The direction of flux vectors in derivation of conservation of mass

In summary, the conservation law of mass states that the net mass entering a control volume must be equal to any variation of mass within the control volume during a given time interval. This applies to control volumes of any size and can change during the time interval.
  • #1
Mart1234
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In the derivation of the conservation law of the conservation of mass, the flux on one side enters and the flux on the other side leaves the control volume. I presume this is due to the assumption that the volume is infinitesimally small and hence v(x,y,z,t) will not change directions dramatically within the control volume. Is this the correct way of thinking about this or am I missing something?
 
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  • #2
:welcome:

That sounds plausible, but without the context it's difficult to say.
 
  • #3
No, what the law of conservation of mass says is that, during a given time interval, any variation of mass inside a control volume must be equal to the net mass that traverses the control surface during that same time interval. Not only the control volume can be of any size, but it can also increase or decrease during that time interval.
 

FAQ: The direction of flux vectors in derivation of conservation of mass

What is the significance of the direction of flux vectors in the derivation of conservation of mass?

The direction of flux vectors is crucial because it indicates the flow of mass through a control surface. In the context of the conservation of mass, these vectors help in quantifying the rate at which mass enters or leaves a given volume, ensuring that the mass balance is accurately described.

How do flux vectors relate to the continuity equation in fluid dynamics?

Flux vectors are directly related to the continuity equation, which is a mathematical expression of the conservation of mass. The continuity equation states that the rate of change of mass within a control volume equals the net flux of mass across its boundaries. The direction and magnitude of flux vectors help determine this net flux.

Why is it important to consider the direction of flux vectors when applying Gauss's theorem?

Gauss's theorem, or the divergence theorem, relates the flux of a vector field through a surface to the divergence of the field within the volume enclosed by the surface. Considering the direction of flux vectors ensures that the correct sign and magnitude are used when integrating over the surface, which is essential for accurately applying the theorem to derive conservation laws.

Can the direction of flux vectors affect the interpretation of boundary conditions in a conservation of mass problem?

Yes, the direction of flux vectors can significantly affect the interpretation of boundary conditions. For example, specifying whether mass is entering or leaving a boundary is dependent on the direction of the flux vector at that boundary. Incorrectly accounting for this direction can lead to errors in the formulation and solution of the problem.

How do you determine the direction of flux vectors in a given physical system?

The direction of flux vectors is typically determined by the physical properties of the system, such as the velocity field in fluid dynamics. For instance, in a fluid flow, the flux vector direction is aligned with the velocity vector of the fluid particles. Analytical methods, computational simulations, or experimental measurements can be used to ascertain these directions.

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