CFD Prediction of Heat Transfer Deterioration to Supercritical Water

• Supercritical water will serve as a coolant in the Generation-IV Supercritical Water-Cooled Reactor (SCWR). The important advantage of supercritical water as a coolant is the lack of the phase-change phenomenon. As a result one of the most limiting factors applicable to the current Light Water Reactors (LWR) – namely the occurrence of the Critical Heat Flux (CHF) – is no longer existent. Considering the high heat capacity, supercritical water is indeed an excellent choice for a coolant. However, even though CHF is no longer an issue, heat transfer to supercritical water suffers from a sudden Heat Transfer Deterioration (HTD) phenomenon. HTD manifests itself with a sudden reduction of the local heat transfer coefficient and local increase of the heater wall temperature. Even though the phenomenon has been intensively investigated in the past 50 years, there is a lack of a robust and accurate criterion for the onset of HTD. Recently, Palko and Anglart (2007) demonstrated that the onset of HTD can be captured with a computational model based on the Reynolds Averaged Navier Stokes (RANS) equations and using the Shear-Stress Transport (SST) turbulence model implemented in the CFX code (Menter, 1993).  The calculations revealed that there are two principal mechanisms of the onset of HTD: (a) reduction of the turbulence intensity close to the wall due to the buoyancy effects, (b) creation of a thin layer of supercritical water with low thermal conductivity (corresponding to the “vapor” phase of the supercritical fluid). The former mechanism occurs for relatively low mass fluxes, whereas the latter occurs when the mass flux of coolant is pretty high. The present paper presents further numerical investigation of the HTD phenomenon, and in particular, a derivation of the criterion for the onset of HTD based on numerical simulations.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

Nyckelord

SRA - Energy

SRA - Energi

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