Low Temperature Physics-II S. Y. B. Sc.

Joule-Thomson Effect It is also known as porous plug expt. The porous plug made up of silk or cotton wool

Joule-Thomson Expt.

When a gas allowed to flow through the plug from upper to lower portion, it faces large drop in pressureP1>>>P2,. While the temperature of lower portion is maintained constant at T1 with the help of constant temperature bath, the temperature of the upper portion has nothing to do with that path because of thermal insulation.

Throttling Process A process in which a gas allowed to expand slowly as it pass from a constant higher pressure to a constant lower pressure state is called throttling process.

throttling process A porous plug divides an adiabatic cylinder into two parts and both the parts have adiabatic piston fitted from two ends. piston adiabatic walls porous plug In this experiment work is obviously done. The pressures are kept constant. đ đ From the definition of enthalpy

Results:- If the initial temperature is sufficiently low, all the gases suffer a fall of temperature (cooling) on expansion due to their passage through the plug. That is T2<T1. The drop in the temperature (cooling) is proportional to the drop in pressure. As the initial temperature T1 is increased, the drop in temperature becomes smaller and a particular value of T1 say Ti, the drop becomes zero. There is neither cooling nor heating. Finally, if the initial temperature has a value above T1, the gas actually heated up instead of getting cooled.

Isenthalpic curve and inversion curve On P-V diagram we get series of discrete points which indicate the final equilibrium state with enthalpy. the smooth curve joining these points as known as Isenthalpic curve. It is Highly reversible Process Between state 1 and 4 – heating of gas Between state 4 and 7 – gas cools down

Relation between Inversion, Boyle and critical Temperature