Selection of measuring slots for slotted flowmeters

Conclusions

The selection of the type of measuring slot for flowmeters is determined by the operating conditions.

Any type of slot can be used for measuring at a constant density. However, it is advisable to use a rectangular slot which is simpler to manufacture. The selection of measuring units (in terms of a volumetric or mass flow) in this instance is immaterial, since volumetric flow is easily convertible to mass flow and vice versa.

A rectangular slot should also be used when the liquid density deviates by ±(2–2.5) from its mean value. The instrument should then be calibrated in units of mass flow.

For considerable variations of density (δρ±2.5%), for instance, produced by changes in the liquid composition and temperature or by variations in the number of gas bubbles in the liquid, it is advisable to use a proportional measuring slot. The instrument in this case should be calibrated in units of mass flow.