LIF-thermometry with MDR-enhanced energy transfer for micro-droplet temperature imaging for varying ambient pressures
Leif Schumacher  1, *@  , Johannes Palmer  1@  , Valeri Kirsch  2@  , Manuel A. Reddemann  1@  , Reinhold Kneer  1@  
1 : Institute of Heat and Mass Transfer, RWTH Aachen University
Augustinerbach 6, 52062 Aachen -  Germany
2 : Institute of Heat and Mass Transfer, RWTH Aachen University
Augustinerbach 6, 52062 Aachen -  Germany
* : Corresponding author

A relatively new method called pulsed 2D-2cLIF-EET is applied for temperature imaging of heated micro droplets.
The method uses laser induced fluorescence to determine the local temperature field in droplets. Due to the application
of a pulsed laser the planar imaging of moving droplets is not restricted to motion blur anymore. Enhanced
energy transfer is used to prevent dye-lasing and makes LIF thermometry possible even with high excitation energies
of pulsed lasers. The system offers an average droplet temperature accuracy of 0.5 K and a spatial median
absolute deviation of approximately 2.5 K. The local temperature values of every pixel represent an integral temperature
along the droplet depth. Thus, the three dimensional temperature field is averaged and projected onto two
dimensions (planar). The system is used to measure the planar temperature field of a n-dodecane droplet stream
in hot gas atmosphere. Experiments are conducted with ambient pressures of 1.39 bar and 2.11 bar. The raising
ambient pressure influences the convective heat transfer at the droplet surface (increased by around 15%) and
thereby heat transfer into the droplet. The temperature distribution inside the droplet does not show the typical
structure of a Hill-vortex, which would be characteristic for the flow inside a moving droplet. Comparison with the
"effective thermal conductivity model" for a monodisperse droplet stream shows good agreement for the low ambient
pressure, but deviations for the elevated pressure.

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