Effects of cavitation and plate thickness on small diameter ratio orifice meters

High differential pressure drop is frequently required in the process line of electric power plants. However, cavitation produced by a high pressure drop could damage the pipe and pump blades. In these experiments, the effects of cavitation and plate thickness for small-bore diameter (d) to pipe diameter (D) ratio (β = d/D) orifice plates were evaluated in a 100 mm diameter test section of a water flow calibration facility. Three size orifice meters were tested with β = 0.10, 0.15, and 0.33 and no bevel on the throat. The cavitation number at inception was measured to be 1.0 to 1.2 for all experiments. Although cavitation occurred in all experiments, the discharge coefficient was affected by cavitation only for the smallest bore (β = 0.10) and thickest plate tested, 7.0 mm or t/d = 0.70 where t is the plate thickness. Thickness seemed to influence the discharge coefficient only for the β = 0.10 plate. But the trends in the results for thickness were not conclusive and could be attributed to edge sharpness.