Ancillary device for flow rate measurement using dye tracer technique

Dye tracer technique is a successful tool for measuring liquid flow in closed conduits and open channels. The technique is based on the continuous injection of a tracer into the flow and on the measurement of the dilution ratio. As one of the requirements, the tracer injection rate must be known and well controlled. A device was designed to obtain this control. Such device implements a volumetric flow measurement technique and provides accurate digital display readout. Experimental results indicate that the apparatus can be used to measure the injection flow rate in a range from 235 to 2000 ml min⁻¹ with a relative error smaller than 1.5% of the reading. Even with these low injection flow, the dilution method can be applied to determine the much higher flow rates typically found in domestic or industrial outfalls as well as in artificial or natural channels. This paper also presents an application of the dilution method to flow rate measurement of an industrial outfall and the uncertainty analysis associated with the obtained values. The results indicate that the main errors of discharge estimation can arise from non-steady state flow conditions, incomplete tracer mixing, uncertainty of tracer concentration and tracer injection rate measurements.