Abstract
Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly. A visual observation revealed that porous microchannels could suppress the flow fluctuation due to the establishment of a stable nucleate boiling process. Porous microchannels showed no advantage over the copper-based sample in the critical heat flux. The optimal thickness-to-particle-size ratio (δ/d) for the porous microchannel was confirmed to be between 2–5. In this range, the maximum enhanced effect on boiling heat transfer could be achieved.
Highlights
In order to meet higher cooling requirements, boiling heat transfer in microchannels has attracted increased attention in recent decades [1,2,3]
There are some fundamental problems which need to be answered: What is the potential the heat transfer capability of the porous microchannel? How do the particle size and particle shape affect the flow boiling process? What is the relationship between heat transfer performance (HTC and critical heat flux (CHF)) and flow fluctuation? In this work, we focus on investigating the overall characteristics of rectangle porous microchannels in detail to help resolve these issues
The boiling curves in different mass fluxes collapse into one line between 40.0–80.0 W/cm2, suggesting that the HTC in this range is only affected by heat flux
Summary
In order to meet higher cooling requirements, boiling heat transfer in microchannels has attracted increased attention in recent decades [1,2,3]. Some difficulties, such as flow instability, need to be overcome. Numerous studies [3,4,5,6] have shown that the bubble dynamics of boiling in microchannels are different from in the macro channel. The bubbles expand in the upstream direction and cause reversal flow problems due to the limitation of the narrow channel. In the forms of temperature and pressure fluctuations, have a negative impact on the heat transfer system. Porous structures have attracted increased attention due to their large quantity of nucleation sites as well as re-entrance cavities
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