Aug. 18, 2025
Agriculture
Figure 1. Plants typically rely on either an induced-draft crossflow (left) or counter-flow (right) design.
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Figure 1 shows schematics of the two most common types of industrial cooling towers, induced-draft crossflow and induced-draft counter-flow. Both of these use air to remove heat from water fed into the tower.
Ambient temperature and humidity influence performance, and typically 65–90% of heat transfer in a cooling tower comes from evaporation of a small portion (1–3%) of the recirculating water. Thus, an underlying guideline for all cooling towers is to enhance air/water contact. In the beginning, this was accomplished through the use of splash fill — a series of wooden slats placed in a staggered formation below the water spray nozzles. As water impinges upon the slats, it breaks into small droplets that increase the surface area.
Fill has evolved significantly from that rudimentary splash fill design. Most cooling towers now utilize film fill to enhance air/water contact. Film fill, as the name implies, induces the cooling water to form a film on the material surface. The filming mechanism maximizes liquid surface area. A guiding principle behind fill design and selection “is to increase air-to-water contact, driving up convection and evaporative cooling while reducing pressure drop in the system” [1]. Fills generally are made of polyvinyl chloride because of its low cost, durability, good wetting characteristics and inherently low flame spread rate.
The choice of fill design in large measure depends upon the fouling tendencies of the cooling water. Figure 2 illustrates a variety of fill designs ranging from modern splash fill to very high efficiency material.
The most basic and least expensive is plastic splash fill (Figure 2a). An advancement on this technology is “wire frame” fill. In one type of wire-frame design, water film cascades on the strand surface; cooling occurs predominantly via film generation, with droplet generation only incidental. This fill typically comes in a modular cross-fluted design. The other wire frame design uses a multitude of integrated drip points to create a compact volume of droplets (2b). These “modular splash” (M/S) fills usually have offset flute geometry and are inherently more fouling resistant than cross-fluted fills. Reference 1 provides more information.
The others options consist of film fills. These have air/water passageways called flutes. A variety of flute configurations are available, with each reflecting a different tradeoff between thermal performance and fouling resistance.
Vertical film fills such as vertical flutes (VF, 2c) offer a straight path for water and air flow. Thermal performance is lower than that of higher efficiency designs but VF fill has excellent anti-fouling characteristics.
XF stand-off fill (2d), which is made specifically for crossflow cooling towers, boasts a high specific surface area and moderate-to-good anti-fouling tendencies depending upon water loading.
Types Of FillFigure 2. Choice of fill largely depends on the fouling tendencies of the cooling water. Source: Brentwood Industries.
Offset flutes (OF, 2e) also have high specific surface area, and force the water and air through a moderately tortuous path. Thus, anti-fouling characteristics are moderate, too.
Cross flutes (CF, 2f) typically provide high specific surface area and high thermal performance but exhibit poor anti-fouling characteristics due to the geometry that forces many deviations to the flow path.
Flute spacing significantly affects fill performance; smaller spacing increases the surface area but also raises the potential severity of fouling.
Many investigators have pointed to bio deposits as the key trigger of film fill fouling. The scenario for fouling is: biofilms form on the fill surface and collect suspended solids from the cooling water due to the inherent adhesive properties of the bacterial secretions.
The velocity of the water film passing over the deposit surface influences the stability of bio deposits. Higher water velocities minimize biofilm thickness. So, fill manufacturers have developed designs that maximize water film velocity and the resulting high shear stress. The flute geometry of these low fouling fills has a vertical orientation as opposed to the angled orientation (cross flute) of high efficiency fills. These higher water velocity designs exhibit lower thermal performance than their CF counterparts.
CF fills provide maximum surface area for heat transfer but impart a higher pressure drop through the tower than other designs. Also, the lower water film velocity developed within these fills can lead to low flow regions, increasing the fouling potential.
Selecting the proper design requires a careful evaluation of water conditions. Table 1 outlines guidelines for fill selection with various quality waters, ranging from <1,000 ppm to <25 ppm of total suspended solids (TSS) and 0 to <50 ppm of oil and grease.
That table underscores the impact of biological control on fill selection. Yet, as I personally can attest, microbiological control in cooling systems, even once-through networks, can be a challenge. However, suitable care in the design and selection of chemical feed programs and makeup-water pretreatment equipment may enable use of higher-efficiency fills in applications where they otherwise wouldn’t make sense.
Oxidizing biocide treatment is essential for all cooling water systems. Chlorine, usually supplied as bleach or generated on-site, is the most common choice, although the effectiveness of chlorine rapidly diminishes as the pH rises above 7.5. Many natural waters have a pH near 8, which often leads to selection of alternative oxidizers, most notably chlorine-activated bromine, chlorine dioxide, monochloramine and monobromamine. In many cases, oxidizer feed is limited to two hours per day, which gives microbes time to settle and form colonies during off times. A supplemental feed of a non-oxidizing biocide, say, on a once-per-week basis, can quite effectively control microorganisms. Table 2 lists properties of some of the most common non-oxidizers.
Careful evaluation of the microbial species in the cooling water is necessary to determine the most effective biocides. Do not test, let alone use, any of these chemicals without approval from the appropriate regulating agency. They must be incorporated into the plant’s National Pollutant Discharge Elimination System permit. Also, as with all chemicals, safety is an absolutely critical issue when handling the non-oxidizers.
The use of alternatives to fresh water for plant makeup is becoming more common. One increasingly popular source, either by choice or mandate, is effluent from a publicly owned treatment works, i.e., municipal wastewater treatment plant discharge. These streams often have significant concentrations of ammonia, nitrite/nitrate, phosphate and organics, or in the industry vernacular, “bug food.” Untreated, such makeup water can cause explosive growth of microorganisms in cooling systems. Sophisticated pretreatment of the plant makeup usually is necessary, with two increasingly common options being membrane bioreactors and moving-bed bioreactors.
