High-performance thermal management devices require both high heat flux and high heat transfer coefficient (HTC). Boiling heat transfer provides an effective way toward these goals by utilizing the large latent heat of vaporization. However, HTC of typical pool boiling is hindered by thick liquid layer with relatively slow bubble dynamics. We recently demonstrated a “thin film boiling” mechanism that significantly increases both the critical heat flux and HTC of boiling, when the liquid film is thinner than the thermal boundary layer. In this work, we further explore the “thin film boiling” regime by controllably confining the liquid water film within a narrow gap between the heater wall and a hydrophobic vapor-permeable membrane. We systematically vary the gap thickness from 1.7 mm to 190 μm and demonstrate an obvious reduction in the liquid-vapor phase change resistance by reducing the liquid layer thickness. With smaller gaps, we find a decreasing trend in the effective superheat of the thin film boiling, reaching as low as 3.5 ± 0.3 K at heat flux of 133.8 ± 7.7 W cm⁻², where the effective superheat is the difference between the heater wall temperature and the saturation temperature of the liquid in the gap and represents the liquid-vapor phase change resistance only, excluding the vapor flow resistance from the liquid-vapor interface to the far field. The ultralow effective superheat leads to a high HTC associated with the phase change process of 38.4 ± 1.0 W cm⁻² K⁻¹ in the 190 μm gap. We further show that there is a transition from the thin film boiling to evaporation regime when liquid water recedes into the nanopores of the porous heating membrane. The HTC at these transition points can be well captured by the Hertz-Knudsen (H-K) relationship with an accommodation coefficient of ~0.16, which also demonstrate that the phase change process at these transition points are close to the kinetic limit.

高性能热管理设备需要高热通量和高热传递系数（HTC）。沸腾传热通过利用大量的汽化潜热为实现这些目标提供了有效的途径。然而，典型的池沸腾的HTC受具有较慢气泡动力学的浓液体层的阻碍。我们最近展示了一种“薄膜沸腾”机制，当液膜比热边界层薄时，该机制可显着提高临界热通量和沸腾HTC。在这项工作中，我们通过可控地将液态水膜限制在加热器壁和疏水性透湿膜之间的狭窄间隙中，进一步探索“薄膜沸腾”状态。我们系统地将间隙厚度从1。在7mm至190μm的范围内，并且通过减小液体层的厚度证明了液体-蒸汽相变阻力的明显降低。在较小的间隙下，我们发现薄膜沸腾的有效过热度呈下降趋势，在133.8±7.7 W cm的热通量下可降至3.5±0.3 K^－2，其中有效过热是加热器壁温和间隙中液体的饱和温度之间的差，并且仅代表液体蒸气相变阻力，不包括从液体蒸气界面到远处的蒸气流动阻力领域。超低的有效过热导致与38.4±1.0 W cm ^-2  K ^-1的相变过程相关的高HTC在190μm的间隙中。我们进一步表明，当液态水退回到多孔加热膜的纳米孔中时，从薄膜沸腾过渡到蒸发状态。这些转变点的HTC可以通过Hertz-Knudsen（HK）关系很好地捕获，适应系数约为0.16，这也表明这些转变点的相变过程接近动力学极限。