What is Thermodynamic Equilibrium State of Engineering Systems?

In engineering, there are various kinds of disciplines and one of these disciplines is thermodynamics. Thermodynamics is a very useful tool to see the general state of the system on hand. The general assumptions and approximations can be made with thermodynamical analyses of a system. For example, the theoretical efficiency of an internal combustion engine can be calculated with thermodynamical analyses and calculation of each equilibrium state of each cycle. Total energy production and consumption can be calculated. 

Here, the equilibrium state is a very important factor and it must be well understood by the person who is making thermodynamical calculations. You can find a good definition of thermodynamical equilibrium in this article. 

What is Equilibrium State in Thermodynamics? 

Explanation of a thermodynamical system.

In engineering, there are variıus moving and active machineries such as refrigerators and engines. To make healthy calculations about them, we would like to see the equilibrium state of these active systems. The meaning of these states that there are no unclean parameters to calculate other thermodynamical parameters. So, there must be some equilibrium states that must be satisfied to find the clean thermodynamical state to make calculations.  

Mechanical Equilibrium

The first and the most important equilibrium state condition is the mechanical equilibrium. In the mechanical equilibrium of a system, there are no forces, pressure, or other mechanical driving factor to make the activity or move to change the mechanical situation of the system. 

In general, the gravitational force is neglected as a driving mechanical factor. 

Thermal Equilibrium

In thermal equilibrium, there is no heat transfer, heat flux, or flow between surroundings and the system on hand. So, we know the total heat and heat energy of the system to make our calculations. Otherwise, the system will be thermally active which can not be stated as thermal equilibrium. 

Phase Equilibrium

Balance is important for each equilibrium states.

The third equilibrium condition of the thermodynamic equilibrium state is the phase equilibrium. Systems consist of different phases such as liquid casting metals.  If two or more phases are in balance in terms of masses, phase equilibrium is provided. Phase equilibrium is dependent on the chemical equilibrium. 

Chemical Equilibrium

If there are no chemical reactions in a thermodynamical system on the hand, chemical equilibrium is provided. There can be chemical reactions between different phases. But if there are no chemical reactions and balance is maintained, chemical equilibrium is obtained. 

So, each of these equilibrium states must be satisfied to obtain a thermodynamical equilibrium state to make thermodynamical calculations. 


The thermodynamical state and equilibrium can be summarized like above from an engineering viewpoint. 

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