Another factor that influences fouling is the suspended solids’ concentration in the water. Any microbiological colonies that do become established in fill or heat exchangers typically secrete a slimy film for protection. This slime naturally captures silt. A treatment method that is regularly recommended for cooling towers — but often isn’t adopted — is sidestream filtration. Information about sidestream filtration is readily available from a number of sources, most notably the Cooling Technology Institute.
BRAD BUECKER is a senior technical publicist for ChemTreat, Glen Allen, Va. him at [ protected].
ACKNOWLEDGEMENTS
The author wishes to acknowledge Rich Aull, retired from Brentwood Industries and now president of Richard Aull Cooling Tower Consulting, LLC, for providing substantial assistance with this article, and Bill Miller of Brentwood Industries for photos of the various types of fill.
REFERENCES
1. Zaorski, A. and W.C. Miller, “A Study on Bio-Fouling Characteristics of Contemporary Trickle and Modular Splash Fills,” presented at the Cooling Technology Institute Annual Conference, New Orleans, La. (February ).
2. Wallis, J. and R. Aull, “Improving Cooling Tower Performance with Thermal Fills,” Process Cooling & Equipment, March/April .
Cooling towers are an integral component of many industrial and commercial facilities. They serve the important purpose of removing excess heat from industrial processes or air conditioning systems. In order to achieve this, cooling towers rely on a process of evaporation and heat transfer. However, in order for cooling towers to function properly, they require fill. In this article, we will explore the purpose of filling in a cooling tower.
Fill refers to the material that is used to fill the space inside a cooling tower. The fill is a critical component of the tower because it provides a large surface area for water to flow over, which facilitates the transfer of heat from the water to the air. Fill is typically made of PVC or another plastic material, and it is designed to be lightweight and durable.
The primary purpose of filling in a cooling tower is to increase the surface area of the water that is exposed to the air. As water flows over the fill material, it spreads out into a thin film, which allows for maximum contact with the air. This increased surface area maximizes the amount of heat that can be transferred from the water to the air.
The fill material also creates a large amount of turbulence in the water as it flows through the tower. This turbulence helps to break up any stagnant areas within the water and ensures that all parts of the water are exposed to the air. This, in turn, improves the overall efficiency of the cooling tower.
Another important purpose of filling in a cooling tower is to minimize the amount of water that is lost through evaporation. When water is sprayed onto the fill material, it is broken up into droplets, which helps to minimize the amount of water that is lost through evaporation. This is important because evaporation can be a major source of water loss in a cooling tower, and minimizing this loss can help to reduce operating costs.
Further reading:For more information, please visit smc water tank.
There are two main types of fill that are commonly used in cooling towers: film fill and splash fill. A film fill is a type of fill that is designed to create a thin film of water over the surface of the fill material. This film allows for maximum contact between the water and the air, which maximizes the efficiency of the cooling tower. Splash fill, on the other hand, is designed to break up the water into small droplets as it flows over the fill material. This creates a large amount of turbulence within the water and ensures that all parts of the water are exposed to the air.
If you’re in the market for cooling tower fill, choosing the right type is critical to ensure optimal system performance and long-term reliability. Here are key factors that industrial buyers and engineers should consider:
Different materials serve different working environments:
PVC (Polyvinyl Chloride): Offers good chemical resistance and is cost-effective. It is used in over 80% of standard cooling tower installations, especially in HVAC and light industrial applications.
PP (Polypropylene): Can withstand higher temperatures (up to 100–120°C compared to PVC's ~60°C). Ideal for applications with hot process water or strong chemicals.
Wood or Metal Fill: Less common today but still in use for legacy systems or high-load industrial cooling towers.
We offer a wide range of fill materials – click here to view all fill products.
Film Fill: Designed with thin corrugated sheets that create a large surface area for water film formation. This type can improve heat exchange efficiency by up to 30% in clean water systems.
Splash Fill: Breaks water into droplets and resists fouling—ideal for systems using untreated or recirculated water. Increases system reliability in high-dust or sediment-prone environments.
Modular Block Fill: Used in regions where maintenance access is limited. Reduces cleaning time by 40–60% compared to traditional sheet fill.
Each fill type optimizes efficiency and operational stability depending on water quality and system type.
Ask for the KaV/L value—a widely recognized metric for fill thermal performance:
KaV/L ≥ 0.2 is considered high-performance for standard industrial applications.
Using high-efficiency fill can reduce outlet water temperature by 2–5°C, resulting in:
5–15% lower chiller energy consumption
Better equipment lifespan and reduced operational load
We provide thermal performance data sheets on request for all our fill products.
Fill packs are available in various lengths (0.5–2 meters), thicknesses (100–600mm), and flute sizes (12–30mm) to match different tower models and flow rates.
We support custom designs for non-standard towers or space-limited installations.
Need a custom fill pack? Contact us now to discuss your project needs.
Average service life ranges from 3 to 7 years, depending on material, operating temperature, and water quality.
Using UV-resistant and anti-microbial additives can extend service life by up to 20–30% in outdoor or high-temperature environments.
For towers in regions with hard water or dust, modular fill design reduces cleaning downtime by up to 50%.
Long-term performance means fewer replacements and lower lifecycle cost.
Ensure the fill is compatible with:
Your cooling tower configuration: Crossflow or Counterflow
Water treatment process and filtration level
Airflow pattern and spray system
Not sure what you need? Our technical engineers provide free evaluation reports based on your tower specs.
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