Experimental Investigation on Heat Transfer Characteristics of Vertical Rifled Tube at Low Mass Flux Under Subcritical and Nearcritical Pressure

Within the range of pressure from 12 to 21MPa,mass flux from 232 to 773 kg/(m2·s),and inner wall heat flux from 132 to 663 kW/m2,an in-depth experiment was conducted at low mass flux to investigate the flow boiling heat transfer characteristics of steam-water in vertical upward rifled tube.The rifled tube is φ32 mm×6.3 mm SA-213T12 carbon steel.The tube wall temperature distribution was obtained in the experiment.The effects of pressure,inner wall heat flux and mass flux on heat transfer were analyzed,the heat transfer deterioration mechanism was discussed,and the corresponding empirical correlations were also presented.The experimental results show that dryout can occur in vertical upward rifled tube,but departure from nucleate boiling(DNB) has not been captured.With the increase of pressure and inner wall heat flux,and with the decrease of mass flux,dryout occurrs ahead and the wall temperature in post-dryout region increases obviously.Compared with the heat transfer performance of rifled tube at subcritical pressure,that in nearcritical pressure region gets worse,the wall temperature significantly rises,and the critical enthalpy decreases.