| 1. |
- Dong, Shichang, et al.
(author)
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Critical heat flux characteristics for subcooled flow boiling on an inclined downward-heating surface in a divergent channel
- 2024
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 255
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Journal article (peer-reviewed)abstract
- To have a deep understanding on the critical heat flux (CHF) characteristics of ex-vessel core catcher system, the present study conducted subcooled flow boiling experiments on an inclined downward-heating surface in a diverging channel. The effects of inlet mass flux (100 kg/m2s to 400 kg/m2s), subcooling (1 K to 30 K) and inclination angle (5° to 45°) on the CHF were investigated. A high-speed camera and pressure transducer were used to simultaneously record the two-phase flow behavior and pressure. The results show that with the increase of heat flux, the small bubbles grow and coalesce into a bubble blanket gradually. The condensation of bubble blanket outside the heating surface induces the reversal of downward liquid. Beyond the subcooling threshold (ΔTin ≥ 20 K for θ = 5° and ΔTin ≥ 25 K for θ ≥ 15°), a two-phase flow instability characterized by the pressure shock was observed, which leads to a remarkable enhancement in CHF. An increase in the inclination angle also leads to an increase in CHF, but with a declining slope. The effects of key parameters on the characteristics of the bubble blanket were further analyzed. Especially, the reduced inclined angle makes it easier for bubble blanket to form, and it's easier for the reversible and irreversible dry patches to be formed on the wall. The dry patch fraction is much larger so that the hovering time is much longer and the frequency is lower, so the CHF decreases. And then, a dimensionless correlation between the bubble blanket parameters and the thermal–hydraulic parameters (mass flux, subcooling and inclination angle) was developed.
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| 2. |
- Dong, Shichang, et al.
(author)
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Mechanistic critical heat flux model development for subcooled flow boiling based on superheated liquid sublayer depletion
- 2022
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In: Progress in nuclear energy (New series). - : Elsevier BV. - 0149-1970 .- 1878-4224. ; 153, s. 104445-
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Journal article (peer-reviewed)abstract
- Critical heat flux (CHF) refers to the limit of boiling transfer systems, and crossing this limit may jeopardize system safety. However, a clear understanding of the physical mechanisms of CHF is still lacking. In this study, a new CHF prediction model based on superheated sublayer depletion was established for subcooled flow boiling in an upward vertical tube at low pressure. The model is characterized by its developed determination of the superheated liquid sublayer thickness, net vapor generation location, forced convection heat transfer and liquid supplement caused by bubble turbulent fluctuations. The proposed CHF model was validated by a database covering the low pressure subcooled operational ranging over P = 0.1-2.15 MPa, G = 0.7-35 Mg/m2s, Delta Tin = 11-183.16 K, D = 0.7-12 mm, L/D = 4.2-115.55, and xeqout = -0.2673-0.0843. The model can accurately predict the trend of thermal-hydraulic and geometric factors' effects on the CHF. The prediction results have good prediction accuracy with an root-mean-square error (RMSE) of 15.21%, and overall error of +/- 25%. The proposed model also shows good adaptation to a non-water (refrigerant 113 and liquid nitrogen) system.
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| 3. |
- Dong, Shichang, et al.
(author)
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Theoretical model for subcooled upward flow boiling heat transfer and critical heat flux for an inclined downward heated surface
- 2023
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 213
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Journal article (peer-reviewed)abstract
- The in-vessel retention system and ex-vessel retention system are very important to the safety of nu-clear power plants under severe accidents. While the success of such safety systems relies on well un-derstanding the corresponding physical mechanisms of boiling heat transfer and critical heat flux (CHF). Challenges till remain in accurately predicting the subcooled flow boiling curve especially in the low-pressure and low-flow conditions due to its complex boiling phenomenon. The present study introduces a theoretical model to predict the boiling curve and critical heat flux for subcooled flow boiling in in-clined downward heated rectangular channel. The proposed model well estimates the transition from forced convection, isolated bubble nucleate boiling to fully developed boiling regime by considering the growth and interaction of bubbles. Through probability analysis of bubbles' interaction, the proportion of heat flux in different boiling regimes is determined. In addition, the flow boiling CHF is predicted based on the probability analysis of dry spots. The new model is validated by the subcooled flow boil-ing experiments with vertical single-side heated channel under low-pressure and low-flow conditions. The predicted boiling curves are consistent with experimental results corresponding to different thermal-hydraulic parameters, such as pressure, mass flux, inlet subcooling and wall wettability (hydrophilic and hydrophobic), and the prediction error of CHF is within & PLUSMN;15%. Furthermore, the inclination effect on CHF is validated by the subcooled flow boiling experiments in inclined channel with the inclination angle varying from 0 & DEG; to 90 & DEG;, which shows the good applicability of the developed model.
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