MIL-HDBK-1011/2
APPENDIX C (continued)
1.2.2
Flow Due to Wind--Openings in Series
1.2.2.1
Flow Volume.
To calculate volume of flow for openings in series
use Equation 11.
EQUATION:
Q
=
[(Cp1 - Cp2 + 1) Vref]
(11)
))))))))))))))))))))))))))))))))
1/2
2
2
2
2
2
2
[1/(C
*A )+1/(C
*A )+...+1/(C
*A )]
d1
1
d2
2
dn
n
where
Cp1
=
pressure coefficient near most windward opening
Cd1
=
discharge coefficient near most windward opening
Cp2
=
pressure coefficient near next most windward opening
Cd2
=
discharge coefficient near next most windward opening
A1
=
area of most windward opening
A2
=
area of next most windward opening
Vref
=
wind velocity at reference height at which pressure
coefficients were taken.
1.2.2.2
Flow Velocity. To determine the mean flow velocity near the
openings, use Equation 12.
EQUATION:
Vo
=
Q / effective area of opening = Q / An cos alpha
(12)
where
Vo = mean flow velocity near the opening, ft/min (m/sec)
= volumetric flow rate (from Equation 8), cfm (m3/sec)
Q
An = area of opening, ft2 (m2)
alpha
=
angle of incidence of the wind
Discharge Coefficient for Varying Wind Angles. The discharge
1.2.2.3
coefficient for varying wind angles is given by Equation 13.
EQUATION:
Cd = Cd (perpendicular winds) cos alpha
(13)
1.2.3
Flow due to thermal forces. If there is no significant internal
resistance due to a partitioned interior, and assuming indoor and outdoor
temperatures are close to 80deg.F (26.7deg.C) and inlet and outlet openings
are
equal, the flow due to stack effect is given by Equation 14.
EQUATION:
Q = CKA [g delta h (ti - to) / ti]
(14)
airflow, cfm (m3/sec)
where
Q
=
C
=
unit conversion factor, 60.0 for Q in cfm and 1.0 for
Q in m3/sec
K
=
discharge coefficient for the openings, 0.65 for
multiple openings and 0.40 for single opening in a room
free area of inlets, ft2 (m2)
A
=
gravitational constant, 32.2 ft/sec2 and 9.81 m/sec2
g
=
delta h
=
height from bottom to top of opening for rooms with
115
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