Flow MeasurementFlow Measurement(variable head meter)(variable head meter)

bybyAshfaq Md. AnseryAshfaq Md. Ansery

Venturimeter

Venturimeter

Theory (Venturimeter)

Discharge Coefficient Cd

Dimensional analysis of venturi tube indicates C = f (Re, D1, D2)

Discharge Coefficient

Venturimeter cont…. The value of C

C = 0.99 for large tube C= 0.97-0.98 for small tube

Provided the value is such as to give reasonably high Reynolds number

A roughing of the surface of the converging section from age or scale deposit will reduce the coefficient slightly (1-2%)

Venturimeter cont…Limitations High installation cost It occupies considerable

space

Limitations (cont…) Ratio of throat to pipe diameter

(D2/D1) cannot be changed- the maximum measurable flow rate is fixed

So if the flow range is changed, the throat diameter may be too large to give an accurate reading or to small to accommodate the next maximum flow rate