Experimental StudyHigh Altitude Forced Convective Cooling of Electromechanical Actuation Systems
Technical Report,07 Feb 2014,31 Dec 2015
University of Dayton Research Institute Dayton United States
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The evaluation of the effects of altitude on forced air convective cooling is studied experimentally. The evolution of the more electric aircraft has led to the adoption of high power electronics for flight critical systems and the need to mitigate their thermal loads. Changes in altitude affect properties that govern heat transfer, such as air pressure, density, and temperature. Current methodology behind heat transfer prediction lacks a comprehensive experimental validation at altitudes above 16,000 feet, relevant to commercial and military aircraft. The convective heat transfer coefficient at altitudes from 0 to 52,000 feet above sea level at sea level room temperature 24 C was measured through the use of a wind tunnel inside a vacuum chamber. Test results, with Reynolds number ranging from 500 to 14,000 and pressure from 0.1 atm to 1.0 atm, confirm that the Nusselt number and pressure loss coefficient are independent of altitude and can be determined from experimental measurement, numerical simulation, and suitable correlations obtained at sea level. Both quantities are functions of Reynolds number only. This experimental investigation will serve to provide a greater confidence for predictive methods of heat transfer at high altitude, which can lead to better optimized thermal management solutions for flight control electromechanical actuation systems.