The Deborah number ( symbol: ) is a dimensionless parameter of the rheology. It describes the time dependence of viscoelastic behavior of a fluid as a ratio of its relaxation time of observation:
The relaxation time would be in the simplest case, that of a Maxwell model of the fluid. As an " observation period ", for example, the inverse of the shear rate or the frequency of a mechanical excitation are understood. The smaller the Deborah number, the more fluid the fluid appears.
The inventor of the Deborah number, the Israeli Rheologe Markus Reiner, referring to the wording on a passage from the Song of Deborah: The mountains quaked before the LORD, that Sinai from before the LORD, the God of Israel. (Ri 5.5 EU) Accordingly, the mountains in the face of God in motion while they appear human observers as proof.