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Orifice plate showing vena contracta. An orifice plate is a thin plate with a hole in it, which is usually placed in a pipe. When a fluid (whether liquid or gaseous) passes through the orifice, its pressure builds up slightly upstream of the orifice [1] but as the fluid is forced to converge to pass through the hole, the velocity increases and the fluid pressure decreases.
The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice valve or other assembly and the corresponding flow rate. Mathematically the flow coefficient C v (or flow-capacity rating of valve) can be expressed as
In a nozzle or other constriction, the discharge coefficient (also known as coefficient of discharge or efflux coefficient) is the ratio of the actual discharge to the ideal discharge, [1] i.e., the ratio of the mass flow rate at the discharge end of the nozzle to that of an ideal nozzle which expands an identical working fluid from the same initial conditions to the same exit pressures.
All gases flow from higher pressure to lower pressure. Choked flow can occur at the change of the cross section in a de Laval nozzle or through an orifice plate. The choked velocity is observed upstream of an orifice or nozzle. The upstream volumetric flow rate is lower than the downstream condition because of the higher upstream density.
The coefficient of contraction is defined as the ratio between the area of the jet at the vena contracta and the area of the orifice. C c = Area at vena contracta/Area of orifice. The typical value may be taken as 0.611 for a sharp orifice (concentric with the flow channel). [2] [3] The smaller the value, the greater the effect the vena ...
For example, an orifice plate produces a pressure drop that is a function of the square of the volume rate of flow through the orifice. A vortex meter primary flow element produces a series of oscillations of pressure. Generally, the physical property generated by the primary flow element is more convenient to measure than the flow itself.
A restrictive flow orifice (RFO) is a type of orifice plate.They are used to limit the potential danger, damage, or wastage of an uncontrolled flow from, for example, a compressed gas cylinder [1] [2] They are generally not limiting the flow during normal operation but if a fault or failure occurs causing uncontrolled flow the orifice will present a restriction, limiting the flow.
The Hazen–Williams equation is an empirical relationship that relates the flow of water in a pipe with the physical properties of the pipe and the pressure drop caused by friction. It is used in the design of water pipe systems [ 1 ] such as fire sprinkler systems , [ 2 ] water supply networks , and irrigation systems.