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A simplified version of the definition is: The k v factor of a valve indicates "The water flow in m 3 /h, at a pressure drop across the valve of 1 kgf/cm 2 when the valve is completely open. The complete definition also says that the flow medium must have a density of 1000 kg/m 3 and a kinematic viscosity of 10 −6 m 2 /s, e.g. water. [clarify]
Pressure drop (often abbreviated as "dP" or "ΔP") [1] is defined as the difference in total pressure between two points of a fluid carrying network. A pressure drop occurs when frictional forces, caused by the resistance to flow, act on a fluid as it flows through a conduit (such as a channel, pipe , or tube ).
In thermodynamics, the Joule–Thomson effect (also known as the Joule–Kelvin effect or Kelvin–Joule effect) describes the temperature change of a real gas or liquid (as differentiated from an ideal gas) when it is expanding; typically caused by the pressure loss from flow through a valve or porous plug while keeping it insulated so that no heat is exchanged with the environment.
pressure drop across constriction (unit force per unit area) The above equations calculate the steady state mass flow rate for the pressure and temperature existing in the upstream pressure source. If the gas is being released from a closed high-pressure vessel, the above steady state equations may be used to approximate the initial mass flow rate.
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.
This type of pressure measurement may be more convenient, for example, to measure fuel or combustion pressures in jet or rocket engines. The first large-scale Venturi meters to measure liquid flows were developed by Clemens Herschel who used them to measure small and large flows of water and wastewater beginning at the end of the 19th century. [3]
Differential pressure sensors are used to measure many properties, such as pressure drops across oil filters or air filters, fluid levels (by comparing the pressure above and below the liquid) or flow rates (by measuring the change in pressure across a restriction). Technically speaking, most pressure sensors are really differential pressure ...
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.