terminology problem
terminology problem
(OP)
I came across a term "number of inlet velocity heads", it has to do with a pressure drop and I do not quite understand it. Can somebody please explain the meaning of it to me?
m777182
m777182





RE: terminology problem
the first term is called pressure head, and the second term is called velocity head, and is measured in dimensions of height or length. Multiplying it by ρg one gets the dimensions of force per unit area, N/m2, ie, pressure.
The above-given energy balance formula has to be modified for real fluids by adding to the right side a loss of mechanical energy converted to heat due to friction, ΔPf/ρg.
In an horizontal circular conduit (z1=z2) of constant diameter D, the pressure drop between two points separated by a distance L, at constant rate of flow, is totally due to friction, namely
I omitted the demonstration of this formula for the sake of simplicity.
ΔPf in pipe fittings is usually given either as the equivalent length of straight pipe, Le, which gives the same pressure drop as the fitting in question, or as a factor, n (number of velocity heads) by which ρV2/2 has to be multiplied to give the pressure drop.
The friction drop due to contractions or enlargements, as for inlets to vessels, are also expressed in this way.