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Velocity Head

Dynamic pressure and velocity head

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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.

Air Flow - Velocity and Head

Water Flow - Velocity and Dynamic Head Chart

Air Flow - Velocity and Head

 

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
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Tag Search

  • en: velocity head major pressure loss
  • es: pérdida importante de presión cabeza de velocidad
  • de: Geschwindigkeitshöhe großen Druckverlust
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