Numerical investigations of corrugated tube and Fe3O4 nanoparticles on the mitigation effects of supercritical water heat transfer deterioration

Abstract

When faced with high thermal loads, the dramatic variations in supercritical water (SCW) thermophysical properties can lead to heat transfer deterioration (HTD). Therefore, the present paper first proposes a new mechanism of HTD based on the pseudo boiling theory, and then numerically investigates the mitigation effects of nanoparticles and corrugations on the HTD. By the investigation of SCW in vertically upward smooth tube, the mechanism study illustrates that the pseudo film with the characteristics of low turbulence intensity and thermal conductivity induces the HTD, and the pseudo two-phase flow instability dominates the growth and dissipation of pseudo film. With the help of nanoparticles and corrugations, the wall temperature has a maximum decrease of 348 K, the wall temperature peak mitigation ratio was 33.5%, and the maximum heat transfer enhancement is 164%. Since the corrugations within the corrugated tube (CT) does not change the growth rate of pseudo film, "HTD cycles" occurs in the CT with large corrugation pitch and further deteriorates the overall heat transfer performance. By the inhibition of pseudo film growth and enhancement of gas-like SCW thermal conductivity, the coupling effect of nanoparticles and corrugations can effectively suppress the HTD as well as "HTD cycles".