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• The smooth surface's CHF enhancement by electric field ranges from 15.2% to 22.5%. • Microstructured surfaces' CHF increment by electric field ranges from −3.9% to 19.2%. • The CHF of PF50-60 is decreased by the electric field at ΔTsub = 25 and 35 K. • The increase of CHF by electric field is closely related to the field trap effect. The uniform electric field is an effective method to improve boiling heat transfer performances, especially via breaking the mushroom bubbles and preventing dry-out; microstructured surfaces remarkably enhance both heat transfer coefficients and critical heat flux in boiling process. In the present study, the coupling effect of a uniform electric field and the microstructured surfaces on pool boiling in FC-72 at the liquid subcoolings (Δ T sub) of 5 K, 15 K, 25 K, and 35 K was studied. Four kinds of the microstructured surfaces with different sizes of micro-pin-fins were fabricated and tested, and compared with a reference smooth surface. It was found that the critical heat flux (CHF) enhancement of the smooth surface due to the electric field ranges from 15.2% to 22.5% and increases with liquid subcooling. For the microstructured surfaces, the effects of electric field on CHF are closely related to the liquid subcooling and size of micro-pin-fins. For the surfaces with fin width of 30 μm, the increase of CHF due to the electric field is not sensitive to the liquid subcooling; rather, for the surfaces with fin width of 50 μm, the electric field CHF enhancement decreases with the liquid subcooling. The enhancement of CHF due to the electric field can be explained by the competition of a reduction of the Taylor length and the break of the vapor layer (beneficial to the CHF enhancement) and the field trap effect (not conducive to CHF improvement). The field trap effect on the surface with fin width of 50 μm becomes very strong at Δ T sub = 25 and 35 K; as a result, under these two conditions the CHF is reduced under the action of the electric field. [ABSTRACT FROM AUTHOR]

• A new way was proposed to improve the boiling performance in the low surface tension liquid. • The pinning act of bubbles and the cluster bubble nucleation were coupled. • The boiling performance of the micro-nano composited surfaces are significantly improved. • A unique bubble behavior named "microbubble explosive emission" was observed. • The mechanism of bubble behavior was analyzed by a modified force-energy balance model. A new idea by coupling the pinning act of the micro-pin-fins and the cluster bubble nucleation of nonuniform nanowalls, was proposed to improve the boiling performance on micro-nano composited surface in the low surface tension liquid. To realize this idea, the uniform/nonuniform nanowalls were composited on the smooth surface and micro-pin-finned surfaces. The pool boiling performance of a smooth surface, the uniform/nonuniform nanowall surfaces, micro-pin-finned surface, and micro-nano composited surfaces with uniform/nonuniform nanowalls were tested and compared with each other. Both the heat transfer coefficient (HTC) and critical heat flux (CHF) of the micro-nano composited surface with nonuniform nanowalls (named PFNW2) are significantly increased compared to the micro-pin-finned surface. In addition, small bubble departure diameters, high bubble departure frequency and velocity were also found on PFNW2. A unique bubble behavior, named microbubble explosive emission, was observed, which provides a strong evidence for the effectiveness of the method to enhance boiling heat transfer by coupling the pinning act of the micro-pin-fins and the cluster bubble nucleation. It is suggested that high liquid subcooling and modulated nanostructures for bubble departure promotion are both indispensable for further enhancement of HTC and CHF in low surface tension liquid. Image, graphical abstract [ABSTRACT FROM AUTHOR]