(4-2-3) NPTEL - Properties of Cryogenic Fluids
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Transcript of (4-2-3) NPTEL - Properties of Cryogenic Fluids
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44
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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
3Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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.
4Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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.
5Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
6Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
7Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
Uses of HeliumUses of Helium 44
8Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
e magne s orboth NMR and MRImachines are cooled byLiquid Helium.LHe
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Uses of HeliumUses of Helium 44
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
9Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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Uses of HeliumUses of Helium 44
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.
10Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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
11Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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
12Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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.
13Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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.
14Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
15Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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.
16Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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.
17Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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.
18Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
19Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
20Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
21Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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.
22Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
23Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
24Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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.
25Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
26Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
-
27Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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 .
28Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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.
30Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
Pre
s
Liquid
Vapor
Critical
Point
Temperature, K
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HeliumHelium 3 phase diagram3 phase diagram
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.
31Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
Pre
s
Liquid
Vapor
Critical
Point
Temperature, K
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HeliumHelium 3 phase diagram3 phase diagram
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.
32Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
Mole fraction He -334Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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
Mole fraction He -335Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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.
36Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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
Uses of HeliumUses of Helium 33
37Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
.
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.
39Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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.
40Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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 ________
41Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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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.
42Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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AnswersAnswers1. Rise in temperature
2. Super fluid helium (LHe II).3. Greater
43Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
.
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
44Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
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45Prof. M D Atrey, Department of Mechanical Engineering, IIT Bombay
an ouan ou