Experimental study on flow and heat transfer characteristics of supercritical carbon dioxide in 3D printed channels

In the pursuit of higher heat transfer efficiency of microchannel heat exchangers in Supercritical carbon dioxide (sCO₂) Brayton cycle power generation system, the structure of microchannels is becoming increasingly complex. However, limited by the applicability of existing techniques such as chemical etching and diffusion bonding, these structures are difficult to manufacture. 3D printing manufacturing technology offers a significant promise for fabricating micro-scale and complex-structured channels. Unfortunately, the overall performance in 3D printed channels is still not quantitatively evaluated. In this study, straight circular channels fabricated using 3D printed SLM technology with an outer diameter of 6 mm and an inner diameter of 2 mm were fabricated. A systematic experimental study was conducted with a supercritical carbon dioxide flow and heat transfer test platform. Another straight channel made by conventional machining was tested and compared. It was found that the frictional and heat transfer coefficients in 3D printed is much higher than that in conventional machining channel, which is mainly effect by its large roughness height. In the liquid-like region, the Performance Evaluation Criterion (PEC) for 3D printed channel ranged from 1.67 to 2.52; in the pseudocritical region, the PEC ranged from 2.39 to 2.53; and in the gas-like region, the PEC ranged from 1.60 to 2.18. Based on the experimental data obtained, a new heat transfer predictive correlation for 3D printed channels on supercritical carbon dioxide was established. The deviation between predicted value and experiment data is within ± 20 % band.