In counterflow cooling towers, where air moves vertically upward against the falling water, the packing (also called fill) is the critical component that maximizes heat and mass transfer. Its primary functions are to create a large surface area for water-to-air contact and to delay water fall to increase contact time.
Here are the main types of packings used, categorized by their fundamental design:
1. Splash Packing (Film-Forming)
This type relies on breaking the water into small droplets by causing it to splash repeatedly over the packing elements. It creates a large surface area through droplet formation.
- Design: Consists of spaced bars, grids, or slats arranged in staggered patterns.
- Common Materials: PVC, wood, polypropylene.
- Examples:
- Wood Grids: Traditional, rectangular slats.
- Bars or Splash Grids: Horizontal or vertical arrays.
- Honeycomb Splash Grids: More modern, efficient grid designs.
- Advantages:
- Less prone to fouling and scaling (good for hard or dirty water).
- Easy to clean.
- Good structural strength.
2. Film Packing
This is the most common and efficient type in modern cooling towers. It spreads the water into a thin, continuous film over a large, closely-packed surface area, providing excellent contact with the air.
- Design: Features closely spaced, corrugated sheets or structured surfaces that guide water flow.
- Common Materials: Primarily PVC sheets, CPVC (for higher temperatures), polypropylene.
- Examples:
- Vertical Film Fill: Corrugated sheets arranged vertically. Most common for counterflow towers.
- Horizontal Film Fill (for crossflow): Less common in true counterflow.
- Advantages:
- Very high thermal efficiency (more cooling in less volume).
- Lower pumping head as water flows by gravity.
- Generally lower air-side pressure drop than splash fill.
3. Trickle or Grid Packing
A hybrid/modern type that functions as both splash and film fill. It’s designed to be highly efficient while maintaining some of the fouling resistance of splash fill.
- Design: Often a three-dimensional grid or open honeycomb structure with a textured surface.
- Common Materials: PVC, polypropylene.
- Advantages:
- Good balance between efficiency and fouling resistance.
- Lower pressure drop than traditional splash grids.
Excellent structural integrity (often used in large, industrial towers).