Abstract: On the basis of our experimental observation an analysis of boiling heat transfer mechanism in narrow space is developed and a model of boiling heat transfer is provided as fol-lows:There exists a eritical gap size(Bond=0.6) which identifies two boiling regimes.For the su-per-critical channels with Bond ≥0,6,two-phase heat transfer is assumed to be a superposition of pool boiling and liquid convective components.For subcritical channels(Bond <0.6), since each elementary portion of the wall surface is periodically washed either by a thin liquid film or by a liquid plug,the heated surface is first cooled by evaporation for the time duration during which it is covered by the coalcsced bubble; liquid flows into the space immediately after the bubble passes. Flow along the heated surface is taken into account.The results predicted from the model are consistent with the experimental heat transfer data The influence of gap sizes,plate heights,and heat fluxes on heat transfer is given and discussed. There exists an optimum channel size of heat transfer enhancement.

Key words: narrow space, boiling. heat transfer mechanism