Abstract
In this paper experiments have been conducted to investigate the flow boiling and heat transfer characteristics in microchannels with three different surface wettability. Three types of microchannels with a super-hydrophilic surface (θ ≈ 0°), a hydrophilic surface (θ = 43°) and an untreated surface (θ = 70°) were prepared. The results show that the average heat transfer coefficient of a super-hydrophilic surface microchannel is significantly higher than that of an untreated surface microchannel, especially when the mass flux is high. The visualization of the flow patterns states that the number of bubble nucleation generated in the super-hydrophilic microchannel at the beginning of the flow boiling is significantly more than that in the untreated microchannel. Through detailed analysis of the experimental data, flow patterns and microchannel surface SEM images, it can be inferred that the super-hydrophilic surface microchannel has more active nucleation cavities, a high nucleation rate and a large nucleation number, a small bubble departure diameter and a fast departure frequency, thereby promoting the flow and heat transfer in the microchannel. In addition, through the force analysis of the vapor-liquid interface, the mechanism that the super-hydrophilic microchannel without dryout under high heat flux conditions is clarified.
Highlights
Two-phase flow boiling microchannels have appeared as one of the most efficient solutions for modern high heat flux cooling applications [1,2,3], including computer electronics, x-ray medical devices, satellite and spacecraft avionics and so on
More research is still required to understand the flow boiling enhanced heat transfer characteristics and mechanisms in super-hydrophilic microchannel compared with untreated microchannel, which is a main motivation for the present work, which emphasizes the effect of heat flux, inlet vapor quality and mass flux on the average heat transfer coefficients of aluminum-based microchannels of different surface wettability with
This paper is based on experimental research on the flow boiling heat transfer characteristics and mechanism of three types of microchannels with a super-hydrophilic surface (θ ≈ 0◦ ), a hydrophilic surface (θ = 43◦ ) and an untreated surface (θ = 70◦ )
Summary
Two-phase flow boiling microchannels have appeared as one of the most efficient solutions for modern high heat flux cooling applications [1,2,3], including computer electronics, x-ray medical devices, satellite and spacecraft avionics and so on. Flow visualization indicated local dryout occurring on the untreated surface at high heat flux and low mass flux, attached to deterioration in heat transfer performance. This tendency was not observed on a super-hydrophilic surface, which was consistent with recent research conclusions [13,14]. More research is still required to understand the flow boiling enhanced heat transfer characteristics and mechanisms in super-hydrophilic microchannel compared with untreated microchannel, which is a main motivation for the present work, which emphasizes the effect of heat flux, inlet vapor quality and mass flux on the average heat transfer coefficients of aluminum-based microchannels of different surface wettability with. The advantages and heat transfer mechanism of super-hydrophilic microchannel are further explored by utilizing flow visualization, in particular the reason of the bubble formation, avoiding dryout and the flow pattern transition
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