Single-phase and flow boiling heat transfer for distilled water in the narrow annuli (5=1.5 mm) have been experimentally investigated. The parameter ranges examined are: mass velocity from 48 to 268 kg/m~2; heat fluxes from 4.9 to 39.1kW/m~2 for inside tube and from 4.2 to 55.6 kW/m~2 for outside tube; mass quality in boiling heat transfer from 0.02 to 0.88; system pressure from 1.5 to 6.0MPa. The single-phase heat transfer coefficient can be predicted using the modified Dittus-Boelter correlation. It is found that the boiling heat transfer is strongly influenced by heat flux, while the effect of mass velocity and mass quality are very slight. This shows that the boiling heat transfer is mainly via nucleate boiling. The data are used to develop a new correlation for boiling heat transfer in narrow annuli. The con-elation is then compared with the experimental data; the mean deviation is less than 13%.
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