3/19/2023 0 Comments Needed ifire flow equation![]() ![]() The ratio between true flow rate and theoretical flow rate for any measured amount of differential pressure is known as the discharge coefficient of the flow-sensing element, symbolized by the variable C. Excessive turbulence caused by rough internal pipe surfaces.Thermal expansion (or contraction) of the element and piping.Uneven velocity profiles caused by irregularities in the pipe.Unstable location of vena contracta with changes in flow.Energy losses due to friction against the pipe and element surfaces.Energy losses due to turbulence and viscosity.Causes of this discrepancy include, but are not limited to: If we compare the true flow rate through a pressure-generating primary sensing element against the theoretical flow rate predicted by an idealized equation, we may notice a substantial discrepancy. It is therefore important to figure out how to coax the most accuracy from the common orifice plate in order that we may measure fluid flows both accurately and economically. In applications such as custody transfer (also called “fiscal” measurement), where the flow of fluid represents product being bought and sold, flow measurement accuracy is paramount. Orifice plates are also the easiest type of flow element to replace in the event of damage or routine servicing. Orifice plates, despite being less than perfect as flow-sensing elements, are convenient and economical to install in flanged pipes. However, in the real world we must often do the best we can with imperfect technologies. Venturi tubes are nearly ideal, since the machined contours of the tube ensure gradual changes in fluid pressure and minimize turbulence. Orifice plates are some of the worst offenders in this regard, since the fluid encounters such abrupt changes in geometry passing through the orifice. Suffice it to say, the flow formulae we have discussed ( previous topics) so far are only approximations of reality. ![]() no energy dissipated due to friction) within the moving fluid and perfect stream-line flow (i.e. When we derived a formula for predicting flow rate from pressure dropped by a orifice or venturi tube or, we had to make many assumptions, chief among them being a total lack of friction (i.e. ![]()
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