Experimental And Numerical Study On Flow And Heat Transfer To Supercritical Water Flowing In Annular Channel

Compared to traditional PWR, supercritical water cooled reactor (SCWR) hasadvantages like higher thermal efficiency and a more simplified system. However,there are still many technical problems when it comes to the reactor design. It is verydifficult to explore the characteristics of flow and heat transfer due to a drasticvariation in physical properties around pseudo-critical point, especially near theregion where spacer grid exists. So far, a widely acknowledged theory on the heattransfer to supercritical water has not been achieved. In this thesis, heat transferexperiments of supercritical water flowing in an annular channel on SWAMUP loopin SJTU have been performed and CFD simulations have been applied to analyze theflow and heat transfer characteristics of supercritical water.The experimental results suggest that the wall heat flux has a significantinfluence on the heat transfer. The heat transfer coefficient decreases with the increaseof the wall heat flux. Furthermore, the geometry of spacer grid has a great effect onthe decay of grid-enhanced heat transfer in downstream locations. The heat transferdecays in various patterns of manifestation under different pressure conditions.Among many traditional heat transfer correlations, Bishop-correlation has the bestprediction of the heat transfer coefficient of supercritical water flowing in the annularchannel. The numerical simulation results indicate that the heat flux influences theheat transfer coefficient by changing the physical property of water near the heatingwall. When the heat flux increases, the decrease of turbulence intensity of the mainregion and thermal conductivity near the heating wall becomes the main reason ofheat transfer coefficient reducing. The CFD method did not predict the decay of theenhanced heat transfer well because it could not simulate the flow condition andphysical property in the downstream locations of spacer grids. There is a greatdistinction between rod bundles and the annular channel in the aspects of flow conditions and the heat transfer. In rod bundles, the mass flux and the temperaturedistributions of water are not uniform in sub-channels. In addition, the coolant mixesintensively on the same section. The two reasons above make the heat transferdifferent on various circumference locations of the same heating rod.