How to directly measure the mean flow velocity in square cross-section pipes

The main purpose of the paper is to provide a simplified measuring procedure for evaluating the fluid flow rate in square cross section pipes. This procedure consists in directly measuring the flow (mean) velocity at a fixed location in the section. To this aim, an extension of the methodology utilized for circular section pipes is here proposed. The method simplifies and improves the procedure suggested by the technical standard EN 12599. It has been possible to locate a specific position in the cross section where to measure the mean flow velocity in order to evaluate the flow rate. Here, it is shown that the proposed methodology allows the estimation of the flow rate with higher accuracy than the normed one does, estimating errors less than those accepted in common practice. The effectiveness of the proposed method has been proved by means of a series of experimental tests performed in a wind tunnel, using a Laser Doppler Anemometer (LDA) in order to measure the punctual velocities in the test cross-section of the tunnel in order to reconstruct the velocity profiles useful to determine the fluid flow rate.