At13 Cryogenic

8/23/2019 At13 Cryogenic

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D e p a r t m e n t o f E n g i n e e r i n g P h y s i c s , F a c u l t y o f E n g i n e e r i n g , G a d j a h M a d a U n i v e r s i t y

( S t u d y P r o g r a m s o f E n g i n e e r i n g P h y s i c s & N u c l e a r E n g i n e e r i n g )

J l . G r a f i k a 2 , Y o g y a k a r t a 5 5 2 8 1 , ( + 6 2 2 7 4 ) 5 8 0 8 8 2 , h t t p : / / w w w . t f . u g m . a c . i d /

D e p a r t m e n t o f E n g i n e e r i n g P h y s i c s , F a c u l t y o f E n g i n e e r i n g , G a d j a h M a d a U n i v e r s i t y

( S t u d y P r o g r a m s o f E n g i n e e r i n g P h y s i c s & N u c l e a r E n g i n e e r i n g )

J l . G r a f i k a 2 , Y o g y a k a r t a 5 5 2 8 1 , ( + 6 2 2 7 4 ) 5 8 0 8 8 2 , h t t p : / / w w w . t f . u g m . a c . i d /

Joule-Thomson Experiment

-AT-

UGM

DepartmentofEngineeringPhysics,

FacultyofEngineering

StudyProgramsofEngineeringPhysics&NuclearEngineering

Compressibility Factor

Definition

a measure of deviation from

ideal gas behavior

approaches unity at low

pressures

Z for real gases is correlated in

terms of reduced pressure andreduced temperature

2

RT

pv

pRT

v

v

vZ actualactual

ideal

actual===

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Model Gas Real

Perbedaan dengan model gas ideal

o Volume molekul memperkecil ruang gerak bebas molekul.

o Antar molekul terjadi interaksi.

Salah satu cara untuk modifikasi dari gas ideal adalah

dengan menetapkan Faktor gas real.

dengan:

RT

pvZ =

( ) ( ) ( )L++++=

321

v

TD

v

TC

v

TBZ

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Persamaan van der Waals

Persamaan keadaan dari van der Waals

dengan a, b: konstanta karakteristik dari gas

o b: Kovolume

o a: Tekanan kohesi, merupakan koreksi dari penurunantekanan gas ke dinding akibat adanya gaya interaksi antarmolekul.

( ) RTbvv

ap =

+

2

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yProgramsofEngineeringPhysics&NuclearEngineering

Diferensial Total

Difenrensial total dari suatu fungsi f(x,y)

dyy

fdx

x

fdf

xy

+

=

xyyxx

f

yy

f

xxy

f

yx

f

=

=

22

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Persamaan Gas

Entalpi:

Energi internal:

dpT

vTvdTcdh

p

p

+=

dvpT

pTdTcdu

v

v

+=

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Joule Experiment

g a s .i d e a la nf o ro n l y f ( T )Ui . e . ,

g a s .i d e a la nf o r0

V

U

h e n c e

0d T&0d U

,e x p e r i m e n tsJ o u l e 'F r o m

d V

V

U

d T

T

U

d U

U .e n e r g y ,i n t e r n a li nc h a n g e aw i t h o u ts od o e si te x p a n d e di s

g a s )( i d e a lg a sp r e s s u r e l o w aw h e n

TCq&0w

wqU

0pa tb u l b t h ei n t o e x p a n d si t&g a st h eo fp r e s s u r e :p

0T,0pl i m

T

TV

V

21

b a t h1

=

=

==

+

=

==

+=

=

=

7

Measurement of the change in internal energy when a gas expandsisothermally.

The heat absorbed by the gas is proportional to the change in temperatureof the bath.

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Joule Thomson Experiment

The gas expands through theporous barrier, which acts as athrottle, and the whole apparatusis thermally insulated.

This arrangement corresponds toan isenthalpic expansion(expansion at constant enthalpy).

Whether the expansion results ina heating or a cooling of the gasdepends on the conditions.

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Joule Thomson expansion

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The pistons represent the upstream anddownstream gases, which maintain constantpressures either side of the throttle.

The transition from the top diagram to thebottom diagram, which represents thepassage of a given amount of gas through thethrottle, occurs without change of enthalpy.

)ci s e n t h a l p i(0H

VpVpd Vpd Vpw&0q

VpVpwqH

:m i c s t h e r m o d y n a o fl a w F i r s t

)P V(UH

P VUH

2211

V

0

2

0

V

1

1122

2

1

=

===

++=

+=

+=

Q

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Joule-Thomson Coefficient

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JT

H

TpH

T

p

Tp

p

T

pH

CpT

dpp

HdTC

cisenthalpifor

dpp

HdT

T

HdH

pTH

=

=

+=

+

=

1

0

),(

0

0

onlyf(T)Hgas,idealFor

=

=

T

T

p

H

gasrealfor

p

H

Joule-Thomson Coefficient

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Apparatus Measurement of the isothermal Joule-Thomson

coefficient (JT) is given below.

The electrical heating required to offset the cooling

arising from expansion is interpreted as Hand usedto calculate (H/p)T, which is then converted to .

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Inversion The sign of the Joule-Thomson coefficient, ,

depends on the conditions. Inside the boundary, the shaded area, it is

positive and outside it is negative. The temperature corresponding to the

boundary at a given pressure is the `inversiontemperature' of the gas at that pressure.

For a given pressure, the temperature mustbe below a certain value if cooling is requiredbut, if it becomes too low, the boundary iscrossed again and heating occurs.

Reduction of pressure under adiabaticconditions moves the system along one of theisenthalps, or curves of constant enthalpy.

The inversion temperature curve runs throughthe points of the isenthalps where their slopeschange from negative to positive.

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Inversion

The inversion

temperatures for

three real gases,nitrogen, hydrogen,

and helium.

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Pencairan Gas

Penentu aplikasi teknik pencairan gas adalah titik

kritis.

Gas NH3 dikompresi menjadi 10 bar, didinginkandengan suhu lingkungan dan diekspansikan.

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Udara

Titik kritis pada suhu -147C

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Proses Linde

Secara bertingkat,

udara dikompresi

isotermal,kemudian

didinginkan

dengan aliranberlawanan

dengan udaralebih dingin yang

belum mencair.

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Linde refrigerator The gas is recirculated

and, so long as it isbelow its inversiontemperature, it cools onexpansion through thethrottle.

The cooled gas coolsthe high-pressure gas,which cools still furtheras it expands.

Eventually liquefied gasdrips from the throttle.

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Claude liquefaction process

Replace the throttle valve by

an expander:

o Gas expander saturated orslightly superheated vapor cooled and throttled to produceliquefaction (as in the Lindeprocess) unliquefied portionmixes with the expander exhaustand returns for recycle.

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Liquefaction processes

Common use for:

o Liquid propane as a domestic foil

o Liquid oxygen in rocketo Liquid natural gas for ocean transport

o Liquid nitrogen for low temperature refrigeration

o Gas mixture are liquefied for separation

Cooled to a temperature in the two-phase region:

o By heat exchanger at constant pressure

o By an expansion process from which work is obtained

o By a throttling process

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At13 Cryogenic

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