ISSN Online: 2377-424X
ISBN Print: 978-1-56700-474-8
ISBN Online: 978-1-56700-473-1
International Heat Transfer Conference 16
SUBCOOLED FLOW BOILING IN NARROW MICROCHANNEL UNDER DIFFERENT ORIENTATIONS AND SURFACE WETTABILITY CHARACTERISTICS
摘要
An experimental investigation of subcooled flow boiling in a high-aspect-ratio one-sided heating rectangular microchannel is conducted with hydrophilic and super-hydrophilic surfaces under different orientations utilizing deionized water as the working fluid. The super-hydrophilic surface is prepared through Plasma
Enhanced Chemical Vapor Deposition (PECVD). With the inlet fluid subcooling of 10°C, the mass fluxes are in the range of 200-500 kg/(m2s) while the heat fluxes vary from 4 W/cm2 to 25 W/cm2, and the orientation
angles are 0° (bottom-heated horizontal flow), 90° (vertical upflow), 180° (top-heated horizontal flow) and
270° (vertical downflow). An earlier occurrence of Critical Heat Flux (CHF) is presented for vertical downflow. With the direction of buoyancy opposite to the flow, the buoyancy impedes the departure and movement of bubbles against the inertia, causing easier bubble coalescence and elongation as well as partial dry-out process, which deteriorates heat transfer. At the mass flux of 200 kg/(m2s), the super-hydrophilic surface exhibits a delayed occurrence of CHF in the vertical orientation, while in the horizontal orientation it shows a heat transfer coefficient slightly higher by 10% for the bottom-heated flow as well as a heat transfer coefficient lower by 16% for the top-heated flow, compared with the untreated hydrophilic counterpart.