Hydraulic diameter

For the flow in a gap with the width s between two concentric pipes with diameters D and d, there is therefore:

The hydraulic diameter is used, inter alia, for the calculation of pressure loss in non-circular cross-sections. Another field of application is in the emission measurement technique to assess the quality of the incoming flow of a test section. In general, the flow conditions are sufficiently good if the inlet pipe at least 5 hydraulic diameter and the undisturbed inlet and outlet are in straight flow channels 2 hydraulic diameter after the cross -section.

Limits of applicability

For most present in the practical cases, with the help of the hydraulic diameter, the actually prevailing flow conditions with useful accuracy determined. It can, however, relevant deviations arise when the shape of the cross section is highly irregular, or the cross section is very small, so that there Laminar flow prevails. To this end, here are two examples:

• Shape of the cross section considered:

• Laminar flow:

Hydraulic radius

The hydraulic radius is the ratio of the flow cross section A (or S) and the wetted perimeter P ( U or O):

Especially in the case of open flume is more convenient as applicable.

• Hydraulic