PROPERTIES-OF-CRYOGENIC-FLUIDS.pptx

1. PROPERTIES OF
CRYOGENIC LIQUIDS

2. Cryogen
 Fluid with normal boiling point less than 123 K.

6. Liquid Methane
 It boils at 111.7 K.
 It can be used as rocket fuel.
 In the form of Compressed natural gas (CNG).

7. Liquid Neon
 It is a clear, colorless liquid with boiling point at 27.1 K.
 Liquid neon is commercially used as cryogenic
refrigerant.
 It is compact, inert and less expensive as compared to
liquid helium.

8. Liquid Nitrogen (LN2)
 Boils at 77.36 K and freezes at 63.2 K.
 Resembles water in appearance - 807 kg/m3 (water –
1000 kg/m3).
 Exists in 2 stable isotopes - N14 & N15 in ratio of 10000:
38.
 Heat of vaporization is 199.3kJ (water -2257kJ/kg) and it
is produced by distillation of liquid air.
 Nitrogen is primarily used to provide an inert atmosphere
in chemical and metallurgical industries.

9. Liquid Nitrogen (LN2)
 It is also used as a liquid to provide refrigeration.
 Food preservation, blood, cells preservation.
 High temperature superconductivity.

10. Liquid Oxygen (LOX)
 Blue in color – due to long chains of O4.
 Boils at 90.18 K and freezes at 54.4 K.
 Has a density of 1141kg/m3 (water – 1000 kg/m3).
 O2 is slightly magnetic and exists in 3 stable isotopes - O16,
O17, and O18 in ratio of (10000: 4:20).
 Because of the unique properties of oxygen, there is no
substitute for oxygen in any of its uses –widely used in
industries and for medical purpose.
 It is largely used in iron and steel manufacturing industry.
 Oxidizer propellant for space craft rocket applications.

11. Liquid Argon
 It is a colorless, inert and non toxic gas.
 It boils at 87.3 K and freezes at 83.8 K.
 It has a density of 1394 kg/m3 (water – 1000 kg/m3).
 Exists in 3 stable isotopes – Ar35, Ar38, Ar40 and in a ratio
of (338 : 63 : 100000)
 The property of inertness of argon is used to purge
moulds in casting industry.

12. Liquid Argon
 It is used in Argon-oxygen decarburization (AOD) process
in stainless steel industry.
 It offers inert atmosphere for welding stainless steel,
aluminum, titanium etc

13. Liquid Air
For practical purpose, it is considered as a mixture of 78% N2
+ 21% O2 + 1% Ar + others.
 It has a boiling point of 78.9 K and 874 kg/m3 as density
(water density - 1000 kg/m3).
 Liquid air was earlier used as pre coolant for low
temperature applications.
 Liquid air is primarily used in production of pure
nitrogen, oxygen, and rare gases

14. Hydrogen
 Hydrogen exists in diatomic form as H2.
 Normal Boiling Point K 20.27
 Normal Freezing Point K 13.95
 Critical Pressure M Pa 1.315
 Critical Temperature K 33.19
 Liquid Hydrogen Density kg/m3 70.79
 Latent Heat kJ/kg 443
 It has three isotopes hydrogen, deuterium and tritium.

15. Hydrogen
 Tritium is radioactive and is unstable.
 The relative ratio of existence of hydrogen as
diatomic molecule (H2) and as Hydrogen Deuteride
(HD) is 3200:1
 Hydrogen exists in two molecular forms – Ortho and
Para.

16. Ortho and Para Hydrogen
 Spin is defined as the rotation of a body about its own axis.
 An H 2 molecule has 2 protons and 2 electrons.
 The distinction between the two forms of hydrogen is the
direction of the spin of protons.
 The two protons possess a spin which gives the angular
momentum.
 If the nuclear spins are in same direction for both the protons,
it is Ortho Hydrogen.
 If the nuclear spins are in opposite direction for both the
protons, it is Para Hydrogen.

