Experimental investigation of supercritical CO2 heat transfer characteristics in a three-rod bundle

Abstract

The investigation of the heat transfer properties of supercritical CO₂ (SCO₂) within rod bundles is crucial for optimizing the design of the supercritical CO₂ direct-cooled reactor. This study presents an experimental study on the heat transfer characteristics of supercritical CO₂ in a three-rod bundle. The experiments were conducted under pressures ranging from 8 to 11 MPa, heat fluxes from 31 to 123 kW/m², mass fluxes from 270 to 830 kg/(m²·s), and inlet temperatures from 5 to 114 °C. The internal wall temperature of the heated rod was measured with a sliding thermocouple device. To assess the accuracy of the measurements, a validation experiment was performed by comparing the temperature readings from the sliding thermocouple with those from a fixed thermocouple over a temperature range from room temperature to 350 °C. The maximum difference between the two measurements was approximately 3 °C, confirming the reliability of the sliding thermocouple measurements. The effects of heat flux, mass flux, and pressure on heat transfer were systematically analyzed. Seven heat transfer correlations based on tube data and three correlations derived from rod bundle data were evaluated with the experimental results. The findings reveal that the Jackson 1 correlation exhibits the highest agreement with the experimental data. Furthermore, two new correlations were developed based on the section-averaged wall temperature and section-maximum wall temperature, respectively. These newly proposed correlations not only enhance prediction accuracy but also increase their utility for practical applications.