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Description of Driving Event:

A uniquely designed external ram air exchanger has been analyzed and performance tested at the NASA Langley Research Center. The heat exchanger is attached externally to an aircraft and is used to cool a laser system within the fuselage. In the limited space available, with a conventional staggered tube array, estimates showed insufficient cooling capacity. Thus, a non-conventional design was developed with larger tube and fin area exposed to the ram air to increase the heat transfer performance. The basic design consists of 28 circular finned aluminum tubes arranged in two parallel banks. Wind tunnel tests were performed to simulate air and liquid flight conditions for both the non-conventional parallel bank arrangement as well as the conventional staggered tube arrangement. Test results are used in a computer model of the heat exchanger to predict the operating performance for the entire flight profile. These analyses predict significantly improved performance over the conventional design and show adequate thermal control margins.

Aircraft-borne experiments requiring large electrical power loads create a significant challenge to provide efficient thermal control for a variety of flight environments. Heat dissipation by convection within the aircraft is often limited, so the thermal load must be dumped overboard using an external heat exchanger. Due to aerodynamic restrictions, the allowable heat exchanger area outside the aircraft is usually extremely small. Thus, a heat exchanger with a small frontal area must be designed to meet the stringent thermal requirements of the experiment.

For a thorough discussion of this heat exchanger see paper #902019, SAE technical paper series, "Thermal Control of a LIDAR Laser System Using a Non-Conventional Ram Air Heat Exchanger", by Brian D. Killough, William Alexander, Jr., and Doyle P. Swofford, all of the NASA Langley Research Center, Hampton, Virginia 23665