Microbubble nucleation from an artificial cavity in single microchannel

초록

Bubble nucleation of flow boiling from a single artificial cavity has been visualized in a microchannel. Visualization uses 4 ns pulse light at 532 nm wavelength from two resonance Nd:YAG lasers for the illumination. And in order to take two sequential images, a progressive scan digital CCD camera with straddling techniqueat 50,000 frame per second. An integrated MEMS device is fabricated for the investigation. The device is composed with a single microchannel (Dh = 67 um), a single artificial cavity (Radius of cavity (Rc) = 15um) (a), visualization window, Pt-line heater for constant heat flux condition, and Pt-RTD temperature sensors on both sides. The visualized sequential images (b) are applied to map the bubble growth (c). The map (c) shows that the bubble growth rate is quite linear ((b), A-I) until the bubble forms as an annular flow ((b), K and L). (d) schematically show the difference in the flow regime development between meso and micro-scale flow boiling. A single bubble from a cavity explosive grows and fills whole downstream of channel without coalescence and confinement with other bubbles ((b), K and L)