# Velocity Head

## Dynamic pressure and velocity head

The dynamic pressure in a fluid flow can be expressed as

pd = ρf v/ 2                                        (1)

where

pd = dynamic pressure in fluid (Pa, psf (lb/ft2))

ρf = density of fluid (kg/m3, lb/ft3)

v = fluid velocity (m/s, ft/s)

• 1 Pa = 10-6 N/mm2 = 10-5 bar = 0.1020 kp/m2 = 1.02x10-4 m H2O = 9.869x10-6 atm = 1.45x10-4 psi (lbf/in2)
• 1 psf (lbf/ft2) = 47.88 N/m2 (Pa) = 0.006944 lbf/in2 (psi)

Head water column can be calculated by dividing dynamic pressure with specific weight of water like

hw = pγw

= f v2/2) /  ρw g

= v2/ 2 g                                             (2)

where

hw = head water (m Water, ft Water)

γw  = ρw g = specific weight water (N/m3, lb/ft3)

where

ρw = density of water (kg/m3, lb/ft3)

g = acceleration of gravity (32.174 ft/s2, 9.81 m/s2)

### Air Flow - Velocity and Dynamic Head Chart

Charts are based on air density 1.205 kg/m3 and water density 1000 kg/m3.

### Velocity Heads

Velocity
- v -
(ft/sec)
Velocity Head
- v2/2g -
(ft Water)
0.5 0.004
1.0 0.016
1.5 0035
2.0 0.062
2.5 0.097
3.0 0.140
3.5 0.190
4.0 0.248
4.5 0.314
5.0 0.389
5.5 0.470
6.0 0.560
6.5 0.657
7.0 0.762
7.5 0.875
8.0 0.995
8.5 1.123
9.0 1.259
9.5 1.403
10.0 1.555
11.0 1.881
12.0 2.239
13.0 2.627
14.0 3.047
15.0 3.498
16.0 3.980
17.0 4.493
18.0 5.037
19.0 5.613
20.0 6.219
21.0 6.856
22.0 7.525
• 1 ft (foot) = 0.3048 m = 12 inches = 0.3333 yd

## Related Topics

• Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time

## Tag Search

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