Perturbation design for supercritical CO2 heat transfer with Helmholtz oscillators: Shifting the paradigm from geometry to dynamics

Heat transfer deterioration (HTD) of supercritical CO2 (sCO2) in tubes remains a critical bottleneck for next-generation solar thermal systems. This work presents a paradigm-shifting strategy for regulating sCO2 heat transfer in horizontal tubes using Helmholtz oscillators, moving beyond conventional structural optimization toward perturbation engineering. Using GPU-accelerated high-fidelity CFD simulations, we demonstrate that the oscillator performance is largely insensitive to cavity geometry: four distinct configurations, cylindrical, square, spherical, and conical, yield nearly identical heat transfer profiles, confirming that active perturbation rather than geometric specificity accounts for the key enhancement mechanism. Performance differences in tandem oscillators arise from the sustainability of perturbation energy. Triple oscillators spaced at 333.3 mm (matching the turbulent decay scale) achieve peak bottom and top heat transfer coefficients of 52,082 and 63,000 W/(m2·K), respectively, with the top-to-bottom ratio converging to 0.8–1.2. This finding leads to definition of the effective perturbation length as a quantitative design criterion. Internally ribbed tubes exhibit dualistic behavior: they hinder heat transfer in the entry region but synergize effectively downstream. This framework is validated under Monte Carlo ray-tracing (MCRT) solar flux and view-factor radiation. Our findings establish perturbation design as a universal paradigm for optimizing sCO2 heat exchangers in solar thermal and boiler applications.