High Resolution Heat Transfer Measurements at the Three Phase Contact Line of a Moving Single Meniscus
In the present work the influences of contact line velocity and direction, as well as system pressure on the
local heat transfer characteristics in the vicinity of the three phase contact line are investigated experimentally.
The test facility provides a single liquid-vapour meniscus in a well-controlled saturated atmosphere. Carefully
degassed, thus pure fluorinert liquid PF-5060 is used as working fluid. The meniscus is positioned in a capillary
slot of 1.4 mm width between an isothermal polished copper wall on one side and a heater wall on the opposite
side. The heater wall consists of an infrared-transparent substrate coated with a thin metallic double-layer. This
allows well-controlled heat supply to the 2-phase fluid and accurate measurement of the temperature field
extremely close (approx. 800 nm) to the heater/fluid-interface using IR thermography with high spatial and
temporal resolution. From the 2-dimensional temperature fields, the local heat flux distribution is calculated. A
fluid displacement system enables a controlled movement of the meniscus in the capillary slot, thus simulating
advancing or receding contact line situations with controlled velocities. The presented results clearly show that and how the local heat transfer distribution depends on the contact line velocity and direction. In the situation
of an accelerated receding liquid/vapour-interface the moving meniscus leaves behind a thin liquid layer at the
wall, while it leaves behind a dry wall, when receding with a constant velocity. In the first case heat transfer
is dominated by thin film or microlayer evaporation, while in the second case it is governed by contact line
evaporation. These generic results can explain similar observations in different boiling regimes.