An experimental study of the heater size effect on micro boiling is reported in detail. Using 1.6-ms-wide and 40-μs-wide heating pulse, boiling in subcooled water is investigated on thin film Platinum heaters with various feature sizes ranging from 1μm to 10μm. Two groups of boiling patterns generated by a set of different sizes of micro bubble actuators are observed using stroboscopic video microscopy. Below the critical heater size, single spherical bubble is observed (Group I); while the other case, bubble collapse as an oblate vapor film (Group II). The critical heater size for different heating pulse width is summarized by normalizing heater size with diffusion length of the heating pulse width....[ Read more ]

An experimental study of the heater size effect on micro boiling is reported in detail. Using 1.6-ms-wide and 40-μs-wide heating pulse, boiling in subcooled water is investigated on thin film Platinum heaters with various feature sizes ranging from 1μm to 10μm. Two groups of boiling patterns generated by a set of different sizes of micro bubble actuators are observed using stroboscopic video microscopy. Below the critical heater size, single spherical bubble is observed (Group I); while the other case, bubble collapse as an oblate vapor film (Group II). The critical heater size for different heating pulse width is summarized by normalizing heater size with diffusion length of the heating pulse width.

The polysilicon micro/nano bubble actuators, integrated with self-sensing temperature microsensors, are fabricated to study the size effect in nano scale. Based on a capped trimming hard-mask (CTHM) method, nano bubble actuators with smallest width 0.1 μm have been successfully fabricated using the 0.5 μm lithography equipments. Similar bubble dynamics and size effect of boiling pattern are visualized by the same stroboscopic video microscopy. The results in platinum micro bubble actuators are quite consistent with the polysilicon’s counterpart. Size effects in bubble lifetime, bubble size and bubble shape are discussed.

Minimum power for bubble onset and its average temperature on micro/nano bubble actuators are measured by using the self-sensing temperature senor. Most bubble actuators have temperature above the superheat limit (300°C), which indicates the homogeneous nucleation. Size effect on onset power flux and its temperature is observed discussed.