To identify effects of the bottom inflow area on pool boiling heat transfer in a vertical annulus, three tube diameters (16.5, 25.4, 2 34.0 mm) and the saturated water at atmospheric pressure has been tested. The inflow area has been changed from 0 to 1060.3 mm To clarify effects of the inflow area on heat transfer results of the annulus are compared to the data of a single unrestricted tube. The inflow area changes heat transfer coefficients much and moves the deterioration point of heat transfer coefficients to the higher heat fluxes. To quantify effects of the inflow area on heat transfer, a new empirical correlation has been developed in terms of the area ratio, inflow area, and the heat flux. The correlation predicts the heat transfer data of boiling within 10%. (c) 2007 Elsevier Ltd. All rights reserved.