4
plume characteristics
Marley ClearSky provide a means by which the plume leaving the tower can be made
less visible, or more buoyant, or both resulting in reduced ground fogging. This is done
by reducing the actual grains of moisture in the plenum airstream and at the same time
producing a stream of heated dry air that is mixed with the tower’s primary saturated
airstream prior to its exit from the tower. This results in desaturation of the plume to the
point where it does not cross into the fog region on its way back to ambient atmospheric
air conditions. In other words, little or no condensation will occur. Visibility reduction
is explained graphically in the Figure 2 ClearSky psychrometric diagram. The primary
airstream leaves the cooling tower’s wet section (fill) at condition 1 and it then passes
through the ClearSky heat exchanger where a secondary airstream enters the dry side
of the ClearSky heat exchanger, cooling the plume airstream and condensing a portion
of the moisture moving the airstream condition along the saturation line to condition 2.
The dry airstream gains heat but no moisture content and leaves at condition 3. These
two airstreams mix together along line 3–2 exiting the tower at condition 4. Returning
to atmospheric conditions along line 4–5, the plume is therefore neither dense nor
persistent. Plume characteristics depend upon the application of the ClearSky heat
exchanger modules to the cooling tower. In many cases, the plume can be made to
become invisible within one or two fan diameters above the top of the tower fan cylinder.
Figure 2
2
2
1
5
5
5
5
3
4
4
3
1
DRY BULB TEMPERATURE
WET-BULB OUT
OF WET SECTION
M
OI
STU
RE C
ONTE
NT
SA
TU
RA
TIO
IN
CU
RV
E
WET-BULB OUT
OF CLEARSKY
DRY-BULB OUT
OF CLEARSKY
MIX LINE TO AMBIENT
FAN EXIT POINT
PLUME DESIGN
POINT
VISIBLE PLUME
AREA
1
2
3
4
5