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4 lis 2012 · Critical (Choked) Pressure Drop. With choked flow and critical pressure drop, the outlet pressure - p o - after the control valve is aprox. 58% of the inlet pressure - p i - before the control valve. The flow coefficient at choked - or critical - flow can be expressed as: C v = m / (1.61 p i) (2) where. m = steam flow (lb/hr)
A Cv flow coefficient specifies the amount of water at 60°F (15.55 °C) in US gpm that will flow through a valve and produce a 1.0 psi pressure drop. Thus a Cv flow coefficient of 10 indicates that a 1.0 psi pressure drop will occur with a 10 US gpm of water throughput through the valve.
Where flowing water water is exposed to the atmosphere, and thus not under pressure, its condition is called open channel flow. Typical design challenges can be: Determining how deep water will flow in a channel. Finding the bottom slope required to carry a defined flow in a channel.
For critical flow, the following formula can be used to calculate the volumetric flow through a valve of coefficient Cv : Qv=F L *Cv/1.156.√(ΔP s /d) Q v =Flow rate (m3/h) F L = critical flow factor
In fluid dynamics, the pressure coefficient is a dimensionless number which describes the relative pressures throughout a flow field. The pressure coefficient is used in aerodynamics and hydrodynamics. Every point in a fluid flow field has its own unique pressure coefficient, Cp.
Cv for liquids is the volume of 68°F water in U.S. gallons per minute that passes through a valve at a pressure drop of 1 PSI. Flow for a given Cv is typically calculated from the following formula. Where: Q = Valve flow rate in gallons per minute (US GPM) ΔP = Difference between upstream and downstream pressure in pounds per square inch (PSI)
Based on M = 0.96, the critical pressure coefficient was found to be −0.0697. A pressure coefficient below this critical pressure coefficient constitutes the supercritical region or the region of supersonic flow on the surface of the wing.
