Boiling regimes in uncoated polydimethylsiloxane microchannels with a fine wire heater

Polydimethylsiloxane (PDMS) is a type of gas permeable media widely used in microfluidic applications. In this work multiphase patterns and boiling curves in PDMS square microchannels were experimentally investigated. Very fine platinum wires with diameter of 50 μm were embedded through the microchannels and serving as heater. The multiphase patterns were visualized by means of high speed CCD camera with microscope. Curves of temperature versus heat flux on the wire heaters were plotted. Based on the evolution of multiphase patterns, five boiling regimes were classified, that is, single phase, bubble formation, slug formation, slug dominated and dry out. Interestingly, the bubbles were generated from the channel walls rather than the heater surface, and so-called “droplets-in-bubble” phenomenon drew attention in which bunches of microdroplets kept forming, growing, and disappearing within the big bubbles. The boiling curves were plotted and compared to boiling in open space and in glass tubes. The heat transfer in the PDMS microchannels got deteriorated when the bubbles formed.