Cooling Tower Secrets
Almost all of today’s counterflow cooling towers have the same three problems that significantly downgrade their performance.
- Uneven water loading as a result of overlapping circular nozzles.
- Excessive wall water as a result of using circular nozzles.
- Inadequate water distribution systems.
Square is Better
Almost all cooling tower nozzles spray in a round pattern… and that’s a problem. A circle won’t cover a square unless it’s really oversized. So to compensate, companies design in an overlap in the spray pattern to eliminate these voids.
So why does that matter? First let me tell you how fill media works.
Cellular fill media consists of a series of corrugated flutes glued together to form a log. Each of the flutes in essence becomes a small cooling vessel specifically designed to accommodate 25% of the flute opening being allocated to water loading and the remaining 75% flute opening dedicated to air flow. Any deviation in this 1 to 3 ratio of air to water mixture will significantly degrade the performance of the cellular fill media.
So here is what happens when you overlap or flood the fill media.
As you can see in the graphic, the water loading becomes heavy where the overlap occur. This overlap creates a high pressure drop, restricting air flow in these areas. The blue arrows depict the restriction to the air flow resulting from the high pressure drop and the heavy water loading of the overlap.
The restrictions, caused by the overlap, cause the remaining air volume to be forced into areas where the water loading is light. Both the volume of air and the velocity will increase in these areas. The red arrows depicts the accelerating air flow exiting the fill media at high velocities. A gross waste of fan energy.
This same circular water pattern of the spray nozzles hits all the walls on the perimeter of the cooling tower, flooding the fill media in these areas.
What’s so bad about wall water? It had to be pumped to the top of the cooling tower. It flows down through the flooded areas of the fill media mixing with little air flow and as a result receiving little heat transfer. As with the nozzle overlaps, the air flow in this area is restricted and is directed into the adjacent fill media with less pressure. Another gross waste of both pump and air energy.
When the counterflow tower distribution systems was designed, the logic was to use the velocity pressure produced by the pump to create an equal static pressure at each nozzle resulting in a balanced water loading over the fill media.