We will calculate the following items:
1. Minimum measurable flow rate
2. Maximum measurable flow rate
3. Accuracy after temperature and pressure correction (examples: for 100 and
150 m
3
/h (normal))
1. Minimum measurable flow rate (volumetric flow rate (m
3
/h) and mass flow rate (m
3
/h (normal))
First, the minimum measurable velocity is determined as the larger of 0.3 m/s or
the velocity at Re 3500. The velocity at Re 3500 is calculated from the formula for
calculating Re:
V = Re × ν/D.
Here, if Re = 3500, ν = 1.883 × 10
–6
m
2
/s, and D = 78 × 10
–3
m,
V = 3500 × 1.883 × 10
–6
/(78 × 10
–3
) = 0.08 m/s.
Since a velocity of 0.08 m/s at Re 3500 is less than 0.3 m/s, the minimum measur-
able velocity is 0.3 m/s.
Now, the minimum measurable volumetric flow rate can be calculated as
Qactual (m
3
/h) = S × V × 3600 = 5.2.
S: flow path cross-section of
MVF080
(m
2
) = (78 × 10
–3
)
2
× π/4
V: velocity (m/s) = 0.3
Therefore, volumetric flow rate can be measured down to 5.2 m
3
/h.
Next, we can calculate the minimum mass flow rate Qnormal (m
3
/h (normal)) at
0 °C and pressure of 101.3 kPa, with temperature and pressure correction.
Qnormal (m
3
/h(normal)) = 5.2 × ((273+0)/(273+23)) × ((101.3+700)/101.3)= 38
Amount of tempera-
ture correction
Amount of pressure
correction
Therefore, mass flow rate can be measured starting from a minimum of 38 m
3
/h
(normal).
2. Maximum measurable flow rate (volumetric flow rate (m
3
/h) and mass flow rate (m
3
/h (normal))
MVF
flowmeters can measure velocity up to 30 m/s.
The volumetric flow rate Qactual (m
3
/h) at velocity 30 m/s is determined by
Qactual (m
3
/h) = S × V × 3600 = 516.
S: flow path cross-section of
MVF080
(m
2
) = (78 × 10
–3
)
2
× π/4
V: velocity (m/s) = 30
The volumetric flow rate can be measured up to 516 m
3
/h.
Next, we can calculate the mass flow rate at 0 °C and pressure of 101.3 kPa, with
temperature and pressure correction, by
Qnormal (m
3
/h(normal)) = 516 ×((273+0)/(273+23)) × ((101.3+700)/101.3)= 3765
Amount of tempera-
ture correction
Amount of pressure
correction
Mass flow rate can be measured up to 3765 m
3
/h (normal).
20
Chapter 5. SPECIFICATIONS
