Direct local heat flux measurement during water flow boiling in a rectangular minichannel using a MEMS heat flux sensor

Heat transfer characteristics of water flow boiling in a minichannel were investigated through the direct measurement of local heat flux using a fabricated MEMS heat flux sensor with a multi-layered structure. Local temperatures and heat fluxes in the water flow boiling were measured at a sampling frequency of 10 kHz in synchronism with the high-speed visualization of the boiling behavior. The measurement results revealed fundamental heat transfer processes, including thin liquid film evaporation, dry-out of the liquid film, transient heat conduction after dry patch rewetting, and single-phase forced convection. The thin liquid film evaporation indicated a high local heat flux that was well over 1 MW/m(2) and provided a dominant contribution to the wall heat transfer. Furthermore, the post-rewetting transient heat conduction indicated a high heat flux that was higher than 1 MW/m(2). However, it was insignificant in terms of the overall wall heat transfer at all the tested heat fluxes because of its short duration. The contribution of liquid-phase forced convection was also small, except at low vapor qualities.

Automated summary

The study found that in water flow boiling in a minichannel, thin liquid film evaporation provides a high local heat flux and dominates wall heat transfer; post-rewetting transient heat conduction, though having high heat flux, has minimal overall impact on wall heat transfer; liquid-phase forced convection contributes little, especially at low vapor qualities.