liquefaction of gasesiquefaction of gases ,adiabatic expansion ,mechanical work ,demagnetization of paramagnetic substance ,adiabatic demagnetization

1. Liquefaction of gases
(adiabatic expansion involving
mechanical work)
CECH-202
UNIT-1
BY - Ms MAYURI R SOMPURA

2. 2. Adiabatic expansion:-
• When a gas is made to expand against a pressure, as in an engine, it
does some external work at expense of kinetic energy which decreses
and as a result cooling occurs.
• This principle combined with J.T. effect hs been used in Claude’s
process for liquefaction of air.
• George claude was a French engineer.
➢Production of low temperature by adiabatic demagnetization of a
paramagnetic substance.
BY - Ms MAYURI R SOMPURA

3. ➢ Production of low temperature by adiabatic
demagnetization of a paramagnetic substance:-
• very low temperatures in the vicinity of absolute zero have have been
obtained by :
I. Joule – Thomson expansion of hydrogen
II. Using liquid helium
III. Making use of magnetic properties of paramagnetic substances
(salts of rare earths )
• The paramagnetism of these substances is due to presence of odd
(unpaired) electrons.
BY - Ms MAYURI R SOMPURA

4. ➢ Production of low temperature by adiabatic
demagnetization of a paramagnetic substance:-
• The method of adiabatic demangnetization of a paramagnetic
substance was first suggested in 1926 by P. Debye and independently
by W. F Giauque in 1927.
• It is based on the fact that the temperature of thermally isolated
paramagnetic substance drops when it is demagnetized.
• It can be understood from the following equation for a magnetic
system :
• 𝑑𝑆 =
𝐶𝐵 𝑑𝑇
𝑇
+ 𝐸˳𝑉
𝜕𝑀
𝜕𝑇
𝑑𝐵
BY - Ms MAYURI R SOMPURA

5. ➢ Production of low temperature by adiabatic
demagnetization of a paramagnetic substance:-
• 𝑑𝑆 =
𝐶𝐵 𝑑𝑇
𝑇
+ ℇ˳𝑉
𝜕𝑀
𝜕𝑇
𝑑𝐵
• Where :
M = extent of magnetization in presence of external magnetic field
B = external magnetic field
V = volume ℇ˳ = 𝑝𝑒𝑟𝑚𝑖𝑎𝑏𝑖𝑙𝑖𝑡𝑦
CB = heat capacity of the system at constant magnetic field B
BY - Ms MAYURI R SOMPURA

6. ➢ Production of low temperature by adiabatic
demagnetization of a paramagnetic substance:-
• The extent of magnetization of a paramagnetic substance at constant
magnetic field always decreases with the increase in temperature
• Hence partial derivative
𝜕M
𝜕T
B is always negative.
• When substance is demagnetized reversibky and adiabatically we get,
•
𝑑𝑇
𝑇
= − ℇ˳
𝑉
𝐶𝐵
𝜕𝑀
𝜕𝑇
𝑑𝐵
• dT/T is negative so dT is also negative
• Thus, a paramagnetic substance cools down upon adiabatic
demagnetization
BY - Ms MAYURI R SOMPURA

7. assignment
• Write a note on – liquefaction of gases with respect to adiabatic
expansion
BY - Ms MAYURI R SOMPURA