THEORETICAL UNCERTAINTY OF ORIFICE FLOW （孔板流量的理论的不确定性）.pdf

THEORETICAL UNCERTAINTY OF ORIFICE FLOW MEASUREMENT DANIEL MEASUREMENT AND CONTROL WHITE PAPERS page 1 THEORETICAL UNCERTAINTY OF ORIFICE FLOW MEASUREMENT INTRODUCTION Orifice meters are the most common meters used for fluid Different factors under each of the above areas are discussed flow measurement, especially for measuring hydrocarbons. with precautionary measures and installation procedures to Meters are rugged, mechanically simple, and well suited for minimize or eliminate measurement uncertainty. field use under extreme weather conditions. In 1779, an Italian COEFFICIENT OF DISCHARGE physicist named Giovanni B. Venturi (1746-1822) performed the first recorded work that used orifices for the measurement of Derivation of the basic flow equation for an orifice flowmeter fluid flow. Many years of field experience with wide range of is based on physical laws. Any derivation is accurate when meter sizes, variety of fluids, and numerous investigative tests all assumptions used to develop the equation are valid. The have identified all major contributing factors of measurement basic equation, based on simplified flow and fluid properties, uncertainty of orifice flowmeters. Because of their long history of is modified to an empirical form to adjust for complex use and dominance in the fluid flow measurement, their designs, multidimensional viscous fluid-dynamic effects. In addition, for installation requirements, and equations for flow rate calculation compressible fluids, an empiri