Page 178 - Mechanical Engineer's Data Handbook

FLUID MECHANICS 167

Power and eficiency A

Overall efficiency rt. = flmrtvrth
gHQ
Input power P = p -
‘IO
Inlet angles

Diffuser (fixed vanes):
Vf2
Inlet angle a = tan - -
VW2
a2
Outlet velocity V3 = V2 -
a3
Vane :
Vfl
Inlet angle fl, =tan- - (assuming no whirl)
VI1 Static and total eficiencies
v:
-.lbCI- Total head HI= no+-
I I Static head = H,
%
Static pressure=po=pgHo Total pressum=Pp,=pgHt

Static efficiency = ‘I, =o PQ Total efficiency = q1 = P~Q -
P P
4.1.2 Pump characteristics

Pump characteristics are plotted to a base of flow rate
for a fixed pump speed. Head (or pressure), power and
efficiency are plotted for dl&rent speeds to give a
family of curves. For a given speed the point at which
maximum efficiency is attained is called the ‘best
Pump volute etficiency point’ (B.E.P.). If the curves are plotted
nondimensionally a single curve is obtained which is
Q also the same for all geometrically similar pumps.
Velocity in volute V, = -
A4
where: A4=maximum area. Then:

A4
Pump outlet velocity V, = V, -
A0
where: A,=outlet area.
v:
v,’
Pressure head at outlet Ho= H --- K” 5
28
where: K,=dHuser and volute discharge coefficient.