18. Ortho and Para Hydrogen
 With the decrease in the temperature, the Ortho hydrogen is
converted to the Para hydrogen.
 At 300K Ortho 75% and Para 25%
 At 20K Ortho 0.179% and Para 99.821%
 Para form is a low energy form and therefore heat is liberated
during conversion.
 • Conversion of ortho to para form of hydrogen is an exothermic
reaction.
 • This conversion is a very slow process.
 • In order to make this conversion faster, catalysts are added

19. Liquefaction of H2:
 During liquefaction, the heat of conversion causes evaporation
of 70% of hydrogen originally liquefied. This is an important
constraint in liquefaction and storage of H2.
 Uses
 Cryogenic engines are powered by propellants like liquid
hydrogen.
 It is being considered as fuel for automobiles.
 Cryo coolers working on a closed cycle use hydrogen as working
fluid.
 Hydrogen codes and standards should be followed to ensure
safety while handling liquid

20. Helium
Evidence of Helium was first noted by Janssen during solar eclipse
of 1868. It was discovered as a new line in the solar spectrum.
 • In the year 1895, Ramsay discovered Helium in Uranium
mineral called as Clevite.
 • In the year 1908, K. Onnes at Leiden liquefied Helium using
Helium gas obtained by heating Monazite sand procured from
India
 Helium is an inert gas and exists in monatomic state.
 Normal Boiling Point K 4.25
 Normal Freezing Point NA

22. Helium
 Critical Pressure M pa 0.227
 Critical Temperature K 5.25
 Liquid Helium Density kg/m3 124.8
 Latent Heat kJ/kg 20.28
 In 1920, Aston discovered another isotope of Helium - He3 in
addition to He4.
 • Helium exists in two isotopes.
 1. He4 = 2 electrons, 2 protons + 2 neutrons.
 2. He3 = 2 electrons, 2 protons + 1 neutrons

23. Helium
 The percentage of He3 is 1.3 x 10-4 %. So mostly it is He4 (100
%)
 Helium has no temperature and pressure at which solid - liquid
– vapor can co-exist. It means that it has no triple point
 Saturated liquid Helium must be compressed to 25.3 bar to
solidify
 As Liquid Helium is further cooled below a particular
temperature (2.17K), a new liquid phase,
 LHe–II, emerges out.
 The two different liquids are called as LHe – I and LHe – II

25. Helium
 These liquid phases are distinguished on the basis of their
viscosity. ie
 LHe–I: Normal fluid
 LHe–II: Super fluid
 This phase separation line is called as Lambda Line
 The point of intersection of phase separation line with
saturated liquid line is called as Lambda Point.
 LHe – II is called as super fluid because it exhibits properties
like zero viscosity and large thermal conductivity.
 This fluid expands on cooling. Owing to its low viscosity, the
fluid below the lambda point, LHe – II, flows through narrow
slits and channels very rapidly.

27.  The variation of specific heat in Liquid Helium is abrupt
and posses a discontinuity at the lambda Point
 The point is called as lambda point because
shape of the curve resembles the Greek letter λ
 There is no energy involved in lambda transition

28.  Kapitza et al. stated that viscosity for
flow through thin channels is
independent of pressure drop and is
only a function of temperature.
 To explain this anomaly, a two fluid
model is used
SUPER FLUID HELIUM

29. Two fluid Model
 In the two fluid model, the liquid is
assumed to be composed of two fluids,
normal and super fluid.
 Mathematically,
 ρ = ρn + ρs
 ρ - total density
 ρn - normal density
 ρs – super fluid density.

30.  Temperature dependence of density below
lambda point.

31. Super fluid Helium
 Heat transfer in super fluid helium (LHe – II) is very special.
 When the pressure above LHe - I is reduced by pumping, the fluid
boils vigorously.
 During pumping, the temperature of liquid decreases and a part of the
liquid is boiled away.
 When T < λ point temperature, the apparent boiling of the fluid
stops.
 Liquid becomes very clear and quiet, even though it is vaporizing
rapidly.
 Thermal Conductivity of He – II is so large, that the vapor bubbles do
not have time to form within the body of the fluid before the heat is
quickly conducted to the surface

32. Uses Of HELIUM 4
 The NMR (Nuclear Magnetic Resonance) is used by the
pharmaceutical industry to study the molecular structure.
 It has a superconducting (SC) magnet (10 T ~ 25 T) cooled by
Liquid Helium bath.
 The accuracy of measurement increases with the field strength
 The MRI (Magnetic Resonance Imaging) machines are used for
body scanning.
 The SC magnets for both NMR and MRI machines are cooled by
liquid Helium.
 The Super conducting magnet systems at CERN spanning over 27
Km radius are kept at 1.9 K using the Liquid Helium.
 The low viscosity and high thermal conductivity of Liquid
Helium makes the system more efficient.

33.  The engineering project ITER has Superconducting magnets
maintained at 4 K by Liquid Helium.
 Helium being a thin and inert gas, is used in leak detection
systems.
 It is used as a shielding gas in arc welding to provide an inert
atmosphere

34.  The peculiar properties of Liquid Helium – II give rise to interesting
thermal and mechanical effects.
 Thermo-mechanical Effect
 Mechano-caloric Effect
 Fountain Effect
 Rollin Film Effect

35. Thermo Mechanical Effect
 This effect was discovered in the year 1938.
 Consider a flask filled with super fluid helium (LHe – II)
and a heating coil placed inside a differential container
 When the heat is applied to the fluid in the inner container,
the concentration of normal fluid increases.
 The Super fluid component tends to move towards this region to
equalize the concentration.
 Super fluid being less viscous can flow rapidly through the narrow
channel.

