Exchanger in which ambient air is the cold fluid, driven by axial fans over a finned tube bundle (to compensate for air's low convective coefficient). Removes cooling-water demand — a decisive argument in arid regions or under environmental restriction. Designed to API 661.
Configurations
- Forced draft — fan below, pushes air through the bundle; standard.
- Induced draft — fan above, pulls air; better distribution, less recirculation.
- Wet-fin / humidifying — upstream misting to reduce dry-bulb temperature during heat peaks.
Reliability: fan imbalance and bearing wear (dominant), fin fouling/deposits (drastically reduces U), tube corrosion, header joint integrity. One of the few pieces of equipment whose most critical failure mode is not in the process fluid but in the auxiliary air machine.