Minimum Submergence and Froude Number
Minimum Submergence and Froude Number
(OP)
Hi,
The HI standard 9.8 "Intake Design for Rotodynamic Pumps" states that the Minimum Submergence for a horizontal bottom outlet from a tank can be given by S=D (1+2.3Fr) where D is the nozzle diameter and Fr is the Froude number
The Froude No. Fr = V / SQRT(g*D)
where
V = nozzle velocity
g = gravity constant.
My query is for a rectangular outlet nozzle, should I use an equivalent hydraulic diameter for D such as
dh = 2 a b / (a + b)
where
dh = hydraulic diameter
a = width of the duct (mm, in)
b = height of the duct (mm, in)
or do I just use the height ‘b’ of the rectangular nozzle as the value for D?
The HI standard 9.8 "Intake Design for Rotodynamic Pumps" states that the Minimum Submergence for a horizontal bottom outlet from a tank can be given by S=D (1+2.3Fr) where D is the nozzle diameter and Fr is the Froude number
The Froude No. Fr = V / SQRT(g*D)
where
V = nozzle velocity
g = gravity constant.
My query is for a rectangular outlet nozzle, should I use an equivalent hydraulic diameter for D such as
dh = 2 a b / (a + b)
where
dh = hydraulic diameter
a = width of the duct (mm, in)
b = height of the duct (mm, in)
or do I just use the height ‘b’ of the rectangular nozzle as the value for D?





RE: Minimum Submergence and Froude Number
Of course you could calculate it both ways and see how much the difference in velocity is then base your method on how conservative you want the result to be in case it doesn't work out like you expect (ie how expensive will it be to fix it).
RE: Minimum Submergence and Froude Number