Flow boiling is an important heat dissipation method for cooling high heat flux surfaces in many indus-trial applications.The heat transfer can be further enhanced by using porous media surfaces due to their high specific surface areas.However,although flow boiling in channels is well understood,the phase-change behavior with the additional capillary effect induced by the porous structures is not well under-stood,and the design of the porous structures is difficult to avoid dryout and over-temperature accidents.A pore-scale lab-on-a-chip method was used here to investigate the flow boiling heat transfer character-istics inside micro-porous structures.The flow patterns,captured in the two-phase region with a uniform pore-throat size of 30 μm,showed that liquid was trapped in the pore-throat structures as both dispersed liquid bridges and liquid films.Moreover,the liquid film was shown to be moving on the wet solid surface by laser-induced fluorescence and particle tracking.A theoretical analysis showed that the capillary pres-sure difference between adjacent liquid bridges could drive the liquid film flows,which helped maintain the coolant supply in the two-phase region.The pore-throat parameters could be designed to enhance the capillary pressure difference with multiple throat sizes of 10-90 μm which would enhance the heat transfer 5％-10％ with a 5％-23％ pressure drop reduction.This research provides another method for improving the flow boiling heat transfer through the porous structure design besides changing the sur-face wettability.