Numerical study on heat transfer and pressure drop characteristics of supercritical CO2 in horizontal spirally concaved tubes

The RNG K-ε model is used to simulate the cooling heat transfer characteristics of supercritical CO2 in horizontal spirally concaved tubes and smooth tubes, the velocity field, temperature field and vorticity are compared and analysed, and it is proved that the spirally concaved tube has better heat transfer performance than smooth tube. The change of overall heat transfer performance of spirally concaved tubes is investigated under different inlet Reynolds numbers, inlet pressures, and whether there is buoyancy or not. The results show that the heat transfer coefficient of spirally concaved tubes increases with the increase of the inlet Reynolds number, and the changing trend of the heat transfer coefficient and the specific heat capacity is consistent at different inlet pressures. The heat transfer coefficient of spirally concaved tubes reaches the maximum near the quasi-critical temperature under the conditions of different inlet pressures and inlet Reynolds numbers. The heat transfer intensity can be enhanced with buoyancy, which is mainly manifested near the quasi-critical temperature, and the buoyancy effect caused by gravity becomes more obvious with the increase of Reynolds number. The pressure drop increases with the increase of inlet pressure and Reynolds number, and decreases monotonously with the increase of temperature. With the increase of supercritical CO2 temperature, the pressure drop decreases sharply at low temperature, and begins to change slowly after the quasi-critical temperature.