Abstract
Experiments of flow boiling of water at 0.11MPa were conducted in a vertical narrow annulus for the inlet subcooling of 10 to 50 K and mass velocity of 100 to 750 kg/m^2s. Measured boiling curves show existence of enhancement regions of heat transfer. Visual observation identified flow patterns peculiar to narrow space. Isolated bubbles generated at lower heat fluxes are deformed and spread rapidly over the whole narrow annulus. At higher heat fluxes, the narrow space are filled with vapor mass and dry patches are seen on the heating tube Flow patterns are different from those in conventional large tubes
