A Study Of Enhanced Heat Transfer Involved In Residual Heat Removal Exchanger

Complete condensation and pool boiling play an important role in the heat transferprocess in the PRHRS（Passive Residual Heat Removal System）of advanced reactors, such asSMART, SBWR and SWR1000. Performance of heat exchanger directly affects the safety andeconomy of nuclear power plants. This paper deals with the heat transfer characteristic ofcomplete condensation and pool boiling involved in the heat exchanger of PRHRS. The outerdiameter of all tubes for experiments is16mm, and saturation pressure ranges from0.08MPato0.4MPa. The main research contents and results are as follows:Complete condensation. Heat transfer of film condensation of pure vapor in verticalsmooth, straight fin and helical micro-fin tubes was studied for their applications in passiveemergency condenser. The results show that, within the experimental ranges, heat transfercoefficient of helical tube is2.7~3.2times, and for straight fin tube,2.8~3.3times as high asthat of smooth tube. The state of condensate film flow in smooth and straight tube is inlaminar-wave regime, while for helical micro-fin tube the upstream inside the tubes is inlaminar-wave regime and turbulence mainly occurs at downstream. Theoretical Nusselt modelfor laminar film condensation is modified by considering the effect of steam velocity andinterfacial shear stress. The modified model well predicted the experimental data.Pool boiling. Heat transfer of pool boiling on vertical smooth,pin-fin tube and poroussurface tube was investigated due to their application in the passive heat exchanger of PRHRS.The result shows that, within the experimental ranges, the heat transfer coefficient of pin-fintube is1.2~1.24times, while for porous tube,2.16~2.44times as high as that of smooth tube.In terms of the bundle experiments, the heat transfer coefficients of smooth tube bundle andporous surface tube bundle increase in some extent, but decline for the case of pin-fin tubebundle.