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Thursday, 28 July 2016

WHAT IS CONTROL VOLUME SYSTEM IN THERMODYNAMICS?

We were discussing various forms of work in thermodynamics such as displacement work or PdV work, paddle wheel work, flow work and shaft work in thermodynamics in our previous posts. We have also seen the concept of enthalpy and concept of specific heat in our previous post.

Today we will focus here over a very important topic of thermodynamics and that is control volume system. So let us see what is control volume system in the field of thermal engineering?

Control volume in thermodynamics

Control volume system is basically defined as one fixed area in space upon which the study will be focused and mass or matter will enter in to the system and will leave the system continuously. 

Control volume system will interact with its surrounding in terms of heat energy and work energy.
Control volume system
During the process of control volume system i.e. matter is coming to the system and leaving the system continuously and during this process there will be changes in the thermodynamic properties of the matter which is flowing through control volume system.

Let us consider few examples to understand the concept of control volume system in the field of thermal engineering

Air compressor is one of the best examples of the control volume system. Atmospheric air will enter the control volume at certain thermodynamic properties and will leave the control volume system at some other thermodynamic properties.

Air compressor receives energy in terms of work from surrounding in order to provide the atmospheric air with desired properties. As we know that atmospheric air enters the control volume system i.e. air compressor at lower pressure and temperature and leaves the air compressor at higher pressure. Here, work energy will be given to the system i.e. air compressor in order to increase the pressure of the atmospheric air.
Air compressor as control volume model
Similarly, turbine is also one example of control volume system. Steam or gas will enter the system i.e. turbine at higher pressure and will leave the system i.e. turbine at lower pressure and during this process control volume system will interact with surrounding by delivering the work energy to the surrounding.
Turbine as control volume model
There is one more nice example of control volume system i.e. heat exchanger, where fluid will enter and will leave the control volume system i.e. heat exchanger continuously and heat exchanger will interact with its surrounding in terms of heat energy.

We will come again with new topic i.e. "First law of thermodynamics for an open system or control volume"in our next post .

Do you have suggestions? Please write in comment box.

Reference:

Engineering thermodynamics by P. K. Nag
Basic thermodynamics by Prof. S.K. Som
Image courtesy: Google

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