Eclipse Combustion Engineering Guide - Burnerparts

CHAPTER 1 – ORIFICES & FLOWS
COEFFICIENTS OF DISCHARGE FOR VARIOUS TYPES OF ORIFICES
Sharp Edge
C d = 0.60
Reentrant
0.72
Round Edge
0.97
Short Pipe
0.82
Converging
depends on angle. See
curve at right.
Coefficient of Discharge (C d )
0.95
Orifices and Nozzles Discharging from Plenum
0.93
0.91
0.89
0.87
NOTE: The loss is least at 13˚
0.85
0.83
0 2 4 6 8 10 12 14 16 18 20 22 24
Angle of Convergence in Degrees
ORIFICE FLOW FORMULAS
The flow of air or gas through an orifice can be determined 3.Effect of Changes in Operating Conditions on Pressure
Drop Across an Orifice–General Relationship:
by the formula
h
Q = 1658.5 x Ax C d g
h 2
= Q 2 2 x A 1 2 x C d1 2 x g 2
h 1
(
Q 1
) (
A 2
) (
C d2
)
g 1
where Q =flow, cfh
Again, if any of the factors in this equation are unchanged
A =area of the orifice, sq. in. (see Pages 57 & 58) from Condition 1 to Condtion 2, they can be dropped out to
C d =discharge coefficient of the orifice
form simplified relationships:
(see above)
3a.Pressure Drop Change vs. Flow Change
h =pressure drop across the orifice,″ w.c.
h
g =specific gravity of the gas, based on standard
2
= Q 2 2
h
air at 1.0 (see Pages 19, 20, & 22 thru 24.)
1
(
Q 1
)
This is the square root law, stated another way.
1. Sizing Orifice Plates
To calculate the size of an orifice plate, this equation can 3b.Pressure Drop Change vs. Orifice Area Change
be rearranged as follows:
h 2
= A 1 2
h
A= Q x
g
1
(
A 2
)
1658.5 x C d
h
3c.Pressure Drop Change vs. Specific Gravity Change
h 2
= g 2
2. Effect of Changes in Operating Conditions on h 1
g 1
Flow through an Orifice – General Relationship This relationship may not apply where specific gravity has
Q 2
= A2 x Cd2 x h2 x g 1
been changed by a change in gas temperature. See Page 25.
Q 1 A 1 C d1 h 1
g 2
4. Effect of Changes in Gas Temperature on Flow and
If any of the factors in this relationship remain constant Pressure Drop through an Orifice
from Condition 1 to Condition 2, they can be dropped out of Raising a gas’s temperature has two effects – it increases
the equation, yielding these simplified relationships. Each of the volume and decreases the specific gravity, both in proportion
to the ratio of the absolute temperatures. If we are con-
them assumes only one factor has been changed.
2a.Flow Change vs. Orifice Area Change
cerned with changes in mass flows (scfh), these relationships
Q 2
= A must be used:
2
Q 1 A 1
4a.Flow Change vs. Temperature Change
2b.Flow Change vs. Pressure Drop Change
Q 2
= T ADS1
Q 2
= h Q 1 T ABB2
2
Q 1 h 1
4b.Pressure Drop Change vs. Temperature Change
This is the so-called “square root law.”
h 2
= T ABS2
h 1 T to maintain constant scfh
ABS1
2c.Flow Change vs. Specific Gravity Change
Q 2
= g 1
Q 1
g 2
4