We were discussing various basic concepts of thermodynamics such as “Thermodynamics point and path functions” in our recent post. We have also discussed the "concept of entropy" and "Perpetual motion machines" in the field of thermal engineering.

Today we will see here the concept of isolated system and non-isolated system used in thermodynamics with the help of this post.

### Let us first see here isolated system in thermodynamics

A system will be termed as an isolated system in thermodynamics, if there will not be any transfer of mass or transfer of energy i.e. heat energy or work energy across the system boundary.

In simple words we can say that, there will not be any interaction between system and surrounding.
Therefore, for an isolated system, change in system energy will be zero.  Hence, isolated system could be considered as fixed or constant energy system because there will not be any transfer of energy or transfer of mass across the system boundary and energy of system will be remaining constant.
Therefore, for an isolated system, we will have following condition
dW = 0 and dQ = 0
Let us recall the first law of thermodynamics and apply here for an isolated system and we will have following equation i.e.
dE =0
We can say from above equation, we can say that system energy will be constant for an isolated system in thermodynamics.

### Non- isolated system in thermodynamics

There are two types of non-isolated system in the field of thermal engineering and these are closed system and open system.

#### Open system

In case of open system in thermodynamics, mass transfer across the system boundary will take place and energy may also transfer across the system boundary. You will see that maximum engineering accessories or devices will follow the concept of open system.

#### Closed system

In case of closed system in thermodynamics, there will not be any transfer of mass across the system boundary. However energy may transfer across the system boundary. Therefore close system in thermodynamics could be considered as fixed mass system also.

We will see the Carnot cycle and in our upcoming posts.

Do you have suggestions? Please write in comment box

#### Reference:

Engineering thermodynamics by P.K. Nag
Engineering thermodynamics by R. K. Rajput