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to arrive at:

LaTeX Math Block
anchorS8TNBpre_filnal
alignmentleft
\rho \, \phi \, c_t  \cdot \frac{\partial p}{\partial t} + \nabla \, ( \rho \, {\bf u}) = \rho \, \sum_k q_k(t) \cdot \delta({\bf r}-{\bf r}_k)
LaTeX Math Block
anchorqk
alignmentleft
\int_{\Sigma_k} \, {\bf u} \,  d {\bf A} = q_k(t)

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Then use the following equality:

LaTeX Math Block
anchor1nabla_rho
alignmentleft
\nabla \, ( \rho \, {\bf u}) =  \rho \, \nabla \, {\bf u} + (\nabla  \rho, \, {\bf u}) =  \rho \, \nabla \, {\bf u} + \frac{d\rho}{dp} \cdot (\nabla  p, \, {\bf u}) = \rho \, \nabla \, {\bf u} + \rho \, c \cdot (\nabla  p, \, {\bf u})

where 

LaTeX Math Inline
body--uriencoded--\displaystyle c(p) = \frac%7B1%7D%7B\rho%7D \frac%7Bd\rho%7D%7Bdp%7D
 is fluid compressibility.


Substituting

LaTeX Math Block Reference
anchornabla_rho
 into
LaTeX Math Block Reference
anchorpre_filnal
 and reducing the density 
LaTeX Math Inline
body\rho(p)
 one arrives to:

LaTeX Math Block
anchorpre_filnal
alignmentleft
\rho \, \phi \, c_t  \cdot \frac{\partial p}{\partial t} + \nabla \, ( \rho \, {\bf u}) = \rho \, \sum_k q_k(t) \cdot \delta({\bf r}-{\bf r}_k)
LaTeX Math Block
anchorqk
alignmentleft
\int_{\Sigma_k} \, {\bf u} \,  d {\bf A} = q_k(t)


See also

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Physics / Mechanics / Continuum mechanics / Fluid Mechanics / Fluid Dynamics / Pressure Diffusion / Pressure Diffusion @model / Single-phase pressure diffusion @model

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