Hi Akilan,

to what I have understood in ideal system, isothermal expansion energy is the energy needed to expand the thermodynamic system by keeping the system's temperature constant (no change in internal energy). Suppose that the system is thermally isolated from its surroundings and if the system is allowed to expand quasi-statically under these adiabatic conditions then it performs work on its environment, its internal energy is suppressed, and its temperature is altered. Nonetheless, there is almost no ideal system in practical application.

An adiabatic expansion is a thermodynamic process, during which each elementary mass of working fluid has its specific volume increased without experiencing any heat transfer.

The adiabatic expansion is the one known as Joule Thomson Effect. In this case is called expansion due to a decompression from high to low temperature. The process is adiabatic in absence of shaft work. Depending on the thermodynamic properties of the substance the final temperature may increase or decrease. 

Dear Dr. Kwei,

I do agree that isothermal reflects a constant temperature condition. However, what I have written above is that the conditions, i.e. altered temperature and suppressed internal energy, can be found in adiabatic process (suppose that the system is thermally isolated, which means there is no heat transfer at the system's boundary, dQ = 0). I hope you also noticed that Mr. Akilan also asked about adiabatic expansion process.

Ruri