Helically coiled tubes are widely used in many industrial applications such as the steam generator in the high-temperature gas-cooled reactor which is recognized as one of the new generation advanced reactors. The thermophysical properties of fluids exhibit drastic and fast changes in the pseudocritical region so that the flow and heat transfer characteristics of supercritical pressure fluids are greatly different from those at the subcritical pressure. The paper presents results of numerical investigation on turbulent heat transfer of supercritical CO2 in a helically coiled tube with a tube diameter of 9 mm, a coil diameter of 283 mm and a coil pitch of 32 mm under the constant wall heat flux. Both the RNG k-ε model with enhanced wall function and the SST k-ω model were applied in the simulations, and the results showed that the SST k-ω model agreed better with the experimental results in the literature. Effects of buoyancy and flow acceleration were evaluated. Details of developing heat transfer characteristics at three specific cross sections were analyzed. The heat transfer regularity and mechanism presented in this work can be useful for the design and development of more economic and safer design of the supercritical steam generator.

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