Thermodynamic Process

As we know that a system itself does not undergo any change. Rather, the state of the system changes. Thus, whenever a system undergoes a change in its state, the line joining the series of intermediate states through which the system has passed is called a path. And when this path is fully specified then it is called "Thermodynamic Process". 
When there is an interaction between the system and the surrounding, the state of the system changes from one equilibrium to another. And these changes in the state of the system can be fast or slow and large or small.
"Initial and Final states are equilibrium states"

Classification Based On State Variable
Thermodynamic can be described by its pressure, temperature and volume, etc. These are the state variables of a system. 
"A process by which two or more of these variables can be changed is called a thermodynamic process".
When state variables change, the state of the system also changes. By keeping one of these three variables constant and changing the remaining two variables, the state of the system can be changed. 
For example, by keeping the temperature constant, changing the pressure and volume, the state of the system can be changed. 
On this basis (keeping one of the three variables constant), thermodynamic processes are generally of four types. These are namely "Isobaric, Isochoric, isothermal and Adiabatic processes". 
There are three other types of processes that we are studying along with these types and these are "Polytropic, Isentropic and Throttling process". 

Isothermal Process
When the state of a system changes from one equilibrium state to another keeping the temperature constant, the system undergoes an isothermal process (Or We can say that "there is no change in the temperature of the system in isothermal process"). 
For Example- 
1) Latent heat of vaporization is an example of isothermal process because when we heat water at 100°C, it will not start boiling immediately. It will continue to absorb heat at a constant temperature and only after absorbing this heat, water will get convert to steam at constant temperature.
2) Latent heat of freezing at constant temperature (or water converted into ice)

➝ When a thermodynamic undergoes a change in its state at constant temperature, the change is said to be Isothermal change. The condition of Isothermal change is given by, "dT=0"
In an isothermal process; 
                ஃ   ∆T＝ (T₂-T₁) ＝ 0
          Hence,  [ P₁V₁ ＝ P₂V₂ ]

Isobaric Process
When the state of a system changes from one equilibrium state to another keeping the pressure constant, the system undergoes isobaric process (Or We can say that "there is no change in the pressure of the system in isobaric process"). In practical, ideal constant pressure can not be achieved.
➝ In an isobaric process,  
                ஃ ∆P＝ (P₂-P₁) ＝ 0
          Hence,  [V₁/T₁ ＝ V₂/T₂]

Isochoric Process
When the state of a system changes from one equilibrium state to another keeping the volume constant, the system undergoes isochoric process (Or We can say that "there is no change in the volume of the system in isochoric process").
For example- Heating of a gas in a closed cylinder is an example of isochoric process
➝ In an isochoric process, 
                ஃ ∆V＝ (V₂-V₁) ＝ 0
           Hence,  [ P₁/P₂ ＝ T₁/T₂ ]

Adiabatic Process
The adiabatic process is defined as a process in which there is no heat transfer between the system and the surrounding.
      In the adiabatic process, there is no interaction between the system and the surroundings in the form of heat, but still they interact when the state of the system changes from one equilibrium state to another. Wherever, the state of a system changes from one equilibrium state to another keeping the heat constant, the system undergoes an "Isothermal Process".
(Or We can say that "there is no change in the system's heat in adiabatic process").
➝ In an adiabatic process,  
                 ஃ ∆Q ＝ (Q₂-Q₁) ＝ 0

Polytropic Process
Any thermodynamic process that can be described by the following expression is referred to be a polytropic process;
P(V)ⁿ = Constant
Here,
      Exponent n is known as the polytropic index and it may take any value between 0 to infinity.

Isentropic Process
An Isentropic process is a process in which the entropy of the system remains unchanged when the system changes their state from one equilibrium state to another. It is also called as constant entropy process. It is both Adiabatic and reversible in nature. There is no transfer of heat or matter.

Throttling Process
A thermodynamic process called throttling process when the enthalpy of a gas or medium stays constant. In this, "A high-pressure fluid is converted into low-pressure fluid by using a throttle valve". It is also known as "Joule-Thomson Expansion".
During a throttling process, no heat is added and no work is done by or on the system. And internal energy of the gas also remains the same. These processes are irreversible in nature. 
Hence,
ஃ  dW = dQ = 0
Since throttling process is isentropic, and for an ideal gas enthalpy is a function of temperature only. Thus, the temperature of an ideal gas does not change during a throttling process.
THROTTLING VALVE
It is a type of flow restricted device that can cause a significant pressure drop in fluids. These pressure drops is often accompanied a large drop in temperature 


Hope you have found this article helpful!!
Let me know what you think about THERMODYNAMICS PROCESSES. Feel free to comment if you have any queries.!!

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