# 5.3.1: Non Deformable Control Volume

When the control volume is fixed with time, the derivative in equation (??) can enter the integral since the boundaries are fixed in time and hence,

Continuity with Fixed b.c.

\[

\label{mass:eq:intSrho}

\int_{V_{c.v.}} \dfrac{d\,\rho}{dt} dV = -\int_{S_{c.v.}} \rho\,U_{rn} \, dA \tag{12}

\]

Equation (??) is simpler than equation (??).

### Contributors

Dr. Genick Bar-Meir. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or later or Potto license.