Air-Cooled Heat Exchangers (Overview & Selection)

Air-Cooled Heat Exchangers (Overview & Selection)

What Is an Air‑Cooled Heat Exchanger (ACHE)?

An ACHE cools or condenses process fluids using ambient air as the heat sink. Extended‑surface finned tubes expand external area to offset the low air‑side film coefficient; a fan drives air across the bundle. ACHEs are widely used in refining, petrochemicals, power, pipelines and many other industries.

Air vs. Water Cooling — Pros & Cons

Air cooling saves water, avoids discharge/chemical treatment, reduces fouling and maintenance, and enables flexible siting. It has higher footprint and CAPEX, is sensitive to ambient dry‑bulb temperature, and noise control may be required. Water cooling is compact and can reach lower approach temperatures (near wet‑bulb), but consumes water, requires treatment, and adds corrosion/scaling risks.

Bundle Arrangements & Draft Types

Bundles may be horizontal, A‑frame (inclined/‘roof’), or vertical. Draft can be forced‑draft (fan pushes air upward through bundle) or induced‑draft (fan pulls air). Induced draft improves airflow uniformity and mitigates hot‑air recirculation; forced draft keeps drives out of the hot airstream and eases maintenance.

Cooling Modes: Dry, Wet, and Hybrid

Dry ACHE relies on sensible heat rise of air; outlet process temperature is limited by ambient dry‑bulb. Wet enhancement (humidification or spray) lowers inlet‑air temperature but adds water and fouling concerns. Hybrid (dry + wet) combines them to meet low outlet temperatures with reduced water use.

Finned‑Tube Options & Temperature Ranges

Common choices include L‑foot, LL‑foot, knurled KL, embedded G‑fin, and bi‑metal extruded/rolled fins (DR). G‑fin and DR types support higher temperature and durability; L/LL are economical for moderate duty. Oval and slotted/turbulator fins can boost heat transfer at the cost of higher pressure drop.

Fans, Drives, and Louvers

Axial fans with FRP or aluminum blades are typical; drive options include V‑belt, gear, or direct drive with VFD for turndown. Automatic pitch control and inlet louvers help match seasonal conditions and reduce power. Good ducting minimizes recirculation; guard/structure must consider vibration and noise.

Design & Selection Notes

Size for the site’s design ambient; check approach temperature limits and seasonal range. Account for air‑side pressure drop, fin fouling/cleaning, noise, drift (if wet), and access for maintenance. For very low outlet temperatures or cold climates, consider recirculation, louvers, or anti‑freeze measures.

Where ACHEs Fit Best

Ideal where water is scarce/expensive, discharge is constrained, or reliability and low OPEX are priorities. In many refineries and chemical plants, ACHEs have progressively replaced water coolers for these reasons.

AirsCooler Solutions

AirsCooler supplies OEM‑fit aftercoolers/intercoolers and custom ACHE bundles (L/LL/KL/G/DR fins) for revamps and new builds, including induced‑draft A‑frame units with VFD fans and low‑noise packages.