Capillarity effect on two-phase flow resistance in microchannels
Department of Mechanical, Industrial and Nuclear Engineering of the College of Engineering, Master's thesis, (October 2007)Abstract
Two-phase flow plays a major role in number of technologies used in fuel cells,
bioreactors, phase and particle separators, thermal management systems, chemical
reactors, etc. Some of these applications involve air–water two-phase flow in channels
much less than 1 mm in diameter. The fundamental understanding of flow characteristics,
such as flow regime, pressure drop, and heat transfer, is essential in the design and
control of these devices.
In this work, an experimental set-up is developed to investigate the effects of
surface energy/surface wettability and geometry on characteristics of two-phase flow in
horizontal microchannels at adiabatic conditions. Two-phase (air-water) slug flow is
established in microchannel test sections of varying sol-gel dip coated surface
wettabilities. Pressure drop measurements and flow pattern detection by high speed
visualization are employed to characterize the flow.
Results indicate that two-phase flow resistance is a strong function of surface
wettability and it increases with static contact angle. Significant change in contact line in
advancing and receding interface, and thus increase in flow resistance, is observed with
increase of hydrophobicity while geometry of the channels influences the frequency of
the slugs. Presence of thin liquid film, whose thickness is a strong function of wettability,
is observed experimentally which clearly elucidates the pressure drop variation with
surface wettability. Hence for characterizing two-phase flow in microchannels surface
wettability parameters should be accounted appropriately.