Various methods are used engineering for heating and expanding the Gases.these methods are also applicable to the contraction or cooling of gases.The contraction means negative expansion and cooling means negative heating.
01)Constant Volume Process:-
There will be no change in Volume and no external work will be done by the gas,when a Gas is heated in a fixed enclosed space.Due to heating,Pressure and Temperature will rise and the whole heat supplied will be stored in the form of Internal Energy.
02)Constant Pressure Process:-
When a Gas is heated at constant Pressure,the Volume and the Temperature of a Gas will increase.There will be some external work done due to increase in Volume.
03)Constant Temperature Process:-
This is also known as "Isothermal Process".When a heat is supplied to a gas at constant Temperature,the expansion occurred is called "Isothermal Expansion".The whole of the heat supplied to the Gas will be used up in doing external work.
When a Gas is heated in such a way that its Pressure multiplied by its Volume remain constant,the expansion called "Hyperbolic".
PRESSURE x VOLUME= CONSTANT.
The workdone and the heat supplied are same.This identical only in the case of Perfect Gas and not for vapours.
05)Reversible Adiabatic Process:-
This is also called as "Isentropic Process".The system neither receives nor gives out heat to the surrounding.This means no exchange of heat between the system and the surrounding.
This process follows the general Law ( PRESSURE x VOLUME raise to n equals to Constant) where the index "n" may have any value depending upon the method of carrying out expansion.
This is said to be occurred,when a fluid suddenly expands into a Vacuum Chamber through an Orifice of large dimension.No heat is supplied or rejected,there is no workdone and the Temperature during this process remains constant.
This type of expansion occures when a Gas or vapour is expanded through an Aperture of minute dimension like a valve which is very slightly opened or a narrow throat.In Throttling Process,if it is a perfect gas ,there is no change in Temperature.