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Air-Cooled Heat Exchanger (Fin-Fan) Calculator mechanical
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Air-Cooled Heat Exchanger (Fin-Fan) Calculator

Size industrial Fin-Fan air-cooled heat exchangers (ACHE) to determine required bare and finned tube surface areas, fan airflow in ACFM, and face velocities per API 661.

Process Duty & Temperatures

Typically 20°F to 35°F for API 661 fin-fan coolers

Tube Bundle Geometry & Sizing

BTU / (hr·ft²·°F) bare tube reference

Airflow & Fin Surface Sizing

Total Required Cooling Airflow
-- ACFM
-- Fan Motor Horsepower
Face Air Velocity
-- FPM
API 661 compliant
Extended Fin Area
-- sq ft
-- sq ft bare tube
Effective MTD (Crossflow): -- °F
Bundle Face Area: -- sq ft
Exit Air Temperature: -- °F
API 661 recommends air face velocities between 450 to 650 FPM across the tube bundle face to prevent fan stall and excessive acoustic noise.

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Tested hardware and components for high reliability

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Frequently Asked Questions

Why are extended aluminum fins used on air-cooled heat exchangers?

Air has a very low thermal conductivity and convection coefficient compared to liquids (h_air ~ 5 to 10 BTU/hr·ft²·°F vs h_water ~ 800 to 1,500). By wrapping high-density aluminum fins around the tubes, the external heat transfer area is increased by 15 to 22 times, equalizing the air-side and tube-side thermal resistances.

What is the difference between forced draft and induced draft Fin-Fan coolers?

In forced draft units, fans are mounted below the tube bundle and push ambient air upward across the tubes, providing easy ground-level motor maintenance. In induced draft units, fans are mounted above the bundle and pull air through, providing superior air distribution and shielding the bundle from solar radiation, rain, and hot-air recirculation.

What are the API 661 air face velocity limits?

API Standard 661 (Petroleum and Natural Gas Industries - Air-Cooled Heat Exchangers) recommends face velocities between 450 and 650 FPM. Lower velocities lead to inefficient bay utilization and low air-side heat transfer, while higher velocities cause turbulent fan blade stall and blade-pass acoustic noise.