Numerical and Experimental Study on Thermal-Hydraulic Behaviors in the Secondary Side of Passive Residual Heat Removal Heat Exchanger

Passive residual heat removal heat exchanger (PRHR HX), as a key component of the passive residual heat removal system (PRHRS) in the advanced reactors of CAP1400 and AP1000, should have sufficient heat transfer capacity to remove core decay heat during the accidents. In this paper, experiments and numerical simulations are constructed to explore the secondary side flow and heat transfer characteristics of a miniaturized PRHR HX that comprises 6 x 7 C-shaped tubes located in the center of a rectangular tank. In the three-dimensional (3D) numerical simulation, the C-shaped tubes are simplified as porous media and the drift flux model with the distributed resistance method is employed to simulate the two-phase flow in the secondary side of PRHR HX. The heat removal rate and mass transfer rate in the tank are estimated using empirical correlations. In the test, both the primary side and secondary side temperatures are measured. The bubbles generated on the tube outer walls are recorded using a high-speed camera. The local outer wall temperatures, total heat transfer rate and local water temperatures are all compared with experimental values to verify the simulation. The maximum deviation of the calculated heat transfer rate is less than 4.5%. The details about the secondary side flow conditions and bubble behaviors are analyzed. (C) 2020 Elsevier Ltd. All rights reserved.