

later)

• Example: high pressure gas cooled by treated

cooling water in a shell-and-tube, where

Q/DT = 30 000 W/Kgives U = 600 W/m2K

• This includes typical fouling resistances


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Estimating cost

• This has often been done by multiplying the

calculated area, A, by a “cost per unit area” • But, when comparing exchangers, U and A

vary widely from type to type. It is also

difficult to define A if there is a complicatedextended surface.

• Note, from our basic heat transfer equation

UA = Q / DT


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Steps in calculation

•Calculate

DT ln and hence estimate

DT

• Determine Q/DT

• Look up C value from table

– To determine C at intermediate Q/DT , use logarithmic

interpolation - see next slide

• Calculate exchanger cost from - Cost = C (Q/DT )

• Taking the last shell-and-tube example, C = 0.4.

Hence, Cost = £ 0.4 X 30 000 = £12 000• Make sure that you take account of footnotes in

tables


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Logarithmic interpolation

C ln C C C V V

V V

exp ( ) ln( / ) ln( / )

ln( / )1

1 2 1

1 2

ln(C 1)

ln(C 2)

ln(C )

ln(V1) ln(V) ln(V2)

Where the V s are the values of Q/ T. V 1 and V 2

are the values either side of the required value V


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Desain Termal

Alat Penukar Kalor


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Harga Lokal dan harga rata-rata

• “Overall” artinya dari “the hot side” ke “ the

cold side” termasuk semua termal resistan

• Titik khusus pada alat penukar kalor adalah local

• Jadi kita memiliki lokal, overall coefficient

LOKAL

KESELURUHAN ALAT PENUKA KALOR

mT mT T AU Q

T U q

D

D


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Q = U A DTk

Thot

Tcold

1 1 1

U r

yr

cold

cold w

w

hot

hot

yw


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Definisi dari harga rata-rata (mean values )

Dari slide sebelumnya

Bandingkan dua sides

Q

T U A

dQT

UdA

T

m

m T

Q AT T

D

D

1 1

D DT Q

dQ

T m T Q

U A

UdAmT AT

1


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Kasus Khusus dimana Ts linear terhadap Q

• Eqn. integrates to

give log. mean

temperaturedifference - LMTD

DT a

D D D D

D DT T

T T

T T m LM

a b

a b

ln( / ) DT b

Q

T e m p e r a

t u r e


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Pararel Flow


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Counter Flow


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Cross Flow

M lti h


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Multipass exchangers

• Untuk single-phase duties,Faktor correction teoritis,

F T , sudah diturunkan (lihar

referensi)

• Harga F T Kurang dari 1

• Jangan Merancang untuk F T

kurang dari 0.8

Q

T e m p .

T 1

T 2

t 1

t 2

D DT F T m T LM


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Thermal effectiveness

T T T T

in out

in in

1 1

1 2

, ,

, ,

Stream temperature rise divided by the theoretically

maximum possible temperature rise

T 1 ,in T 1 ,out

T 2 ,out T 2,in


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Tube layouts

• Typically, 1 in tubes on a 1.25 in pitch or 0.75 in

tubes on a 1 in pitch• Triangular layouts give more tubes in a given shell

• Square layouts give cleaning lanes with close pitch

pitchTriangul

ar

30o

Rotated

triangul

ar

60o

Squar e

90o

Rotate

dsquare

45o

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