(4-2-3) NPTEL - Properties of Cryogenic Fluids

8/22/2019 (4-2-3) NPTEL - Properties of Cryogenic Fluids

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Overview of Earlier LectureOverview of Earlier Lecture

Hydrogen

Helium

2Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay

Phase Diagram of Helium

Super fluid Helium


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Outline of the LectureOutline of the Lecture

Uses of Helium 4

Thermomechanical, Mechanocaloric,Fountain, Rollin Film Effects.

Sound Propagation in Super fluid

Helium 3 and Phase Diagram

Summary



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HeliumHelium 4 Phase Diagram4 Phase Diagram

LHe II, called as

super fluid, exhibitsproperties like zeroviscosity and largethermalre

Solid

-

conductivity.

It flows through

narrow slits andchannels veryrapidly.


Pressu

LHe-II

CriticalPoint

0 1 2 3 4 5 6 7

Lambda Point

Temperature, K

LambdaLine

Vapor


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HeliumHelium 44

Kapitza et al. stated

that viscosity forflow through thinchannels isinde endent of

3 0

4 0

icropoise

Normal viscosity

point

pressure drop and isonly a function oftemperature.


0 1 2 3 4 5 6 7

2 0

1 0

Vi

scosity,m

Total viscosity

Temperature, K


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The NMR (NuclearMagneticResonance) is usedby thepharmaceutical

Uses of HeliumUses of Helium 44rF Coil

Magneticscanning

coil


n us ry o s u ythe molecularstructure.

Sample

Sampletube

Magnet

LN2

LHe


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It has asuperconducting(SC) magnet (10 T~ 25 T) cooled byLiquid Helium bath.

rF Coil

Magneticscanning

coil

Uses of HeliumUses of Helium 44


The accuracy ofmeasurementincreases with the

field strength.

Sample

Sampletube

Magnet

LN2

LHe


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The MRI (MagneticResonance Imaging)machines are used forbody scanning.

Cryocooler 40K shield

20K



e magne s orboth NMR and MRImachines are cooled byLiquid Helium.LHe


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The Super conducting magnet systems at CERN

spanning over 27 Km radius are kept at 1.9 Kusing the Liquid Helium.

The low viscosit and hi h thermal conductivit


of Liquid Helium makes the system moreefficient.

Also, the engineering project ITER has

Superconducting magnets maintained at 4 K byLiquid Helium.


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Helium being a thin and inert gas, is used in leak

detection systems.

It is used as a shielding gas in arc welding torovide an inert atmos here.



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Liquid HeliumLiquid Helium -- IIII The peculiar properties of Liquid Helium II

give rise to interesting thermal and mechanical

effects as listed below.

Thermomechanical Effect

Mechanocaloric Effect

Fountain Effect

Rollin Film Effect



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Thermomechanical EffectThermomechanical Effect This effect was discovered in

the year 1938.

Consider a flask filled withsuper fluid helium (LHe II)and a heatin coil lacedT T+dT

dh

inside a differential containeras shown in the figure.

When the heat is applied to

the fluid in the inner container,the concentration of normalfluid increases.

heatcoil



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Thermomechanical EffectThermomechanical Effect The Super fluid component

tends to move towards this

region to equalize theconcentration.

Su er fluid bein less viscousT T+dT

dh

can flow rapidly through thenarrow channel.

Normal fluid being more

viscous, its flow is impeded bythe channel resistance.


heatcoil


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Thermomechanical EffectThermomechanical Effect As a result, due to the induced

pressure difference, a

pressure head called asThermo Mechanical PressureHead is developed.

T T+dT

dh

This head is proportionate tothe temperature rise of T inthe fluid.


heatcoil


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Mechanocaloric EffectMechanocaloric Effect It was discovered in the

year 1939.

The apparatus consists ofa round flask filled with afine owder and Su er

LHe II ResistanceThermometer

fluid Helium (LHe II).The flask has an openingat the bottom.

A resistance thermometeris mounted to detect thetemperature changes, asshown in the figure.

FinePowder

ColdLHe



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Mechanocaloric EffectMechanocaloric Effect The Super fluid Helium

(LHe - II) being less

viscous flows through thefine powder easily.

As a result the

LHe II ResistanceThermometer

concentration of normalfluid increases above thepowder.

Hence, the temperatureincreases inside the flask,which is sensed byresistance thermometer.


