Indirect heat exchanger
A heat exchange apparatus is provided with an indirect evaporative heat exchange section. An evaporative liquid is downwardly distributed onto the indirect section to indirectly exchange sensible heat with a hot fluid stream flowing within a series of enclosed circuits which comprise the indirect evaporative heat exchange section. An ideal flow rate for such evaporative liquid is between 2.0 and 4.0 gallons per minute per square foot of top surface area of the indirect heat exchange section.
1. A method of operating an indirect heat exchanger comprising:
providing an indirect heat exchanger comprising:
a plurality of coils having length sections and bend sections,
a fan to draw air across the plurality of coils,
a water distribution system located above the plurality of coils and comprising
a series of discharge sections, an inlet header connected to the series of discharge sections,
a plurality of openings in each discharge section that allow water to be distributed downwardly over the plurality of coils and a sump to collect the water after passing over the plurality of coils,
wherein the water distribution system also comprises an exit opening in the sump, and a pump connected to the exit opening, and a return line to supply the water from the sump to the inlet header of the water distribution system, with the pump having a capacity at any given time results in water being discharged from the water distribution system onto the plurality of coils to provide a density zone profile (DZP) according to:
DZP= C f *N ROWS*[( NCKTS*D P )/ C W ]^2 Equation 1
Where:
DZP=Density Zone Profile Number
C f =correction factor for fins described in table 1 below
NROWS=number of tubes fed from top to bottom
NCKTS=number of circuits in a casing width
D P =projected tube diameter, inches
C W =casing width, inches
Wherein DZP is the density zone profile of the plurality of coils,
TABLE 1
% of Rows that
C f (Finned
are finned
Description
Correction factor)
0%
None of the tubes
1.0
are finned
5% < finned rows < 33%
1.3
33% < finned rows < 66%
1.6
>66% finned rows
Most or all rows
2.0
are finned
wherein a water distribution spray water flow rate is set to:
greater than 4 gpm/ft 2 when DZP is less than 10, and
between 2 to 4 gpm/ft 2 when DZP is greater than or equal to 10.
2. The method of claim 1
further comprising a controller to vary the pump speed and pumping capacity and thusly vary the water discharge rate.