Study on discharge coefficient of perforated orifices as a new kind of flowmeter

Abstract

A perforated orifice is promising in measuring flowrates accurately as a differential pressure device. In this study, the discharge coefficient of a perforated orifice, characterizing the relationship between the volumetric flowrate and the pressure drop across the orifice is presented. Different structures are tested experimentally including orifice thickness, porosity, hole distribution and upstream disturbance. For each case, a wide range of flowrate was tested in a horizontal single-phase water pipe with an I.D. of 29mm. For comparison, the discharge coefficient was also obtained for the corresponding standard orifice with the same porosity and thickness. Meanwhile, the effect on the discharge coefficients of the structural parameters was assessed in terms of pressure drop. The theoretical analysis shows that a perforated orifice yields a weaker distortion to the flow than the corresponding standard orifice, indicating a lower pressure drop and a more stable flow field for the former. The experimental results show that the discharge coefficient of a perforated orifice is 22.5–25.6% larger but with a weaker scattering than that of the corresponding standard orifice. Furthermore, a perforated orifice has a lower critical Reynolds number and a stronger anti-disturbance ability. As a flowmeter, the perforated orifice is comparable to the newly developed differential pressure orifices, e.g. V-cone and slotted orifices, but with a simpler structure.