FinePowder

ColdLHe


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Fountain EffectFountain Effect

Fine

Consider an U-tube with afine capillary as shown in thefigure.

The U-tube is filled with a fine

LHe - IIFine

Powder

Heat

pow er an is immerse inSuper fluid Helium (LHe II)bath.

When heat is added to thepowder, the concentration ofnormal fluid increases due torise in the temperature.



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Fountain EffectFountain Effect

As a result, the Super fluidrushes in, to equalize the

concentration.

Normal fluid, being more

LHe IIspray

Fine

viscous cannot ow t rougthe fine powder.

The inflow of super fluid

builds up with time and finallysquirts out through the finecapillary opening at the top.


LHe - IIFine

Powder

Heat


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Rollin EffectRollin Effect This effect is named after Bernard

V. Rollin in the year 1937.

The Liquid Helium II exhibits aproperty of clinging to the walls ofthe container called as Cree in


effect.

The thickness of the film is in theorder of 30 nm.

Consider a test tube filled withLiquid Helium II as shown in thefigure.

LHe - II

Film


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Rollin EffectRollin Effect When the test tube is lowered into

the Liquid Helium - II bath, the

Rollin film clings to the tube andgradually fills the tube.

On the other hand if the tube is


raised above the bath level, itempties out slowly.

The ability of the fluid to flow

against gravity is called as Onneseffect.

LHe - II

Film


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Rollin EffectRollin Effect In these films, the capillary forces

dominate the gravity and viscous

forces.

The rate of flow is independent of


difference in level. It increaseswith drop in temperature.

It is zero at lambda point andbecomes constant below 1.5 K.

LHe - II

Film


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Rollin EffectRollin Effect This creeping behaviour added to

leaking ability of Helium II,

makes containment of LHe II toan enclosure difficult.


to be designed properly otherwiseHelium II creeps to the warmerside through valves and openingsand will evaporate.

LHe - II

Film


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Sound PropagationSound Propagation In LHe II, at least three different mechanisms

of sound can be propagated.

For temperatures above and below lambda point,propagation of ordinary sound which is nothing


u pressure an ens y osc a ons occurs.

This is called as First sound.


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Sound PropagationSound Propagation Below the lambda point temperature, the Liquid

Helium has LHe- I (normal fluid) and LHe II

(super fluid) components.

Due to difference in concentrations of these


u s, ere ex s s a empera ure gra en . sgradient causes oscillations of Normal fluid andSuper fluid which are called as Second sound.

The velocity of Second sound varies from zero atlambda point to 239 m/s at near 0 K.


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Sound PropagationSound Propagation In thin films, the LHe I component clings to

the walls due to the viscous effects.

If only the super fluid component in Secondsound oscillates, then it is called as Third sound.


This wave motion appears as an oscillation in thethickness of the film. The velocity of propagationof Third sound is around 0.5 m/s.

Another form of sound called as Zero sound hasbeen detected recently. The research is on tostudy its characteristics.


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Helium NomenclatureHelium Nomenclature

Isotopes

TempLHe I


e um

Helium 3

LHe II


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HeliumHelium 33Helium 3

It is a non radioactive isotope with two protons

and one neutron.

Normal Boiling Point K 3.19

-


Critical Pressure MPa 0.117Critical Temperature K 3.32

Liquid He 3 Density kg/m3 58.9

Latent Heat kJ/kg 8.49


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HeliumHelium 33 In 1920, Aston discovered another isotope of

Helium, He3. First liquefaction of Helium 3 was

achieved by Sydoriak et. al. in the year 1948.

This isotope He - 3 is very rare and is difficult to .


Isotope Relative %

He 4 ~100

He 3 1.3 x 10-4


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HeliumHelium 33 From the adjacent figure,

it is clear that for a given

pressure Liquid He - 3 ismore colder than LiquidHe 4.

100

1000

-mmH

g

He 3

He 4

0 0.5 1 1.5 2 2.5 3.0 3.5

10

1Pressure

Temperature, K29Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay

0.01


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HeliumHelium 3 phase diagram3 phase diagram

From the adjacentfigure

Saturated solid line.sure

Solid

Saturated vapor line.

Critical point.


