Performance analyses of a steam condensation tube immersed in a saturated water pool: Effects of tube inclination

Two-phase heat exchanger immersed in a passive containment cooling water storage tank (PCCWST) is a key component of the passive containment cooling system (PCCS) in light water reactors. Condensation and boiling heat transfer phenomena taking place on the inside and outside walls are crucial to the performance of the heat exchanger tube. The performances of such phenomena can be readily affected by the inclination angle of the heat exchanger tube under buoyancy-driven convection conditions in a PCCWST. However, to date no systematic examination of the effects of inclination angle on pool heat exchanger performance has been reported. This paper presents the results of numerical and experimental analyses of how inclination angle affects the performance of a single steam condensation tube immersed in a saturated water pool. To concurrently predict the two-phase heat transfer processes inside and outside the heat exchanger tube, an explicit heat structure coupling of two thermal-hydraulic codes was implemented using open media models. An experimental facility was also constructed to test a single-tube heat exchanger under the same conditions as the simulation. A comparison of simulation data and experimental results obtained for the reference case (tube inclination of 30 degrees) confirmed that the coupled code could predict the heat transfer rate in the pool heat exchanger within the error limits of the experimental measurements. In light of this, additional simulations and experiments were conducted at varying inclination angles, from 3 degrees to 90 degrees. The results of simulations and experimental studies revealed that the heat transfer rate of a heat exchanger tube in a saturated pool is hardly influenced by tube inclination. Although an increase in inclination angle caused the vapor slug to spread around the heat exchanger tube surface, preventing liquid from getting to the surface of the tube, thereby decreasing boiling heat transfer coefficients, this was compensated for by an increase in condensation heat transfer coefficients as the inclination angle increased as a result of accelerated condensate liquid film in the tube. Thus, the overall effect of inclination angle on the thermal performance of a single-tube pool heat exchanger is inconsequential.