We have seen in our previous post about the first,
second and third law of thermodynamics. We have also seen the Zeroth law of thermodynamics in our previous post.
Today we will see here the basic and fundamental concepts
in thermodynamics, those are quite important for any engineering student to
understand. Thermodynamics starts with the concept of thermodynamic system.Â
We will discuss here the concept of thermodynamic system and simultaneously we will see here the various classes of thermodynamic system with the help of this post.
We will discuss here the concept of thermodynamic system and simultaneously we will see here the various classes of thermodynamic system with the help of this post.
Thermodynamic system
Thermodynamic system is basically defined as the
finite quantity of matter or prescribed region in space where thinking will be
concentrated during analyzing a problem.
Whatever thing those are outside from the system
will be termed as surrounding and system will be separated by the surrounding
with the help of a boundary which is termed as system boundary. Â System boundary might be fixed or movable.
System and surrounding together will be considered
as universe.
Classes of thermodynamic system
There are basically three classes of a thermodynamic
system as mentioned here
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.
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.
Isolated system
In case of isolated system, there will not be any
interaction in between system and it’s surrounding or we can say that there
will not be any transfer of mass or energy across the system boundary in case
of isolated system and therefore isolated system in thermodynamics could be
considered as fixed energy and fixed mass system.
Let us see one example of cooking rice in pressure cooker.
When we will go for cooking the rice in pressure
cooker, what we will do? We will use rice and water as contents for pressure
cooker and will place over the gas stove. Now, pressure cooker placed over the
gas strove here will be considered as closed system if pressure cooker lid is
perfectly closed, safety valve is also perfectly closed and whistle is in
position i.e. not blowing.
Because there will not be any transfer of mass
across the pressure cooker here, while heat energy is being provided to the
contents of pressure cooker i.e. rice and water. Therefore it could be
considered as closed system as only heat energy transfer take place across the
pressure cooker not mass.
When whistle starts blowing, at that time we will consider
the contents of pressure cooker as open system because generated steam will
leave the pressure cooker when whistle blows. Now let us think the condition here
during the blowing of cooker whistle, mass and energy both are transferring across
the pressure cooker so we may call this as open system.
If we are having one vessel which is perfectly insulated,
closed and rigid, then we may refer this as isolated system because there is no
transfer of energy or mass across the vessel.
There are few more types of systems those are quite
important to be considered here i.e. adiabatic system, homogeneous system and heterogeneous
system.
Adiabatic system
Adiabatic system will not permit the exchange of
heat energy with its surrounding, however it will permit to exchange the work
energy with its surrounding.
Homogeneous system and heterogeneous system
Homogeneous system will consist single phase such as
mixture of water vapor and air.
Heterogeneous system will consist two or more than
two phases such as steam and water
We will start our discussion with thermodynamic equilibrium, intensive and extensive properties
in
our next post.
Do you have any suggestion? Please write in comment
box.
Image courtesy:
Google
Reference:
Engineering
thermodynamics by P.K Nag
Engineering
thermodynamics by R.K Rajput
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