Pool boiling of water on micro-nanostructured oil-impregnated surfaces

• Bubbles are accompanied by an annular wetting ridge on oil-impregnated surfaces • The wetting ridge delays bubble coalescence and departure • Oil-impregnated surfaces have larger bubble departure diameters • Oil-impregnated surfaces have longer bubble residence time • Oil-impregnated surfaces have comparable CHF to their counterpart without oil Boiling can effectively remove concentrated heat from electronic devices due to the large latent heat of phase change. The heat removal rate greatly depends on the bubble-surface interaction. In this study, we investigated the bubble dynamics and boiling heat transfer performance of hemi-solid hemi-liquid surfaces that are created by impregnating micro-nanostructured surfaces with oil. These surfaces exhibit record-low contact angle hysteresis (1–2°), providing bubbles with high mobility. Pool boiling of water on these surfaces, along with rigid surfaces with different wettability, was tested. High-speed images show that the average bubble departure diameter on oil-impregnated surfaces was ≈60% larger and the average bubble residence time was ≈70% longer compared to their counterparts without lubricant. We attribute this result to the wetting ridge, which increases the downward forces on departing bubbles and creates a physical barrier for bubble coalescence. The wetting ridge naturally forms when bubbles nucleate on oil-impregnated surfaces due to the unbalanced vertical component of interfacial forces. To provide insight into boiling heat transfer, we experimentally measured the critical heat flux (CHF), the maximum heat flux achievable before the boiling crisis. The CHF on oil-impregnated surfaces was ≈28-36 W/cm², comparable to that of the counterpart surface without oil (≈27 W/cm²). We attribute this result to oil depletion, which rendered the textured oil-impregnated surfaces superhydrophobic, as confirmed by surface analysis after boiling. In addition to experimentally measuring boiling heat transfer performance, this work provides new insight into bubble growth and departure mechanisms on textured oil-impregnated hemi-solid hemi-liquid surfaces.