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terminology problem 1
- Thread starter m777182
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In the Bernoulli equation for incompressible fluids flowing between points 1 and 2:
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 [ρ]g 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, [Δ]Pf/[ρ]g.
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.
[Δ]Pf 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 [ρ]V2/2 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.
p1/[ρ]g + V12/2g + z1 = p2/[ρ]g + V22/2g + z2
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 [ρ]g 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, [Δ]Pf/[ρ]g.
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
[Δ]Pf prop. to (L/D)([ρ]V2/2)
I omitted the demonstration of this formula for the sake of simplicity.
[Δ]Pf 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 [ρ]V2/2 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.
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