36. Thermo Mechanical Effect
 Normal fluid being more viscous, its flow is impeded by the channel
resistance.
 As a result, due to the induced pressure difference,
a pressure head called as Thermo Mechanical Pressure Head
is developed.
 This head is proportionate to the temperature rise of >T in
the fluid.

37. Mechano Caloric Effect
 It was discovered in the year 1939.
 The apparatus consists of a round flask filled with a fine powder
and Superfluid Helium (LHe – II).
 The flask has an opening at the bottom.
 A resistance thermometer is mounted to detect the temperature
changes,
 The Super fluid Helium (LHe - II) being less viscous flows through
the fine powder easily.
 As a result, the concentration of normal fluid increases above the powder.
 Hence, the temperature increases inside the flask, which is sensed by
resistance thermometer

38. Fountain Effect
 Consider an U-tube with a fine capillary as shown.
 The U-tube is filled with a fine powder and is immersed in
Super fluid Helium (LHe – II) bath.
 When heat is added to the powder, the concentration of
normal fluid increases due to rise in the temperature.

39. Fountain Effect
 As a result, the Super fluid rushes in, to equalize the
concentration.
 Normal fluid, being more viscous cannot flow through the
fine powder.
 The inflow of super fluid builds up with time and finally
squirts out through the fine capillary opening at the top.

40. Rollin Effect
 This effect is named after Bernard V. Rollin in the year 1937.
 The Liquid Helium – II exhibits a property of clinging to the wall
of the container called as Creeping effect
 The thickness of the film is in the order of 30 nm.

41. Rollin Effect
 Consider a test tube filled with Liquid Helium – II.
 When the test tube is lowered into the Liquid Helium - II bath, the
 Rollin film clings to the tube and gradually fills the tube.
 On the other hand, if the tube is raised above the bath level, it empties out
slowly.
 The ability of the fluid to flow against gravity is called
as Onnes effect.

42. Rollin Effect
 In these films, the capillary forces dominate the gravity and viscous
forces.
 The rate of flow is independent of height of flow or barrier and
difference in level.
 It increases with drop in temperature.
 It is zero at lambda point and becomes constant below 1.5 K.

43. Rollin Effect
 This creeping behaviour added to leaking ability of Helium – II,
makes containment of LHe – II to an enclosure difficult.
 The enclosure or the container has to be designed properly otherwise
Helium – II creeps to the warmer side through valves and openings
and will evaporate.

44. Sound Propagation
 In LHe – II, at least three different mechanisms of sound can be propagated.
 For temperatures above lambda point, propagation of ordinary sound which is
nothing but pressure and density oscillations occurs.
 This is called as First sound.
 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 fluids, there exists a temperature
gradient. This gradient causes oscillations of Normal fluid and Super fluid which
are called as Second sound.
 The velocity of Second sound varies from zero at lambda point to 239 m/s at near
0 K.

45. Sound Propagation
 In thin films, the LHe – I component clings to the walls due to the viscous
effects.
 If only the super fluid component in Second sound oscillates, then it is called
as Third sound.
 This wave motion appears as an oscillation in the thickness of the film. The
velocity of propagation of Third sound is around 0.5 m/s.
 Another form of sound called as Zero sound has been detected recently.
 The research is on to study its characteristics.

46. Helium - 3

47. Helium - 3
 It is a non radioactive isotope with two protons
and one neutron
 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 isolate from He – 4.

48.  For a given pressure Liquid He - 3 is more colder than Liquid He – 4.
 LHe - 3 (like LHe - 4) remains liquid under its vapor pressure up to absolute
zero.
 It must be compressed to 28.9 bar at 0.32 K to solidify.
 Helium – 3 has no temperature and pressure at which solid- liquid – vapor can
coexist.
 It means that it has no triple point.
 Liquid He - 3 undergoes a different type of super fluid transition at
approximately 3.2 mK.

49. Uses
 It is mostly used in Dilution refrigerators to achieve low temperatures.
 It is also used as working fluid in Cryocoolers.
 Temperature close to 1 K are reported with PulseTube Cryocooler.
 The properties are of interest in relation to the theories of quantum
statistical mechanics.
 It is an important isotope in instrumentation for neutron detection.