Fogging Web™
Fogging Web™: An Engineered Approach to Adiabatic Cooling of Air-Cooled Heat Exchangers
Air-Cooled Heat Exchangers (ACHEs) are designed around defined ambient conditions. When the actual ambient temperature rises above the design point, the available temperature difference between the process fluid and the cooling air decreases.
The result can be familiar to operators: increasing process outlet temperatures, reduced condensing capacity, production constraints and, in some applications, summer derating.
Increasing airflow can provide additional cooling capacity, but only within the aerodynamic and mechanical limitations of the existing air cooler.
An alternative approach is to improve the condition of the air itself before it enters the Air-Cooled Heat Exchanger.
This is the principle behind Fogging Web™.
By introducing ultra-fine water droplets into the incoming air stream, part of the sensible heat of the air is converted into latent heat through evaporation. The resulting reduction in dry-bulb temperature increases the available temperature difference across the heat exchanger and can therefore increase the achievable heat rejection capacity.
However, effective adiabatic cooling requires more than installing spray nozzles beneath an air cooler.
It requires an engineered system.
1. Performance Engineered
Every Air-Cooled Heat Exchanger behaves differently.
ACHE geometry, number of fans, airflow, fan diameter, bundle dimensions, design temperatures, process duty, elevation and local climatic conditions all influence the potential benefit of adiabatic inlet-air cooling.
For this reason, Fogging Web™ is not approached as a standard spray system.
Each application starts with the thermal requirements of the Air-Cooled Heat Exchanger.
The existing operating condition can be evaluated using process data, ambient measurements and, where required, field airflow measurements. From this information, the required reduction in inlet-air temperature and associated water evaporation rate can be determined.
Psychrometric conditions are particularly important.
The achievable temperature reduction depends not only on dry-bulb temperature, but also on relative humidity. Hot and relatively dry ambient air provides significantly more evaporative cooling potential than air that is already close to saturation.
The objective is therefore not to introduce as much water as possible.
The objective is to introduce the required amount of water under the available atmospheric conditions to achieve the targeted cooling performance.
2. Modular Per Fan
Large Air-Cooled Heat Exchangers can contain multiple fans operating across one or several bays.
Treating the complete air cooler as one large adiabatic system can unnecessarily reduce operational flexibility.
Fogging Web™ therefore uses a modular fan-by-fan concept.
Each fan can be equipped with its own Fogging Web module positioned in the incoming airflow.
This allows the installation to be configured around the actual cooling requirement. Depending on the application, Fogging Webs can be installed beneath all fans or only beneath selected fans where additional cooling capacity is required.
The modular concept also allows the system to follow the existing ACHE layout rather than requiring substantial modification of the air cooler itself.
For larger installations, this provides another important advantage: capacity can be expanded progressively if operating requirements change in the future.
3. High-Pressure Atomization
Droplet formation is one of the most important parameters in an adiabatic cooling system.
Fogging Web™ uses high-pressure atomization to generate ultra-fine water droplets and distribute them across the incoming airflow.
Smaller droplets provide a high surface-area-to-volume ratio, which promotes rapid heat and mass transfer between the water and surrounding air.
The engineering objective is to maximize evaporation while the droplets travel with the incoming air towards the fan and heat exchanger.
As water evaporates, energy is extracted from the air as latent heat. This lowers the dry-bulb temperature of the incoming air while increasing its humidity ratio.
Ideally, the evaporation process takes place before the air reaches the finned-tube bundle.
This distinction is important.
Fogging Web™ is designed as an inlet-air cooling system, rather than as a system intended to wet the heat-transfer surface.
4. Engineered Water Distribution
Generating small droplets alone is not sufficient.
They also need to be distributed effectively across the airflow.
A fan inlet represents a substantial cross-sectional area and can handle a very large volume of air. Concentrating the complete water flow in only a small section of this area can create uneven evaporation and localized moisture concentrations.
The radial geometry of Fogging Web™ distributes multiple atomization points across the fan inlet area.
The number, position and capacity of the atomization points can be selected according to the required water flow and ACHE geometry.
The objective is a controlled and distributed introduction of water into the incoming air stream rather than a concentrated spray pattern.
This becomes increasingly important as fan diameter and required water flow increase.
5. Maintenance Friendly
Performance improvement equipment should not unnecessarily complicate maintenance of the existing Air-Cooled Heat Exchanger.
Access beneath ACHE fans may be required for inspection and maintenance of fan assemblies, bearings, gearboxes, belts, motors, structures and other mechanical components.
Fogging Web™ modules are therefore designed with maintainability in mind.
Individual Fogging Webs can be disconnected and removed when access to a specific fan section is required.
Because the system is modular, other Fogging Web sections can remain available while maintenance activities are performed on an individual module or fan position, subject to the operating requirements of the installation.
The objective is simple:
Improve cooling performance without turning the adiabatic system into a maintenance obstacle.
6. Flexible Water Supply
Not every industrial site has the same utilities available.
Some facilities have a suitable existing high-pressure water system, while others only have a conventional low-pressure water supply available near the ACHE.
Fogging Web™ can therefore be configured around both situations.
