Liquid Hydrogen

SESM3037

Ortho-para ratio

ratio of number of molecules occupying odd & even energy levels

State Function

Path independent measurable quantity dependent on current state and not history

Free energy

portion of internal energy converted to work, excluding heat content

Internal Energy

energy contained within system

Helmholtz Free Energy

free energy available for work at constant temperature and volume

Gibbs Free Energy

Maximum work done at constant temperature and pressure

Inversion Temperature

Temperature at which the Joule-Thompson coefficient changes sign

Inversion Temperature of Helium

43 K

Inversion Temperature of Hydrogen

202 K

Inversion Temperature of Air

603 K

Inversion Temperature of Nitrogen

623 K

Inversion Temperature of Oxygen

761 K

Triple Point of Nitrogen

63 K

Triple point of Hydrogen

14 K

Hydrogen Ortho-Para ratio at room temperature

3:1

Hydrogen ortho-para ratio at 80 K

1:1

Hydrogen ortho-para ratio at 20 K

100% para

Hydrogen Boiling Point

20 K

Advantages of Claude Cycle

Isentropic expansion of gas results in a lower temperature vs isenthalpic expansion in LH cycle.

Does not require pre-cooling or JT valve.

Examples of State Functions

P, T, V, s

Examples of Path Functions

U, H, F, G

Spin of Para Hydrogen

Antisymmetric

Spin of Ortho Hydrogen

Symmetric

Inversion Temperature of Neon

260 K

Van der Walls Pressure Term

a

Van der Walls Volume Term

b

Nitrogen Boiling Point

77 K

Negative Yield

System will not ‘start up’ with working gas warmed up after JT valve expansion

Requirement of LH cyce

Pre cooling required due to hydrogen’s inversion temperature of 202 K requiring a cryogenic liquid coolant

Liquid Yield

Ratio of work per unit compressed to work per unit liquified

Ortho Hydrogen Species

aa, ab+ba, bb

Para Hydrogen Species

ab-ba

Ortho-Para heat conversion

Heat conversion higher than heat for vaporisation