# How to calculate the vortex flow meter minimum velocity in gas, steam and liquid applications

• ## Vortex flow meter mininum velocity in normal gas, air systems

Qρ =Q0×√(ρ 0 /ρ )

Qρ : measureable lower limit under medium’s density

Q0：the lower limit

ρ 0：density reference to air ρ 0=1.205kg/m3

ρ ：density of measured medium

Remark: for lower density and high viscosity like H2, the measurable limit will be more high and vortex meter may not suitable for this case. Only when working pressure is high.

• ## Vortex flow meter mininum velocity in liquid measurement

Vortex meter the ideal model for liquid application due to no moving parts and very low pressure drop, velocity range is 0.3~7m/s. For other liquid in high need to confirm the viscosity.

DN15≤4mPas; DN25≤5mPas; DN40~DN300≤7mPas;

Unit transfer: 1 cp=1mPa·s; 100 cp=1p;

1 cst=1mPa·s /g/cm3 ; 1cst=1mm2/s

• ## Vortex flow meter mininum velocity in steam mass measurement

As a normal rule, we also use T/hr or kg/hr as the mass unit for steam measurement. Because of the temperature and pressure are different under saturated steam and superheated steam so the steam measureable range will be different.

Q=1.5Q0×=√（ρ 0/ρ ）×ρ ×10-3(t/h)

ρ ，the measured medium’s density

Q：the measured medium’s flow rate

ρ 0，Q0：the referenced air’s density（1.205kg/m3） and flow

For example: counting the flow range under DN100, pressure at 8barG

Step 1, counting the volume range under DN100, that is 100 — 1000m3/h

Step 2, check the density under pressure 8barG, is ρ=4.162kg/m3

Step3, counting the lower limit of DN100,

Q=1.5×100×√(1.205/4.162)×4.162×10-3

=0.336 (t/h)

Step 4, counting the upper limit, not large than 70m/s

Remark: if medium is superheated steam, need to confirm the temperature and pressure both and confirm the density then.