TY - JOUR
T1 - Boiling flow characteristics in microchannels with very hydrophobic surface to super-hydrophilic surface
AU - Liu, Ting Y.
AU - Li, P. L.
AU - Liu, C. W.
AU - Gau, C.
N1 - Funding Information:
This research is sponsored by National Science Council of Taiwan under contact no. NSC 97-2221-E-006-057 -MY2 .
PY - 2011/1/15
Y1 - 2011/1/15
N2 - Boiling flow process plays a very important role to affect the heat transfer in a microchannel. Different boiling flow modes have been found in the past which leads to different oscillations in temperatures and pressures. However, a very important issue, i.e. the surface wettability effects on the boiling flow modes, has never been discussed. The current experiments fabricated three different microchannels with identical sizes at 105 × 1000 × 30000 μm but at different wettability. The microchannels were made by plasma etching a trench on a silicon wafer. The surface made by the plasma etch process is hydrophilic and has a contact angle of 36° when measured by dipping a water droplet on the surface. The surface can be made hydrophobic by coating a thin layer of low surface energy material and has a contact angle of 103° after the coating. In addition, a vapor-liquid-solid growth process was adopted to grow nanowire arrays on the wafer so that the surface becomes super-hydrophilic with a contact angle close to 0°. Different boiling flow patterns on a surface with different wettability were found, which leads to large difference in temperature oscillations. Periodic oscillation in temperatures was not found in both the hydrophobic and the super-hydrophilic surface. During the experiments, the heat flux imposed on the wall varies from 230 to 354.9 kW/m2 and the flow of mass flux into the channel from 50 to 583 kg/m2s. Detailed flow regimes in terms of heat flux versus mass flux are also obtained.
AB - Boiling flow process plays a very important role to affect the heat transfer in a microchannel. Different boiling flow modes have been found in the past which leads to different oscillations in temperatures and pressures. However, a very important issue, i.e. the surface wettability effects on the boiling flow modes, has never been discussed. The current experiments fabricated three different microchannels with identical sizes at 105 × 1000 × 30000 μm but at different wettability. The microchannels were made by plasma etching a trench on a silicon wafer. The surface made by the plasma etch process is hydrophilic and has a contact angle of 36° when measured by dipping a water droplet on the surface. The surface can be made hydrophobic by coating a thin layer of low surface energy material and has a contact angle of 103° after the coating. In addition, a vapor-liquid-solid growth process was adopted to grow nanowire arrays on the wafer so that the surface becomes super-hydrophilic with a contact angle close to 0°. Different boiling flow patterns on a surface with different wettability were found, which leads to large difference in temperature oscillations. Periodic oscillation in temperatures was not found in both the hydrophobic and the super-hydrophilic surface. During the experiments, the heat flux imposed on the wall varies from 230 to 354.9 kW/m2 and the flow of mass flux into the channel from 50 to 583 kg/m2s. Detailed flow regimes in terms of heat flux versus mass flux are also obtained.
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U2 - 10.1016/j.ijheatmasstransfer.2010.09.060
DO - 10.1016/j.ijheatmasstransfer.2010.09.060
M3 - Article
AN - SCOPUS:78449305488
SN - 0017-9310
VL - 54
SP - 126
EP - 134
JO - International Journal of Heat and Mass Transfer
JF - International Journal of Heat and Mass Transfer
IS - 1-3
ER -