Three types of microchannel surface (TS#1

TS#2

and TS#3) with non-uniform wettability were fabricated on bare copper surfaces by surface modification technology and electrical discharge machining (EDM). Each microchannel had the same rectangular cross section with a depth of 800 μm and width of 600 μm. The width of fin between two successive microchannels was also 600 μm. All these three microchannel surfaces had the same contact angle of 113.2° for the sidewall and bottom surfaces

but for the top surfaces

the contact angles were 8.6°(TS#1)

88.1°(TS#2) and 156.1°(TS#3)

respectively. During the EDM fabrication process

cavities of 10 μm in size was formed due to the electric sparking. Thus

the fabricated microchannel surfaces were multiscale surfaces. The statured pool boiling heat transfer characteristics of deionized water on these three types of microchannel surface as well as the bare copper surface were investigated experimentally. Compared with the bare copper surface (BS

θ=88.6°)

all these three microchannel surface with non-uniform wettability manifested a better heat transfer performance. The critical heat fluxes for TS#1 and TS#3 were increased by 61% and 35% compared with BS

while the maximum heat transfer coefficients were increased by 2.3 and 6 times. The bubble dynamics on the heated microchannel surfaces was visualized with a high speed camera. It was found that the surface property of non-uniform wettability can postpone bubble column coalescence

thus the gaps among bubble columns can provide the effective routes for the liquid supplementary to the heated surface

avoiding the occurrence of dry-out and enhancing the critical heat flux.