Unformatted text preview: 4.1.3 W51” 3E 319E Elementary Fluid Mechanics Momentum La oratory
Jame Date I]! ilﬁy 147"” Lab time 2/ Mfgw
AIR FLOW AROUND A BEND 1) Determine the volumetric flow rate and the average velocity in the bend. To apply the momentum ,equation for steady flow through the bend, it is necessary to know the inﬂow and the outﬂow
velocities. Since size of the bend is constant, the cross sectional average velocity is constant. The
acceleration comes primarily from changing the direction of the velocity, not from changing its
magnitude. The ﬂow rate can be determined by using the contracting nozzle above the elbow as a
ﬂow meter. One piezometer (#13 on the manometer board) is attached to the plenum chamber (pc,
Fig. l") and another one (#14) is attached at the downstream end of the contraction (in). Since the
pressure change is very small, the air may be assumed to be incompressible. Then, continuity gives @mm2Mmm A c 7’“ “(I [if(”l
Vin: prc ,7/1’ /'({'
Air:
Bernoulli’s equation may be applied along a streamline from pc to in since the effects of shear stress are negligble in
this short distance with rapid acceleration of the ﬂow. Thus, V2 V2
P0 _. in
WPC+ppc+p 2 ”ﬁfn'fpfn‘l'p 2
2 2 2
A V V'
ﬂpc‘l'PPC +p in i3W1}? +pin +pi
APC 2 2 Fig. 1 ~ Contracting Nozzle for
Me 'n
:(ppc_Pin) (2pc_za'n) ‘asun gQ For this apparatus, A?” >> A3,, and [ppc —pm)>> Azpc — Zin ). Thus, Vn x ghvpc ‘Pin) Procedure:
a) Read the piezometers for pc and in and then convert those readings into a pressure difference.
h14 = him I —4ﬁ cm 1113 = hpc — :3}; V5 CD1 ppc my. : mpg  aha/100 cm/rn = 98100;,”  hpcymo = Misﬁt ...
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 Fall '08
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 Fluid Dynamics, Elementary Fluid Mechanics Momentum La, Momentum La oratory, sectional average velocity

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