Effect of axially varying heat flux on thermo-hydraulic characteristics and circulation ratio of riser tubes of natural circulation boiler
2022
Hossain, Md Naim | Ghosh, Koushik | Manna, Nirmal K.
The present paper shows that the axial non-uniformity of the heat flux under actual furnace conditions for a riser-downcomer system of the natural circulation steam generator significantly impacts the two-phase thermal-hydraulics and circulation ratio (CR). Based on a regression analysis, a regression factor (k-factor) is introduced to take into account the axial variation of the heat flux under real furnace conditions. The analysis reveals that heat flux variation with a different k-factor alters the quality distribution, mass flux, and onset of critical heat flux (CHF) significantly compared to the uniform heat flux condition. It is also observed that beyond a pressure of 100 bar, the axially varying heat flux significantly alters the critical circulation ratio. The safe circulation ratio under different axial variations of heat flux for the entire range of operating pressure of the natural circulation boiler is proposed using the present model. Finally, the CR of a typical 800 MW steam generator with real furnace heat flux variation is predicted under critical, safe, and optimal design conditions.
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