Sunday, 19 June 2016



We were discussing “Thermodynamics system, boundary and surrounding” in our previous post. We have also seen the thermodynamic properties and thermodynamics equilibrium in our previous post. Let us start one more discussion about very interesting subject i.e. Thermal engineering.

Today we will look here the thermodynamic state, process and thermodynamic cycle with the help of this post.

So let us see first here thermodynamic state.

Thermodynamic state is basically defined as the condition of the system at any given point of time as measured by the values of its properties. We can also express the thermodynamic state as each unique condition of a thermodynamic system will be termed as thermodynamic state. State of a thermodynamic system will provide the complete information about the system.

An operation will be termed as change of state if changing takes place in one or more than one properties of the system. Let us see one example, let we have water 250 ml at a temperature of 30 degree Celsius in a pan and this is the state of the system. Now if we are changing one property say it temperature, let we have heated the water to raise the temperature up to 80 degree Celsius now state of system changed as we have changed the value of one property here i.e. temperature

Let us see the thermodynamic process

When a thermodynamic system passes through a change in state, succession of states passed will be termed as path of the system or path of change of state. If path of change of state is completely specified, path of change of state will be termed as thermodynamic process. In simple way we can say that thermodynamic process will occur, if a thermodynamic system is undergoing through a series of change of states.

During a thermodynamic process, there will be change in one property of the system or more than one property of the system or also possible that there will be change in all of the properties of the system.

There are so many thermodynamic processes such as

  1. Isothermal process
  2. Isochoric process
  3. Adiabatic process
  4. Isobaric process
  5. Isentropic process
  6. Isenthalpic process
  7. Reversible process
  8. Irreversible process
We will discuss each and every thermodynamic process in detail in our next post.

Let us see the thermodynamic cycle

Any thermodynamic process or series of processes will be termed as thermodynamic cycle, when thermodynamic system undergoes through such changes of states that initial state is similar with final state.

Following figure indicates the thermodynamic cycle drawn between Pressure and volume. System starts with condition 1 and reaches at condition 2 by following constant pressure process. Again system reaches condition 3 by following constant volume process and finally reaches to initial condition 1. So we may see here that final condition and initial condition of the system are similar even system has completed processes 1 to 2 and 2 to 3 and finally 3 to 1.
Thermodynamic cycle

We will discuss “Quasi static or quasi equilibrium process” in our next post.

Image courtesy: Google
Do you have any suggestions? Please write in comment box
Reference: Engineering thermodynamics by P.K. Nag

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