DE

FIN

ITIO

N

PR

ES

SU

RE

DR

OP

Pressure Drop - Definition

0

50

100

150

200

250

0,8 3,2 7,2 12,8 20 28,8 39,2 51,2 64,8 80

[m ³]

[m bar]

0

20

40

60

80

100

120

140

160

0,8 3,2 7,2 12,8 20 28,8 39,2 51,2 64,8 80

[m ³]

[mb ar]

DE

FIN

ITIO

N

PR

ES

SU

RE

DR

OP

Pressure Drop - Definition

General

The pressure drop constitutes the pressure differential generated between two defined points through wall friction and internal friction in static mixers, pipes, moulded parts, fittings, etc. With static mixers, these points are the intake and outlet of the mixer. In engineering, a coefficient of flow resistance ζ is used for elements installed in a pipe (mixing elements, valves, baffles, etc.), which can be taken from tables.

The pressure drop due to wall friction is determined by the coefficient of pipe friction λ. The coefficient of pipe friction depends on the Reynolds' number in the case of laminar flow. The surface roughness plays a role especially with turbulent flows.

The Theory

The equation for pressure drops in pipes with flows with the prerequisite of a constant density is:

This is the Bernoulli's energy equation, whereby the term of the static height is not taken into account because it does not represent a pressure drop.

Bases of calculation

ρ density in kg/m3

u mean flow velocity in m/s

λ Coefficient of pipe friction

l Length of the pipe in m

d Diameter of the pipe in m

ζ Coefficient of friction