Air Cooler Testing at HTRI

HTRI is installing an industrial-scale ACHE this year to improve airflow predictions and enhance testing flexibility.

Salem Bouhairie, Senior Project Engineer, Research
February 8, 2017

HTRI’s air-cooled heat exchanger (ACHE) studies are a fundamental part of our research program. The most pressing concern expressed by our members about airside cooling involves low airflow predictions under forced and natural draft operations. To more fully address this concern, our future studies will include approach velocity, wind, ground clearance, and obstruction effects.

HTRI has taken a bidirectional approach in advancing air-cooler testing: physical experiments and computational fluid dynamics (CFD). In 2016, HTRI conducted CFD simulations of forced-draft air-cooled heat exchangers to examine hot air recirculation problems (as reported in The Exchanger), as well as other issues that would help us design this test unit. From these initial CFD studies (see figure), we have designed our first “real” ACHE since the 1970s.

In 2017, we are installing the actual industrial-scale air cooler at the HTRI Research & Technology Center (RTC). This research unit, designed according to practical API 661 [1] guidelines, incorporates two fan cells. Unlike conventional production-type air coolers, this test unit also features a fixed tube bundle layout with the option of forced-draft or induced-draft plenums. To record airside measurements, a traverse system holds various anemometers, thermocouples, and temperature loggers, as well as static and total pressure sensors.

The test unit also features

  • a 1.8-m (6-ft) wide bundle with six rows of 4.9-m (16-ft) long tubes
  • extruded fin tubes (stainless steel tubes to avoid corrosion and contact resistance with fin joint, with aluminum fins to enhance thermal conductivity)
  • chimneys for natural draft operation
  • manual louvers to control air flow and temperature
  • a variable frequency drive (VFD)
  • variable ground clearance
  • obstacles beside and under the air cooler

This air cooler is designed to operate with a maximum duty of 4.7 MW (16 MMBtu/hr). Initial tests will use water cooling and steam condensing services. In the future, this HTRI unit offers flexibility for testing and addressing other field operation concerns.

Contact HTRI at for more information.


  1. API STD 661: Petroleum, Petrochemical, and Natural Gas Industries—Air-cooled Heat Exchangers, 7th ed., American Petroleum Institute, Washington, DC (2013).
Figure 1. Initial CFD model of forced-draft air cooler operating in a cross wind