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I have seen the expression for mass flow rate in one of the problems I am working on. I used to simply apply the expression for calculating the mass flow rate with respect to the position as (ρu + (∂u ∕∂x)dx) dy dz). ρ, u are density and velocity component respectively.

I would like to understand the exact meaning of multiplication of (∂u ∕∂x)dx.

I expect a good explanation as soon as possible.

Thanks in advance.

Madguy

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# Meaning of a PDE expression

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