Pre

s

Liquid

Vapor

Critical

Point

Temperature, K


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LHe - 3 (like LHe - 4)remains liquid under itsvapor pressure up toabsolute zero.

sure

Solid

It must be compressedto 28.9 bar at 0.32 K tosolidify.


Pre

s

Liquid

Vapor

Critical

Point

Temperature, K


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Helium 3 has notemperature andpressure at which solid- liquid vapor can co-exist. It means that its

ure

Solid

has no triple point.

Liquid He - 3 undergoesa different type of super

fluid transition atapproximately 3.2 mK.


Pre

s

Liquid

Vapor

Critical

Point

Temperature, K


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HeHe 3 & He3 & He 4 Mixture4 Mixture The line shown in the

adjacent figure is a

function ofconcentration of He 3.

e,

K

LambdaLine

Super fluid He I

1 . 5

by addition of smallamounts of He 3.

The mixture of He 3

and He 4 is notcompletely miscible atvery low temperature.

T

emperatu

r

Phase

SeparationRegion

0 0 . 2 0 . 4 0 . 6 0 . 8 1

He II

0 . 5

1 . 0

Mole fraction He -333Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay


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HeHe 3 & He3 & He 4 Mixture4 Mixture The mixture of He 3

and He 4 separate

below 1 K due to thedifferences in isotopicmass.

e,

K

LambdaLine

Super fluid He I

1 . 5

Separation occurs intoSuper fluid (rich in He -4) and Normal fluid(rich in He - 3).

T

emperatu

r

Phase

SeparationRegion

0 0 . 2 0 . 4 0 . 6 0 . 8 1

He II

0 . 5

1 . 0



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HeHe 3 & He3 & He 4 Mixture4 Mixture The point of intersection

of Lambda line and

phase separation regionis called as Tricriticalpoint (TCP).

e,

K

LambdaLine

Super fluid He I

1 . 5

The TCP at 0.872 K andwith a concentration of0.669 of He 3.

T

emperatu

r

Phase

SeparationRegion

0 0 . 2 0 . 4 0 . 6 0 . 8 1

He II

0 . 5

1 . 0


TCP


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HeHe 3 & He3 & He 4 Mixture4 Mixture

This separation into twoliquid phases anddifference in vaporpressure forms thebasis for Dilutione

,K

LambdaLine

Super fluid He I

1 . 5

Refrigerator.


T

emperatu

r

Phase

SeparationRegion

0 0 . 2 0 . 4 0 . 6 0 . 8 1

He II

0 . 5

1 . 0

Mole fraction He -3


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It is mostly used in Dilution refrigerators toachieve low temperatures.

It is also used as working fluid in Cryocoolers.Temperature close to 1 K are reported with Pulse



.

The properties are of interest in relation to thetheories of quantum statistical mechanics.

It is an important isotope in instrumentation forneutron detection.


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SummarySummary The summary of the topics covered are

Introduction to Cryogenics

Properties of Cryogens, T s Diagram

Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay 38

Hydrogen

Helium

Super fluid Helium

Helium - 3


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A self assessment exercise is given afterthis slide.

Kindly asses yourself for this lecture.



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Self AssessmentSelf Assessment

1. The pressure head in Mechanocaloric effect isproportional to _________________.

2. In Thermomechanical effect, ___________ fluidflows out of fine powder.

3. The viscosity of Super fluid helium is _________than normal fluid.

4. At a given pressure, the temperature of LHe 3is __________ than LHe 4.



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Self AssessmentSelf Assessment

5. Boiling point of LHe 3 is _______

6. Principle of Dilution Refrigerator is _________

7. ___________ isotope of Helium is difficult to

separate & also mention the temperature.

8. Second sound is due to the oscillations of __________

9. The speed of Third sound in LHe II is ________



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Self AssessmentSelf Assessment10. The thickness of Rollin film is in the order of

___________

11. The Tricritical point occurs at __________temperature.

12. Phase separation in He- 3 and He -4 Mixtureoccurs below ____________ Temperature.



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AnswersAnswers1. Rise in temperature

2. Super fluid helium (LHe II).3. Greater


.

5. 3.19 K

6. The separation that occurs below 0.8 K.

7. He 38. Normal fluid and Super fluid Helium

9. 0.5 m/s


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AnswersAnswers10. 30 nm

11. 0.872 K12. 1 K



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(4-2-3) NPTEL - Properties of Cryogenic Fluids

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