Dynamic Pressure
Dynamic pressure is the kinetic energy of a flowing fluid - liquid or gas - per unit volume - and can be expressed as
p d = 1/2 ρ v 2 (1)
where
p d = dynamic pressure (N/m 2 (Pa), lb f /ft 2 (psf))
ρ = density of fluid (kg/m 3 , slugs /ft 3 )
v = velocity (m/s, ft/s)
Dynamic Pressure Calculator - SI Units
The default values below are for water with density of 1000 kg/m 3 .
- 1 N/m 2 = 1 Pa = 1.4504x10 -4 lb f /in 2 (psi) = 0.02089 lb f /ft 2 (psf) = 1x10 -5 bar = 4.03x10 -3 in water = 0.336x10 -3 ft water = 0.1024 mm water = 0.295x10 -3 in mercury = 7.55x10 -3 mm mercury = 0.1024 kp/m 2 = 0.993x10 -5 atm
Dynamic Pressure Calculator - Imperial Units
The default values below are for water with density of 1.940 slugs .
Some common densities at atmospheric pressure:
- Water - 0 o C - 1000 kg/m 3
- Water - 32 o F - 1.940 slugs/ft 3
- Air - 20 o C - 1.2 kg/m 3
- Air - 60 o F - 2.373 10 -3 slugs/ft 3
Example - The Dynamic Pressure in a Water Flow
The dynamic pressure in water with - temperature 20 o C - density 1000 kg/m 3 and velocity 5 m/s - can be calculated as
p d = 1/2 (1000 kg/m 3 ) (5 m/s) 2
= 12500 Pa
= 12.5 kPa
Example - Hurricane and Force acting on a Wall
The dynamic pressure in a hurricane with air temperature 20 o C, density of air 1.2 kg/m 3 and wind speed 37 m/s can be calculated as
p d = 1/2 (1.2 kg/m 3 ) (37 m/s) 2
= 821 Pa (N/m 2 )
The force acting directly on a wall with area 10 m 2 can be calculated as
F = p d A
= (821 N/m 2 ) (10 m 2 )
= 8210 N
= 8.2 kN
- almost the weight of a small car.
Note! - the real force acting on the wall - or an other obstruction in the wind - is in general more complicated to calculate due to drag , turbulence and other effects.
Related Topics
• Fluid Mechanics
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
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