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Flow measurement using micro-PIV and related temperature distributions within evaporating sessile drops of self-rewetting mixtures of 1-pentanol and water

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Original languageEnglish
Title of host publication4th Micro and Nano Flows Conference, University College London, 7th - 10th September 2014
Number of pages7
Publication statusPublished - 2014


Recently interest has arisen in the use of so-called self-rewetting mixtures for micro-scale heat
transfer systems. Such fluids, in which the surface tension can increase with increasing temperature, are
expected to offer superior evaporative cooling performance by extending the region of operation before dryout
of the heated surface sets in. Whilst improved performance has been shown in some practical situations
using these fluids, it is not entirely clear as to the mechanism of such improvements.
We have studied the flow within evaporating sessile drops of 1-pentanol-water mixtures using micro-PIV
and have observed three stages in the evaporation process. During the first stage there appears to be a single
toroidal vortex with flow inwards along the base of the drop. The vortex only occupies the central region of
the drop and appears to pulsate, reducing in size during evaporation. This is followed by a second transition
stage to a third stage in which the flow is directed radially outward, as observed by us for pure water droplet
evaporation and in the latter stages of ethanol/water drop evaporation. Temperature measurements, using IR
thermography suggest that the initial stage of evaporation may be controlled by thermal Marangoni effects as
opposed to the concentration driven Marangoni flows postulated for ethanol-water mixtures.

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