What Factors Should Be Considered When Choosing a Control Volume?

[member 392791]

Hello,

My professor did a lecture about mass conservation in a system. He basically explained the lining that separates the system from the surroundings is the control surface, and all that is contained within the system is the control volume.

I think it was explained rather loosely, and we need to have a firm understanding of the concept. I think it was somewhat vague as to the applications of control volumes and how to choose it for a given problem, or even what it really is. I feel somewhat lost on this part, and my textbook is not followed closely by the instructor.

I was wondering if anyone knew some good literature to read on choosing control volumes and explaining what it means, if not if someone could give some explanation, I would be very grateful.

Thank you

 

[Simon Bridge]

The point is that it does not matter how you choose the control volume - so long as the volume enclosed is isolated. It's an entirely abstract concept. If you are also doing a practical course, you will learn more about what constitutes a control there.

 

[Q_Goest]

There's some background here: https://www.physicsforums.com/library.php?do=view_item&itemid=365

 

[Chestermiller]

See Transport Phenomena by Bird, Stewart, and Lightfoot

 

[alphy]

for your question. Control volumes are an important concept in the study of fluid mechanics and thermodynamics. They allow us to analyze a system by defining a specific region where we can apply principles of mass, energy, and momentum conservation. Choosing a control volume can be a crucial step in solving a problem, as it determines what is included in the analysis and what is not.

One way to think about control volumes is to imagine a physical boundary that separates the system of interest from its surroundings. This boundary can be fixed or moving, and it can have any shape or size. The control volume is then defined as the region enclosed by this boundary. Everything within the control volume is considered part of the system, while everything outside is considered part of the surroundings.

When choosing a control volume, there are a few factors to consider. First, it should enclose all the relevant components and interactions that are important for the problem at hand. This means that any inflow or outflow of mass, energy, or momentum should be included in the control volume. Additionally, the control volume should be chosen in a way that simplifies the problem and makes it easier to apply the conservation principles. This could mean choosing a control volume that aligns with the symmetry or geometry of the system, or one that eliminates unnecessary complexities.

As for literature, there are many textbooks and online resources that discuss the concept of control volumes in more detail. Some recommended readings include "Fundamentals of Momentum, Heat, and Mass Transfer" by James Welty, "Fluid Mechanics" by Frank White, and "Thermodynamics: An Engineering Approach" by Yunus A. Cengel and Michael A. Boles. It may also be helpful to consult with your professor or classmates for further clarification on specific examples and applications. I hope this helps to clarify the concept of control volumes and its importance in analyzing systems.