The control volume is described along with a lot of examples, explanations, diagrams, types, characteristics.
Let’s learn Control Volume!
When we make tea, we put some water along with some ingredients in a kettle and put it in the oven.
After a couple of minutes, due to heat from the oven, water starts boiling and vapor comes out from the kettle.
This entire kettle is having a volume, in which water takes heat energy from the oven and water vapor or mass is released to the atmosphere through its neck,
This volume is simply known as Control Volume.
In thermodynamics, the control volume is a term that is related to the study of mass and energy balance for flowing systems. There are various kinds of systems we study and to know all details, the idea of the control volume is necessary.
Let’s see the definition of Control Volume!
Control Volume is defined as the ﬁxed volume over which mass can transfer in and out across its boundary. The surface which is bounded the control volume is called Control Surface.
The knowledge of the control volume concept is essential to analyze,
A sketch of a control volume along with a control surface is indicated. It is applicable for an open system only.
In case of a closed system, we all know that no mass transfer from or to the system but energy transfer can happen. Here, we say control mass instead of the control volume.
Look at this sketch, here no mass or energy flow to the system or from the system. Like, control volume, here also control surface separates control mass from the surrounding.
Based on the deformity, the control volume is classified into two categories,
Control Volume has the following characteristics:
The control volume is to chooses based on the followings,
We know that control volume means both mass and energy can transfer through the boundary. Let us take a control volume and which undergoes process 1-2,
From the definition of entropy,
i – inlet
e – exit
Hence, entropy change in a control volume = entropy transfer by heat + net entropy transfer by mass + entropy generation in the control volume
At a glance, it seems system and control volume is the same, however, there are some differences, as follows,
|Sl. No||Description||System||Control Volume|
|1||Mass & Energy Transfer||Open system is same as control volume, but in case of closed system, mass or energy is fixed||Control volume is always fixed, and mass or energy transfer happens from the system and to the system|
|2||Example||Piston cylinder arrangement||A jet engine, air compressor|
You can solve mathematical problem on it.
Let us consider, a piston and cylinder arrangement for a closed system and a flowing liquid in an open system.
Other examples are:
Explanation of a Control Volume and its use is illustrated for clearing the concept.
We use the boiler to produce steam, and heat and the mass transfer happen here. So the boiler has a control volume. Further, it transfers to the turbine for energy output. In the turbine, it will have a control volume.
Consider, a plate is fixed and a water stream is striking on it and got deflected at 90 deg. the angle on both sides.
How do we calculate,
Hence, Fx = 7500 N
Fy = 0
F = (7500, 0)
The control volume is applicable for open system and control mass is applicable for closed system only.
These control volume and control mass both are not the same, and study is essentials to solve the problem associated with thermodynamics.
Hope, the basic idea is cleared about control volume.
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