# the difference between concentration change due to external flow and concentration change due to int

The animated demo for the Continuity Equation with a Sink Term effectively demonstrates the conservation law's dependence on two distinct effects: convective transport and internal generation/destruction. The simulation shows the concentration ( $$n$$ ) of particles decreasing much faster than in a flow-only scenario because the positive divergence ( $$\nabla \cdot J$$, the spreading due to outward flow) works in tandem with the uniform, internal sink term ( $$-R$$, or evaporation). This principle highlights that when modeling real-world transport phenomena, any change in local concentration must be mathematically accounted for by balancing the movement of the material across boundaries ( $$\nabla \cdot J$$ ) with the rate at which the material is created or destroyed inside the volume ( $$S$$ ).

#### Narrated Video

{% embed url="<https://youtu.be/aAivSKDcTdk>" %}

#### Condensed Notes

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