Pressure Losses

Application examples

SAFI DN 1200 ventilation damper pressure loss ratio equals to K = 7,3 when the ventilation damper is open at 45°

Question : follow the pressure loss ∆P according to the volume flow rate Q for an air at 20°C and at ambient pressure.
Answer :
We use the formula presented in the paragraph ‎3.1, then :

 (1)

where

1. K = 7,3
2. m is the air density at T = 20°V and P = 1013,23 hPa = 101325 Pa
3. VS is the air speed in m/s in the section S = π.(0,6)2

We shall remember the link between the volume flow rate and the fluid speed, then:

Where

1. Q is the volume flow rate in m3/s
2. VS is the average fluid speed in m/s
3. S is the damper section in m2, that is to say S = 1,13 m2

We can then rewrite the equation (1) :

 (2)

In order to calculate the air density in specified temperature and pressure conditions, it is essential to recall the law of pure gas and its corollary giving the density:

Where

1. P is the fluid absolute pressure in Pa.
2. M is the considered fluid molar mass (for air M = 28,96.10-3kg)
3. R is the pure gas constant. R = 8,317 in J/(K.mole)
4. T is the fluid temperature in Kelvin (T in K = T in °C + 273,15)

For our application, we find :kg/m3

In the equation (2), by replacing all the parameters by their numerical values, we therefore find :

We obtain the following curb :

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