Advancement of supercritical carbon dioxide Brayton cycle technology in concentrated solar power plants requires an improved understanding of duct-flow convection in the supercritical region. Numerical simulation, based on a modified carbon dioxide hot gas bypass load stand with an external heat source, is conducted to determine carbon dioxide convective heat transfer coefficients at supercritical pressures and temperatures beyond the range for which results are available in the literature.
The simulation geometry is derived from the heated test section included in the physical load stand. Inlet pressure, temperature, and mass flux are varied to assess the influence on Nusselt number. Cases that achieve fully developed flow and temperature conditions inside the tube geometry agree with predictions from a Nusselt number correlation in the literature with a mean absolute error of 6.4 percent, less than the 6.8% average error reported for the correlation. This agreement includes pressure and temperature conditions outside the defined range of the correlation. Future experiments will provide additional validation of the model and correlation, enabling analysis farther into the supercritical region necessary for Brayton cycle operation.
Heat transfer and pressure drop characteristics during the in-tube cooling process of carbon dioxide in the supercritical region
