ARTICLE:

• A NEW TECHNIQUE FOR MEASUREMENTS OF UNSTEADY HEAT TRANSFER TO AIR USING A THIN METALLIC-FOIL AND INFRARED THERMOGRAPHY  download article

H. Nakamura
Department of Mechanical Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka, Kanagawa, 239-8686, Japan

T. Igarashi
Department of Mechanical Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka, Kanagawa, 239-8686, Japan

ABSTRACT

A new technique for measurements of time-space characteristics of heat transfer to air has been developed using infrared thermography. A thin metallic-foil with a low heat capacity was used as a test surface, which was heated by applying a direct current. In this work, the frequency response of the test surface was investigated by solving the heat conduction equations by considering the heat losses. Also, the spatial resolution of the test surface due to lateral conduction was investigated. In order to verify the applicability of this measurement technique to practical measurements, unsteady heat transfer on the wall of a turbulent boundary layer was measured. An extremely thin metallic-foil − 0.15-μm thick platinum leaf − was employed as the test surface in order to improve both the frequency response and the spatial resolution. The time-space distribution of the heat transfer coefficient was calculated from a series of instantaneous temperature distributions measured using infrared thermography and by considering the delay due to the heat capacity of the foil and lateral conduction through the foil. Consequently, the unsteady behaviour of the heat transfer was clearly visualized, which was caused by streaks formed in the near-wall region.

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