Use of momentum balance in calibrating orifices for flow of gases

Abstract

A method of determining the absolute calibration of a gas-flow orifice without the use of gas holders or any comparative device is described. The method is based on the application of the momentum balance, as well as the energy balance, to the flow of the gas. The application requires the measurement of pressures on the face of the orifice in addition to the usual pressure-drop measurements along the axis of flow. Orifice coefficients determined by the force-momentum principle are shown to agree within an average deviation of 1.4% with those determined by other standard techniques. Also the application of the force-momentum principle demonstrates clearly why orifice coefficients are much less than unity.