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 , and nonnegative 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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