Home> FAQ

FAQ

Air flow calculation

Air flow(Q):(a.k.a. volume flow rate) the flow rate through the Cross-sectional area of pipe, the formula is:
Q=60VA
Q (Air flow)=m3/min
V (Air velocity)=m/sec
A (Cross-sectional area)=m2


Common Conversion formula for pressure

1Pa=0.102mmAq
1mbar=10.197mmAq
1mmHg=13.6mmAq
1psi=703mmAq
1Torr=133.3pa
1Torr=13.3 mmAq
1Torr=1.333mbar


Common Conversion formula for air flow

1m3/min(CMM)=1000 l/min = 35.31 ft3/min(CFM)


Common Terms explanation

(1) Standard temperature and pressure: for
short "STP", in a condition of 20 degrees Celsius, 760mmHg absolute pressure, and 65% Relative
Humidity. The weight for 1m3 of air is 1.2kg in this condition.
(2) Absolute pressure of air: the sum of atmospheric pressure plus Gauge pressure. Usually expressed in units with kgf/m2 or mmaq.
(3) Normal temperature and pressure: for short "NTP", in a condition of 0 degrees Celsius, 760mmHg absolute pressure, and 0% Relative Humidity. The weight for 1m3 of air is 1.293kg in this condition.


Pressure

(1) Static pressure(Ps): The pressure of a fluid exerts on a surface at rest. It is resulted by gravity and impeller in blower and fan, which can be measured directly. Usually expressed in units with kgf/m2 or mmaq.
(2) Velocity pressure(Pv): (a.k.a. Dynamic Pressure) The pressure of a fluid in motion. Usually expressed in units with kgf/m2 or mmaq.
(3) total pressure: The sum of Static pressure plus Velocity pressure. Usually expressed in units with kgf/m2 or mmaq. The total pressure is a fixed value for blower and fan, it is not changed when reducing the diameter of pipe.


Air pressure and temperature

Density of air changes with variances in temperature. If other conditions are fixed, the air pressure has to be adjusted by the following formula when variances in temperature:
P= P'(273+t/293) (mmAq)
Same reason, when variances in density of air:
P=P'(1.2/γ) (mmAq)
The P', t, andγare measured pressure, temperature, and density of air.


Air pressure and velocity

Pressure is proportional to the velocity.
Pv=γ×(V2 / 2g)
Pv: Velocity pressure(mmAq)
γ: proportion of air(kg/m3)
g: Acceleration of gravity(m/s2)=9.8
V: velocity(m/s)