Question

Why coefficient of discharge is less than expected value for the rectangular notch?

Answer 1

Venturimeter is the best and most efficient primary transducer for measuring flow rate and produces almost no pressure losses and loading effect while measurements.

But practically speaking, while measuring flow some losses do occur and are almost un-avoidable like frictional losses, pressure losses, turbulence losses etc. Generally Coefficient of discharge of venturimeter is 0.95 to 0.97 which is highest of all flow measuring primary transducer’s. Only 10% of pressure losses are seen in venturimeter while measurement.