Investigation Of Heat Transfer Enhancement By Modulation Of Boiling Bubble Dynamics By Deaeration Board

As a high-efficiency heat transfer mode,boiling is a widely used in highefficiency heat exchanger,high heat density electronics cooling and the temperature control system of aerospace,The structure of an additional "Deaeration Board(DB)"with various heat transfer surfaces is used in this paper to investigate the impact of a deaeration board on boiling bubble and boiling heat transfer performance using the physical foundation of boiling bubble dynamics.Firstly,a single bubble boiling experiment is carried out on a monocrystalline silicon surface.DBs with different hydrophobicity were prepared and suspended over the monocrystalline silicon surfaces to record and observe the bubble dynamics using high-speed camera.The evolution of boiling bubbles during the growth and departure stages was monitored systematically.The results show that both the height and wettability of DB have important effects on the dynamic characteristics of boiling.When the height is less than the maximum growth height,the "DB" forces the bubble departure and reduces the maximum bubble departure diameter.When the contact angle of "DB " is 150°,the deaeration effect is the best,and the bubble departure stage can be shortened into 3 ms,and the instantaneous deaeration rate can reach 5.46 mm3/ms,which is 3.96 times that on the surface with the wetting contact angle at 100°.Coupling controlling the height,the wettability and the boiling surface can realize an external intervention in the growth stage and promoting the bubble departure.Correspondingly,the whole process of boiling dynamics can be modified.Secondly,an experimental rig for saturated pool boiling testing heat transfer performance in pools was built to discover the modulation of the DB on saturated pools with smooth surfaces and copper foam surfaces.The experimental results indicate that in the low and medium heat flow density regions the saturated boiling was enhanced by the DB.When q≈16.09 W/cm2 in the low heat flow density region,the heat transfer performance of smooth surface is increased by 20%,and that of the copper foam surface is increased by 21%when q≈0.8 W/cm2.The lower height of DB will restrict its enhancement performance in the medium heat flow density,but this weakness can be avoided by properly adjusting the height of DB.Due to the roughness of the smooth surface on its nucleation sites and the lower height of DB,the enhanced modulation of the smooth surface by the DB is limited.When q≈32.7 W/cm2 and h0=2.83 mm,the heat transfer effect is weakened to some extent by the continuous air film formed between the DB and the smooth surface.As the height of the DB is increased to h=6.06 mm,the boiling heat transfer coefficient increases to about 6.25%compared to the condition without the DB.In addition,the copper foam surface can provide more nucleation sites,and when q≈35.2 W/cm2,the boiling heat transfer coefficient of modulated copper foam surface is enhanced by about 16.11%with the height of DB increased from h0=3.89 mm to h=6.32 mm.Meanwhile,using an "air-suck needle" structure is supposed to have a stronger enhancement effect in high heat flow density.