A non-dimensional method to increase the accuracy of turbine flowmeters

Abstract

Abstract

Turbine flowmeters are inherently non-linear at low flowrates. A computer can, however, correct this non-linearity. The most common method of linearization currently used is based on a graph of the K factor (transducer pulses per litre) against the flowrate. This method is only accurate for the fluid properties for which the meter was calibrated. The accuracy deteriorates substantially if oil of a different viscosity, or the same oil at a different temperature, is used. This paper reports a new method of compensating for changes in viscosity over a large range.

Tests on three sizes of flowmeter were carried out, using oil and water. Two dimensionless groups, modifications of the well-known Strouhal and Reynolds numbers, were used to produce plots of the data. The results were shown to compensate for changes in viscosity and also removed some of the underlying dimensional differences between the different turbines. The resulting sixth-order polynomial is used for flowmeters of different sizes, but with a different set of coefficients for each. The final result provides both a more versatile and a more portable method of linearizing turbine flowmeters.