How to determine the lower limit of vortex flow meters in gas, steam and liquid application

Normal gas:

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 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


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,


=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.