= Volume viscosity
{title2=$\zeta_B$}
{wiki}
= Bulk viscosity
{synonym}
Bulk viscosity is the dissipative response to a fluid's volume expansion or compression, distinct from the shear response. For a Newtonian isotropic fluid its isotropic dissipative stress includes $\zeta_B(\nabla\cdot\mathbf v)I$, and nonnegative $\zeta_B$ gives nonnegative compression-related dissipation. A condensate's relative-density-flow bulk coefficient must be identified from its particular hydrodynamic equation; it is not automatically numerically identical to a dimensional Newtonian viscosity.
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