In the present paper, a systematic study of the heat transfer characteristics of water in a new-type vertically-upward internally-ribbed tube has been carried out experimentally. The ranges of the experimental parameters were as follows: the pressure at the inlet of the test section ranged from 12 to 28 MPa, and the mass velocity was from 400 to 1200 kg/m2s, and the internal wall heat flux varied from 300 to 600 kW/m2. The experimental results showed that no matter at subcritical pressures or at supercritical pressures, with the increase in pressure or heat flux, the heat transfer in the internally ribbed tube was weakened, while with the increase in mass velocity, the heat transfer was improved. A systematic comparison between the heat transfer of water in internally ribbed tubes and that in smooth tubes was made in this paper. It was found that compared with the smooth tube, the internally ribbed tube can effectively enhance the heat transfer at subcritical pressures, and also at supercritical pressures. In this paper, the heat transfer enhancement of the internally ribbed tube was attributed to the enlarged heat transfer area, disturbing effect of ribs and the rotational flow in the internally ribbed tube. On the basis of analysis of the effects of tube geometric structures on heat transfer in internally ribbed tubes, a new nondimensional parameter composed of the geometric parameters of the internally ribbed tube was put forward in the present paper to qualitatively compare the capacity of heat transfer enhancement of internally ribbed tubes with different geometric structures, and this new nondimensional parameter got verified by comparison of experimental data of different internally ribbed tubes from open literatures.

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