Pool boiling heat transfer of porous structures with reentrant cavities

• Porous structures with Ω-shaped reentrant cavities (PS–RC) are developed.
• Pool boiling heat transfer enhancement is accessed for PS–RC.
• Pool boiling heat transfer mechanisms of PS–RC are identified.

Porous structures with reentrant cavities (PS–RC) were proposed and developed for pool boiling cooling systems. They were totally constructed by sintered copper powder via a solid-state sintering method. They featured 12 parallel Ω-shaped reentrant channels with large circular cavities inside and narrow exit slots upside. Their pool boiling heat transfer performance was systematically explored using two coolants (deionized water and ethanol) in different liquid subcoolings (3–30 °C) at atmospheric pressure. Solid structures with the same reentrant cavities were prepared and tested for comparison. Experimental results revealed that the porous structures with reentrant cavities presented a significant reduction of wall superheat for the onset of nucleate boiling (ONB), and a maximum 3 and 5.3 folds enhancement in pool boiling heat transfer in water and ethanol tests, respectively. The above enhancement was associated with the merits of PS–RC in the enlargement of heat transfer area, increase in active nucleation sites and improvement of liquid replenishment. Besides, the heat transfer curves together with visualization results showed that three boiling regimes dominated in the PS–RC with the increase in heat fluxes, i.e., isolated bubbles nucleate boiling, fully developed nucleate boiling and bubbles coalescence nucleate boiling. The PS–RC was able to maintain sufficient liquid replenishment and efficient surface rewetting even at high heat fluxes, which help to avoid the fast deterioration of heat transfer at moderate to high heat fluxes.