To investigate effects of the location of side inflow holes oil pool boiling heat transfer in a vertical annulus, the location of the holes has been changed from 0.1 to 0.4 m. For the test, a heated tube of 34 mm diameter and the water at atmospheric pressure have been used. To clarify effects of the location of the inflow holes oil heat transfer results of the annulus are compared to the data of a single unrestricted tube and the annulus with closed bottoms. Adoption of the side inflow holes results in higher heat transfer than that of the single unrestricted tube as the heat flux is less than 100 kW/m(2). Moreover, it can remove the possibility of heat transfer deterioration at higher heat fluxes, which is a general characteristic of pool boiling in the annulus with closed bottoms. As the holes arc located at 0.3 in from the bottom Of the tube the most attractive results have been obtained and the enhancement in the heat transfer coefficient is 26.9% comparing to the single unrestricted tube at 160 kW/m(2). (C) 2007 Elsevier Ltd. All rights reserved.