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5.3
Absorption Distance B
N
The "absorption distance" (B
N
)
is defined as the distance from
the steam feed to where the steam is completely absorbed in the
treated air. Inside the absorption distance, steam is visible as
mist in the air stream.
Condensation may collect on anything installed inside the
absorption distance.
Although steam outside the absorption distance (B
N
) is com-
pletely absorbed, it is not yet evenly diffused in the duct. If you
plan to install any parts or devices inside the absorption dis-
tance, such as sensors or elbows, we recommend increasing
the absorption distance using the formulae below. The absorp-
tion distances required for certain installed fittings are distin-
guished by separate symbols and calculated as a multiplier of
the absorption distance B
N
.
The absorption distance has no fixed value, but depends on
many factors. These are depicted in the absorption distance
nomogram below.
5.3.1
Determining the Absorption Distance
To determine the absorption distance, the following parameters
are required:
•
Air humidity before humidification x
1
in g/kg.
•
Air temperature after humidification t
2
in °C (with steam
humidifiers the change in air temperature due to humid-
ification may be disregarded t
1
or t
2
).
•
Specific increase in humidity x in g/kg (can be deter-
mined in the h,x diagram)
•
quantity of steam introduced
in kg/h.
•
air speed w
L
in m/s in air duct
•
Total length l
D
of the steam manifold installed in the air
duct
Absorption Distance
B
N
for normal obstructions, such as sen-
sors, ventilators, outlets
B
c
= (1,5...2) x B
N
for fine filters, heat registers
B
s
= (2,5...3) x B
N
for particle filters
B
d
= (2,5...3) x B
N
for humidity sensors, duct humidistats
o
D
m
