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Film Temperature And Thickness Measurements Of An Impinging Oil Jet For Cooling Of Electric Components Based On Two-Color Laser-Induced Fluorescence.

Matthias Koegl, Nikita Mil’to, Lars Zigan

Universität der Bundeswehr München Institut für Thermodynamik (LRT-10), Neubiberg, Germany


A fluorescence based two-color detection scheme is used to characterize a jet impingement cooling process relevant for electric and electronic applications. The presented technique enables a simultaneous determination of film temperature and film thickness. The fluorescence signal was generated by the temperature-sensitive fluorescence tracer nile red, which was added to Marlotherm LH, a commercially available heat transfer oil. Suitable band pass filters enable accurate temperature measurements. A preliminary spectral study investigates the influence of dye concentration, temperature and film thickness. At high dye concentrations (up to 37.5 mg/L) reabsorption effects takes place and lead to a spectral shift towards higher wavelengths with increasing film thickness. Low dye concentrations (0.59 mg/L) exhibit no film thickness dependent spectral shift. A film temperature investigation at low dye concentration showed no bias of the intensity ratio due to film thickness, i.e. no additional spectral shift towards lower wavelengths was observed. The investigations on the jet impingement setup revealed an increasing film temperature and decreasing film thickness with increasing solid temperature. The average film temperature increases with increasing solid temperature from 298 K (solid temperature 298 K) to 308 K (solid temperature 398 K). At higher solid temperatures, the film temperature increases with distance to the stagnation zone. The average film thickness decreases with increasing solid temperature from 0.24 mm to 0.17 mm. At high solid temperatures, the film temperature increased with radial distance to the stagnation zone. This behavior is caused by the increasing temperature gradient with increasing solid temperature and decreasing viscosity with increasing film temperature.

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