Visualized investigation of subcooled boiling in variable cross-section fin channels

The subcooled boiling of the two kinds of variable cross-section fin channels of triangular porous (TP) fin and transverse direction serrated(TDS) fin was visualized by water as working medium. The effects of volume flow, inlet subcooling degree and heat flux on the onset of the nucleate boiling were investigated. By observing the process of single bubble formation, growth and merging or disengagement in the variable cross-section fin channel, the boiling heat transfer enhancement mechanism was analyzed. The results show that the average cycle of bubbles from the appearance to disappearance in the TDS fin channel is around half of the TP fins; the onset of the nucleate boiling position gradually moves toward the outlet of the flow channel as the volume flow increases. By contrast, it gradually close to the inlet of the channel when the heat flux density increases and the inlet subcooling degree decreases. Furthermore, the effect of the inlet subcooling degree on the onset of the nucleate boiling is greater than that of the heat flux.