Experimental study for the use of elbows as flowmeters

A study of fluid flow in elbows for application in flow metrology was undertaken. Most of the current flow measurement methods represent a great investment for many industries, however, when the accuracy requirements are not too high, elbows could be used as primary elements for flow rate measurements because they represent a very low cost instrument, easy to install and operate as well. The studies already made for the application of this device, indicate that more investigation is necessary for its full characterization. In the experimental work reported in this paper, three commercial 90° elbows, installed horizontally, were tested. All of them were short curvature radius with 0.75, 1 and 1.5 inches of internal diameter; water was employed for the experiments and maintained at 24 °C. Pressure taps on the elbows were located at 45° along the curvature radius, one on the internal wall and the other on the external. The performance of the elbow was compared against a calibrated orifice plate. A mathematical model based on the centrifugal force in the elbow, was developed to describe the effects of the curvature on the radial pressure gradient. Experimental results show that there is a greater sensibility of the elements when the curvature radius diminishes, that is, a larger pressure gradient is obtained. If this radial pressure gradient is used in the typical equation for the orifice plate, a good concordance between the measurements of both elements is observed and it only requires a correction factor to use the elbow as a flowmeter. We concluded that the radial pressure gradient is adequate for the flow rate determination and that it is possible to use elbows as flowmeters.