In short: Cooling tower fill increases the contact between water and air. Film fill spreads water into thin films over closely spaced sheets. It gives much higher heat rejection per unit volume than splash fill, but it is far more susceptible to fouling, scaling and biological growth (US DOE/FEMP). Splash fill breaks the falling water into droplets over bars or open modules. It gives lower thermal performance per unit volume but tolerates dirty water, suspended solids and debris much better. Choose film fill for clean, well-treated water. Choose splash or fouling-resistant fill for compromised water, and evaluate fill on life-cycle performance, not only its as-new rating.
What fill does
In a wet cooling tower, hot water is distributed over the fill while air moves through it, either across the flow (crossflow) or up against it (counterflow). Most heat is removed by evaporation. The fill's job is to maximize the water surface area and contact time with the air while keeping airflow resistance acceptable. See our FRP Cooling Towers Guide for the full tower anatomy.
Film fill
Film fill consists of thin formed sheets, usually PVC or polypropylene, bonded into packs with flutes (channels). Water spreads over the sheet surfaces as thin films while air passes through the channels.
Advantages:
- High heat transfer surface per unit volume
- Greater heat rejection than splash fill for the same tower volume (DOE/FEMP)
- Allows more compact towers or more cooling within an existing tower
Limitations:
- Narrow channels can plug with suspended solids, scale and biofilm
- Fouled fill adds weight. The US DOE notes that in severe cases fouled fill can collapse portions of the fill or tower structure
- Requires good water treatment and routine inspection
Flute geometry matters. A cooling tower fill manufacturer reports that the closer to vertical a film fill's flutes are, the more fouling resistant the fill tends to be, because higher water velocity and shear discourage biological growth. Cross-fluted fills give high thermal performance but foul more easily. Offset and vertical-fluted designs trade some thermal performance for fouling resistance.
Splash fill
Splash fill uses bars, grids or open modules arranged in levels. Water falling through the fill repeatedly hits the elements and breaks into droplets, creating surface area as it falls.
Advantages:
- Open geometry is much less prone to plugging
- Suited to water with high suspended solids, mud, silt, dust or process contaminants
- Easier to inspect and clean
Limitations:
- Lower heat transfer per unit volume, so taller or larger fill sections are needed for the same duty
- Older towers may use wood splash bars. Modern bars are plastic or FRP
The same manufacturer describes splash bar fills as the choice when compromised waters are used for make-up, when there is a high degree of dust or sand, or when process contaminants could harm film-type fills.
Fouling: as-new rating vs real performance
A fill's as-new thermal rating can mislead if the water will foul it. In a 21-week fouling test at total suspended solids of 375 ppm, the same manufacturer compared vertical-offset modular splash fill with cross-fluted trickle fill (a wire-frame splash fill vs a cross-fluted film fill in the same manufacturer's test, so the result is specific to those fills). The cross-fluted fill gained over 400% more weight. When the fouled packs were modeled in a tower, the splash fill lost only about 2% of tower capability, while the cross-fluted fill lost about 18% (a cooling tower fill manufacturer, CTI 2017 paper summary).
The lesson is that the fill should be selected for the water it will actually see over its life.
Comparison table
| Factor | Film fill | Splash fill |
|---|---|---|
| Heat transfer mechanism | Thin water films on sheets | Droplets from repeated impacts |
| Thermal performance per volume | High | Lower |
| Fouling resistance | Low to moderate (depends on flute design) | High |
| Water quality needed | Clean, well-treated | Tolerates suspended solids and debris |
| Fill height for same duty | Lower | Higher |
| Inspection and cleaning | Harder (closed channels) | Easier (open structure) |
| Typical uses | HVAC, clean process water | Steel mills, pulp and paper, dirty make-up water |
How to choose
- Test the water. Suspended solids, oil and grease, biological activity, scaling tendency and make-up water source.
- Assess water treatment. Will biocide and scale control be reliable for the tower's life?
- Check the environment. Dust, sand, leaves or process fallout.
- Compare life-cycle performance. Include expected fouling, cleaning and replacement, not only the as-new rating.
- Check the tower. Fill height available, air flow, structural load capacity for wet and fouled fill.
- Consider hybrids. Fouling-resistant film fills, or combinations of splash and film zones, can suit intermediate water quality.
FRP structures and fill support
Fill sits on supports inside the tower casing. FRP towers and support structures resist the wet, chemically treated environment that corrodes carbon steel. FIBROVX supplies cooling tower fill media and FRP cooling towers. See the cooling towers and components collection.
Customization
We size fill to your tower dimensions, water flow and duty. We can supply replacement fill for existing towers based on measured dimensions, or include fill in a new FRP tower. Tell us your water quality so we can recommend a suitable fill type. Thermal performance must be confirmed by tower design calculations for your conditions.
Need a quote or a drawing check?
FIBROVX manufactures FRP products in our own factory in China and builds every item to order: sizes, resin system, color, molds and OEM branding. Send your application, dimensions or drawing, quantity and destination port.
Request a QuoteKey terms
- Flute: A channel formed in a film fill sheet through which air and water pass.
- Drift: Water droplets carried out of the tower by the air.
- Make-up water: Water added to replace evaporation, drift and blowdown.
FAQ
Is film fill always better?
No. It gives more cooling when the water is clean. With dirty water it can foul, lose performance and add dangerous weight.
What causes film fill fouling?
Suspended solids, biological growth (biofilm), scale and oil. These often combine: solids stick to biofilm and build up.
Can I replace splash fill with film fill?
Sometimes, to gain capacity, but only if the water quality and treatment are suitable and the tower structure and air system are checked.
How often should fill be inspected?
The US DOE recommends routine inspection of film fill to keep it clean and free of debris, scale and biological activity. Frequency depends on water quality.
What is fill made of?
Film fill is usually PVC or polypropylene sheet. Splash bars may be plastic, FRP or, in older towers, wood.
Related guides
- FRP Cooling Towers Guide
- FRP Chemical Resistance Guide
- What Is FRP?
- Technical Resources: datasheets and drawings on request
- Cooling Tower Fill Fouling: Causes, Cleaning and Replacement
- Cooling Tower Sizing Basics: Range, Approach and Wet-Bulb
- Industries we serve
Sources
- US DOE FEMP, "Cooling Towers: Understanding Key Components of Cooling Towers and How to Improve Water Efficiency" (film fill heat rejection vs splash fill; fouling susceptibility; collapse risk; routine inspection): https://www1.eere.energy.gov/femp/pdfs/waterfs_coolingtowers.pdf
- A cooling tower fill manufacturer, "Does flute geometry and the mode of heat transfer (trickle vs. splash) affect fouling resistance…" (21-week test, 375 ppm TSS, >400% weight gain, 2% vs 18% capability loss; vertical flutes resist fouling)
- A cooling tower fill manufacturer, "Cooling Tower Splash Fills" (applications for splash bar fills)