###### E

## Euler Number

The Euler number expresses the relationship between a local pressure drop caused by a restriction and the kinetic energy per volume of the flow.

###### E

## Eckert Number

The Eckert number expresses the relationship between a flow’s kinetic energy and the boundary layer enthalpy difference.

###### D

## Drag coefficient

The drag coefficient is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment.

###### D

## Deborah number

Deborah number is the ratio of the time it takes for a material to adjust to applied stresses and the characteristic time scale of an experiment probing the response of the material.

###### D

## Dean number

Dean number is the product of the Reynolds number through a pipe of diameter and the square root of the curvature ratio.

###### D

## Damköhler number

Damköhler number is the relation of reaction timescale to the convection time scale, the volumetric flow rate through the reactor for continuous (plug flow or stirred tank) or semi-batch chemical processes. Damköhler number can be defined as: