Flow and heat transfer characteristics of supercritical CO2 in a natural circulation loop

Owing to the environmentally benign nature and the special property variation at supercritical pressure, CO2 attracts considerable attention in both science and engineering. The CO2 utilization is regarded as a sustainable way in long term and has become an important global issue. In the present study, a two-dimensional numerical model is used to study the convective flow and heat transfer characteristics of supercritical CO2 natural circulation in a uniform diameter rectangular loop. Parametric influences of the heat sink temperature, the inclination angle of the loop and the temperature difference on the convection motion and heat transfer performance have been studied. For a given temperature difference, the heat sink temperature has great effect on both flow and heat transfer performance. Increasing the inclination angle decelerates the convective flow and heat transfer processes due to the gradual decrease in buoyancy. With the increase of the temperature difference, both the flow rate and heat transfer performance are found to initially increase, reach a peak, and then decrease gradually. The underlying physics is explored.

► We simulate the natural convection of supercritical CO2 in a circulation loop.
► We discuss the optimization problem about the operating temperature conditions.
► Optimizing heat sink temperature provides a significant heat transfer enhancement.
► Increasing the inclination angle decelerates the flow and heat transfer processes.
► Optimizing temperature difference is very important for the steady state performance.