Experimental Investigation On Behaviour Of Subcooled Boiling Heat Transfer Enhancement By Multi-Layered Micro/Nano Structured Surface

It is of great significance to enhance heat transfer efficiency and critical heat flux(CHF)of subcooled boiling for promotion of heat fatigue and heat shock resistance of plasma facing component(PFC)in fusion reactor.The multi-layered micro/nano structures were created on the subcooled boiling surface with microstructural metal mesh and the nanoscale metal powder through vacuum brazing.Comparing the surface topographic characteristics of the cases manufactured with metal mesh of different aperture width scales with those of smooth surface case,it is founded that three layers of composite micro/nano structures with different scales were successfully generated on metal surfaces by the proposed technique.They are cavity,pore and nano pillar structures.The comparison of contact angles with water shows that the composite micro/nano structures on surfaces reduce the hydrophily to some degree but do not change to hydrophobic state.Further macro-photographic measurements show that the bubble densities generated on composite micro/nano structured surface cases in subcooled boiling are several times higher than that on smooth surface,especially for case manufactured with smaller aperture width scale metal mesh.However,there is a critical aperture width scale of metal mesh,i.e.,120p?m.The case with smaller aperture width than the critical value presents subtler increase of bubble generation density.With comprehensive high heat flux experimental platform,the subcooled boiling heat transfer performance experiments were conducted with smooth surface pipe and a set of composite structured surface pipes to test the heat transfer performance of micro-nano surface quantitatively.In addition,we make the comparison of heat transfer effect between the composite structured surface and the fin structure surface.It is concluded that in addition providing much more boiling nucleus,the composite micro/nano structures can induce more complex flow instability on boiling surface so that the vapor filming generation will be delayed effectively,which will be beneficial to CHF(critical heat flux)promotion.The critical heat flux on the surface of multi-layer composite micro-nano structure is 80%higher than that on the smooth surface at least,and the heat transfer effect is obviously better than the smooth surface and traditional finned structure surface.The results provide some reference to the advanced fusion PFC heat transfer technology development.