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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