Annals of the Assembly for International Heat Transfer Conference 13

ISBN 1-56700-225-0 / CD 1-56700-226-9

Year 2006

H. Herwig
Technische Thermodynamik, TU Hamburg-Harburg, 21073 Hamburg, Germany

H. Mocikat
Hamburg University of Technology, Hamburg, Germany

A double layer hot film with two 10 μm nickel foils, separated by a 25 μm Polyimide foil is used as a multi-purpose sensor. Each foil can be operated as a (calibrated) temperature sensor in its passive mode by imposing an electric current small enough to avoid heating by dissipation of electrical energy. Alternatively, however, each foil can also serve as a heater in an active mode with electric currents high enough to cause Joule heating.
This double foil sensor can be used as a conventional heat flux sensor in its passive mode when mounted on an externally heated surface. Together with the wall and free stream temperature this measured heat flux will provide the local heat transfer coefficient h = q_w/(T_w − T_∞). In fully turbulent flows it alternatively can be operated in an active mode on a cold, i.e. not externally heated surface. Then, by heating the upper foil, a local heat transfer is initiated from which the local heat transfer coefficient h can be determined, once the lower foil is heated to the same temperature as the upper one, thus acting as a counter-heater. The overall concept behind this mode of measurement is based on the local character of heat transfer in fully turbulent flows, which turns out to be almost independent of the upstream thermal events.

EXP-05 pages DOI: 10.1615/IHTC13.p21.50 Download article

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