Analysis of flow patterns emerging during evaporation in parallel
microchannels
International Journal of Heat and Mass Transfer, 50 (1-2):
226-239 (2007)Abstract
The evaporation processes of 2-propanol and water in cyclo olefin
polymer (COP) and silicon microchannels of square cross-section are
studied with a high-speed camera. The COP channels with a cross-section
of 50 mum x 50 mum are rather smooth, whereas the 30 mum x
30 mum silicon channels have comparatively rough surfaces. For
the COP channels, two different evaporation modes are identified,
both with oscillating liquid-vapor menisci. One of these modes is
characterized by an extremely rapid evaporation and a corresponding
discontinuous shift of the meniscus. In the silicon channels four
different evaporation modes are observed. Oscillatory motion of the
liquid fronts also dominates here, and depending on the total mass
flow and the wall temperature the oscillations in different channels
are synchronized or desynchronized. Besides the flow patterns also
the velocity trajectories of the evaporating liquid fronts are analyzed
in detail and show a rather good reproducibility over different channels
and different cycles. Compared to most other studies reported in
this field, bubble nucleation is found to be of secondary importance
for the evaporation processes.