Where no suitable high-pressure source is available, the system can be supplied with a purpose-engineered high-pressure pump unit.
Where an existing high-pressure water source is available, integration may be possible provided that the pressure, flow capacity and water quality are technically suitable for the atomization system.
This flexibility can reduce unnecessary duplication of equipment and allows the Fogging Web concept to be adapted to both existing brownfield facilities and new installations.
Water quality remains an important engineering consideration.
Filtration, dissolved solids, hardness, chlorides and other water characteristics should be reviewed during system engineering to ensure reliable nozzle performance and long-term system integrity.
7. Modular & Rapid Deployment
ACHE modifications frequently take place in operating plants where shutdown windows and installation time are limited.
Fogging Web™ is therefore based on a modular, pre-assembled concept.
Where practical, components can be assembled before arriving on site, reducing the amount of fabrication and assembly required underneath the air cooler.
This provides several practical advantages:
- compact transportation;
- reduced on-site assembly;
- efficient installation;
- repeatable module configuration;
- easier replacement of individual sections; and
- straightforward future expansion.
For brownfield ACHE applications in particular, minimizing site work can be just as important as the thermal performance of the final system.
8. In-House Engineering & Manufacturing
The performance of an atomization system depends on the interaction between multiple components.
Mechanical geometry, hydraulic distribution, nozzle selection, operating pressure, water flow and installation arrangement all influence the final result.
Key Fogging Web™ components are therefore engineered and manufactured in-house.
Keeping engineering and manufacturing closely connected provides greater control over component geometry, quality, customization and lead times.
More importantly, it allows the mechanical design of the Fogging Web to remain directly connected to the thermal requirements established during the ACHE engineering phase.
The system is therefore developed as part of an air-cooler performance solution rather than as an isolated collection of spray components.
9. Designed Around Existing Equipment
For many operating facilities, replacing or substantially modifying an existing Air-Cooled Heat Exchanger is neither practical nor economically attractive.
A key principle behind Fogging Web™ is therefore to utilize as much of the existing equipment as possible.
The air cooler structure, fan system and heat-transfer bundle remain the foundation of the cooling system.
Fogging Web™ adds another performance variable:
inlet-air temperature.
Instead of relying exclusively on additional airflow or additional heat-transfer surface, the system improves the thermodynamic condition of the cooling medium entering the exchanger.
This makes adiabatic inlet-air cooling particularly interesting for installations where cooling limitations primarily occur during the hottest periods of the year.
10. Measurable Performance
Perhaps the most important characteristic of an engineered ACHE modification is that its effect should be measurable.
Installing equipment is not the end of the process.
Where required, Fogging Web™ can be incorporated into a broader ACHE performance improvement program.
A typical approach can include:
Measure → Analyse → Engineer → Install → Verify
Before installation, field measurements and operating data can establish the existing condition of the air cooler.
Engineering analysis can then estimate the effect of reducing the inlet-air temperature under representative ambient conditions.
After installation, measurements can be repeated with Fogging Web™ operating.
Depending on the application, relevant parameters may include:
- ambient dry-bulb temperature;
- relative humidity;
- air temperature downstream of the Fogging Web;
- ACHE inlet-air temperature;
- process inlet and outlet temperatures;
- airflow;
- process flow;
- fan operating condition; and
- overall heat rejection.
This allows the actual improvement to be compared with the predicted performance.
Because ultimately, the relevant question is not:
“Is the fogging system operating?”
It is:
“How much additional ACHE performance is being achieved?”
Engineering the Complete System
Adiabatic cooling can provide significant additional cooling potential, but successful implementation requires the complete system to be considered.
Psychrometrics determine how much water can evaporate.
Hydraulics determine how that water can be delivered.
Atomization determines how effectively it interacts with the air.
Airflow determines how the droplets are transported.
And ultimately, the thermal behaviour of the Air-Cooled Heat Exchanger determines whether the reduction in inlet-air temperature creates meaningful process improvement.
That is why Fogging Web™ starts with the Air-Cooled Heat Exchanger itself.
Not with the nozzle.
Not with the pump.
Not with a predefined water flow.
But with the required cooling performance.
From Ambient Limitation to Measurable Cooling Improvement
When an Air-Cooled Heat Exchanger becomes a production constraint during high ambient conditions, the first step should always be to understand why.
Reduced airflow, bundle fouling, hot-air recirculation, mechanical degradation and insufficient installed surface can all contribute to poor performance.
Adiabatic cooling does not replace proper ACHE maintenance or performance diagnostics.
Instead, it provides an additional engineered option when the existing exchanger requires more cooling capacity during elevated ambient conditions.
By combining ACHE engineering, psychrometric analysis, high-pressure atomization, modular hardware and field performance verification, Fogging Web™ provides a practical route from ambient limitation to measurable performance improvement.
Engineered around the air cooler. Designed for performance.
Is your Air-Cooled Heat Exchanger limiting production during peak ambient conditions?
Enthalpex can evaluate the existing ACHE performance, quantify the potential benefit of adiabatic inlet-air cooling and engineer a Fogging Web™ configuration around the specific installation.
Measure. Analyse. Engineer. Verify.
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