Heat transfer characteristics of supercritical CO2 flow in metal foam tubes

To report an improved supercritical CO2 (SCO2) Rankine cycle by optimizing the heat transfer performance of the gas heater, experimental work was conducted to investigate the forced convective heat transfer and pressure drop performance of SCO2 heated in tubes partially filled with metal foam by interring copper fibers on the inner wall. The effects of operating conditions (8300 < Re-b < 25,000, heat flux Phi = 150/250/350 W) and foam structure parameters (porosity epsilon = 0.85/0.9/0.95 and pore density omega = 20/40/60) were studied. The experimental result first revealed the metal foam-based heat transfer enhancement in SCO2 is about 1.5-5.0 times. It was found that decreasing epsilon or omega can make the heat transfer coefficient first decrease and then increase; the pressure drop, however, is reduced to a constant value; the comprehensive performance (j/f) of the foam tube with omega/epsilon = 40/0.95 is better. Finally, new correlations of both the heat transfer and the friction factor linked to the buoyant force were proposed. The errors of both correlations are within +/- 15%. (C) 2015 Elsevier B.V. All rights reserved.