Flow impinging effect of critical heat flux and nucleation boiling heat transfer on a downward facing heating surface
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Huai-En Hsieh
Abstract
Boiling heat transfer has a high heat removal capability in convective cooling. However, the heat removal capability of downward-facing boiling is significantly worse than that of upward-facing cases because of the confined buoyancy effect. This study was inspired by the conception of external reactor vessel cooling (ERVC) condition relevant to the in-vessel retention (IVR) design of Westinghouse AP1000 plant. In the present study, a small-scale test facility had been established to investigate the local phenomena of boiling heat transfer under a downward-facing horizontal heated surface with impinging coolant flow. In this study, the surface temperature, heat flux information and several specific scenes of bubbles are taken down throughout the boiling processes for detailed investigation. It is observed that bubbles are confined under the downward-facing heated surface, which causes a worse heat transfer rate and a lower critical heat flux (CHF) limit than upward-facing boiling. Nevertheless, the impinging coolant flow is found to disturb the thermal boundary layer formed by the heated surface, so the CHF increases with an increase of coolant flow rate. In addition, during nucleate boiling, it is discovered that the growth, combination and dissipation of bubbles induce turbulent wakes and therefore enhance the heat transfer capability.
Kurzfassung
Die Wärmeübertragung beim Sieden hat eine hohe Wärmeabfuhrfähigkeit bei konvektiver Kühlung. Die Wärmeabfuhrfähigkeit bei abwärts gerichtetem Sieden ist jedoch deutlich schlechter als in aufwärtsgerichteten Fällen wegen des eingeengten Auftriebseffekts. Diese Studie wurde angeregt durch externe Kühlungsbedingungen für das Reaktorgefäß (ERVC) relevant für die Ausgestaltung einer Westinghouse AP1000 Anlage. In der vorliegenden Arbeit wurde eine kleine Testeinrichtung errichtet um die lokalen Strömungsphänomene bei der Wärmeübertragung zu untersuchen. Dabei wurde beobachtet, dass die Blasen unter der nach unten gerichteten Wärmeoberfläche eingeengt sind, was eine schlechtere Wärmeübertragungsrate und einen niedrigeren Wärmefluss verursacht als aufwärtsgerichtetes Sieden. Es wurde festgestellt, dass der aufprallende Kühlmittelfluss die von der erwärmten Oberfläche gebildete thermische Grenzschicht stört was zu einer Erhöhung der Strömungsgeschwindigkeit des Kühlmittels führt. Zusätzlich dazu wurde beim Blasensieden beobachtet, dass das Wachstum, die Kombination und die Dissipation der Blasen Randwirbel erzeugt und deshalb die Wärmeabfuhrfähigkeit verstärken kann.
References
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© 2015, Carl Hanser Verlag, München
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Articles in the same Issue
- Contents/Inhalt
- Contents
- Summaries/Kurzfassungen
- Summaries
- Technical Contributions/Fachbeiträge
- Evaluation of A-dependence of cross-sections for light charged particle production in proton induced reactions at intermediate energies
- Sensitivity study with respect to direction of ADI method during re-flooding in AHWR
- Experimental investigation of thermal mixing phenomena in a tee pipe
- Flow impinging effect of critical heat flux and nucleation boiling heat transfer on a downward facing heating surface
- Operating experience feedback from safety significant events at research reactors
- Review of regulatory requirements relevant to calibration of monitoring instruments in research reactors
- The dust characteristics in the collisional plasma sheath at the presence of external magnetic field
- Shamir Secret Sharing Scheme with Dynamic Access Structure (SSSDAS): case study on nuclear power plant
- Criticality calculations with PN approximation for certain scattering parameters of Anlı-Güngör and Henyey-Greenstein phase functions in spherical geometry
- An analytical approach for a nodal formulation of a two-dimensional fixed-source neutron transport problem in heterogeneous medium
- Evaluation of gross radioactivity in foodstuffs
- Development of gamma spectroscopy employing NaI(Tl) detector 3 inch × 3 inch and readout electronic of flash-ADC/FPGA-based technology
