Due to its outstanding heat transfer performance, flow boiling has a wide range of applications in many fields, especially for cooling of electronic devices. Previous studies have shown that the liquid replenishment on the downstream of the heating surface is the critical restriction of the increase of the critical heat flux (CHF). In this work, we designed a series of heterogeneous surfaces with fractal treelike hydrophilic networks for flow boiling enhancement. The micro-pin-finned surface structures are expected to increase the CHF and reduce the superheat by its high wickability. Moreover, by virtue of the efficient transport capacity of treelike networks, the fractal hydrophilic paths are designed to serve as the liquid delivery channels for the liquid replenishment on the downstream of the heating surface. The heterogeneous surfaces improve the comprehensive boiling heat transfer performance, especially the CHF, which is 82.2% higher than that of the smooth surface and 5.4% higher than the surface homogeneously covered by the microstructure with twice of the extended surface area. This work provides reference for the design of heterogeneous surfaces with both smooth and structured parts to increase the flow boiling CHF to some extent.
Keywords: boiling; bubble behavior; critical heat flux; fractal; heat transfer coefficient.