Numerical analysis of heat transfer enhancement on steam condensation in the presence of air outside the tube

In loss-of-coolant accidents, a passive containment heat removal system protects the integrity of the containment by condensing steam. As a large amount of air exists in the containment, the steam condensation heat transfer can be significantly reduced. Based on previous research, traditional methods for enhancing pure steam condensation may not be applicable to steam-air condensation. In the present study, new methods of enhancing condensation heat transfer were adopted and several potentially enhanced heat transfer tubes, including corrugated tubes, spiral fin tubes, and ring fin tubes were designed. STAR-CCM+ was used to determine the effect of enhanced heat transfer tubes on the steam condensation heat transfer. According to the calculations, the gas pressure ranged from 0.2 to 1.6 MPa, and air mass fraction ranged from 0.1 to 0.9. The effective perturbation of the high-concentration air layer was identified as the key factor for enhancing steam-air condensation heat transfer. Further, the designed corrugated tube performed well at atmospheric pressure, with a maximum enhancement of 27.4%, and performed poorly at high pressures. In the design of spiral fin tubes, special attention should be paid to the locations that may accumulate high-concentration air. Nonetheless, the ring-fin tubes generally displayed good performance under all conditions of interest, with a maximum enhancement of 24.2%.