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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. Within the absorption distance,
steam is visible as mist in the air stream.
Condensation may occur on anything
installed within the absorption distance.
Although steam outside the absorption dis-
tance (B
N
) is completely absorbed, it is not
yet evenly diffused in the duct. If you plan to
install any parts or devices inside the absorp-
tion distance, such as sensors or elbows, we
recommend increasing the absorption dis-
tance using the formulae below. The absorp-
tion distances required for certain installed
fittings are distinguished by separate sym-
bols 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 nomo-
gram below.
5.3.1 Determining the Absorption
Distance
To determine the absorption distance, the fol-
lowing 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
humidification may be disregarded
t
1
or t
2
)
•
Specific increase in humidity x in
g/kg (can be determined 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
Length I
D
of the usable steam manifold
depends on the dimensions of the air duct.
The length of the absorption distance can be
reduced by using multiple steam manifolds
(also see section on the steam manifold).
Method:
Graphically determine absorption distance
B
N
using the absorption distance nomogram
(also see Section „Absorption Distance
Nomogramm“). Enter the value of the param-
eters enumerated above into the respective
quadrants. The resulting point of intersection
indicates the value of the desired absorption
distance B
N
.
Notes:
Air humidity before humidification x
1
:....[g/kg]
Air temperature after humidification t
2
:.....[°C]
Specific increase in humidity x:...........[g/kg]
Quantity of steam introduced
:.........[kg/h]
Air speed W
L
:..........................................[m/s]
Total length of steam manifold l
D
:...........[mm]
o
D
m
o
D
m
Absorption Distance
B
N
for normal obstructions
such as sensors, ventila-
tors, outlets
B
c
= (1.5...2) x B
N
for fine fiters, heat regis-
ters
B
s
= (2.5...3) x B
N
for particle filters
B
d
= (3...5) x B
N
for humidity sensors,
duct humidistats
