Abstract
Numerical simulation has been widely used in nuclear reactor safety analyses to gain insight into key phenomena. The Critical Heat Flux (CHF) is one of the limiting criteria in the design and operation of nuclear reactors. It is a two-phase flow phenomenon, which rapidly decreases the heat transfer performance at the rod surface. This paper presents a numerical simulation of a steady state flow in a vertical pipe to predict the CHF phenomena. The detailed Computational Fluid Dynamic (CFD) modeling methodology was developed using FLUENT. Eulerian two-phase flow model is used to model the flow and heat transfer phenomena. In order to gain the peakwall temperature accurately and stably, the effect of different turbulence models and wall functions are investigated based on different grids. Results show that O type grid should be used for the simulation of CHF phenomenon. Grids with Y+ larger than 70 are recommended for the CHF simulation because of the acceptable results of all the turbulence models whileGrids with Y+ lower than 50 should be avoided.To predict the dry-out position accurately in a fine grid, Realizable k-e model with standard wall function is recommended.These conclusions have some reference significance to better predict the CHF phenomena of vertical pipe. It can also be expanded to rod bundle of Boiling Water Reactor (BWR) by using same pressure condition.
Highlights
Critical Heat Flux (CHF) is a two-phase flow phenomenon that is characterized by a heat transfer mechanism change which rapidly decreases the efficiency of the heat transfer performance at the heater surface
Based on Eulerian two-phase model, this paper presents numerical simulations of CHF phenomenon by the use of Computational Fluid Dynamic (CFD) method to investigate the effect of different grids, turbulence models and wall functions
For two phase flow, a little difference is found among three grid types
Summary
Critical Heat Flux (CHF) is a two-phase flow phenomenon that is characterized by a heat transfer mechanism change which rapidly decreases the efficiency of the heat transfer performance at the heater surface. Zhang et al (2015) has analyzed the effect of grids and turbulence models for subcooled boiling flow in a vertical pipe. It is still not clear that if the turbulence models have the same performance on CHF phenomena as that of subcooled boiling flow, especially on the value and position of highest wall temperature.
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