12. BoilingHeatTransfer_3_web

12. BoilingHeatTransfer_3_web - ENU 4134 Boiling Heat...

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Unformatted text preview: ENU 4134 Boiling Heat Transfer Part 3/3 D. Schubring October 22, 2010 Outline I Introduction to pool and flow boiling I Nucleation superheat I Boiling incipience and bubble departure I Correlations for nucleate boiling heat transfer coefficient I Critical heat flux (CHF) mechanisms I CHF correlations I Film boiling correlations (post-CHF heat transfer) Learning Objectives (1/2) I 2-c-ii Select and implement appropriate boiling heat transfer correlations, with special emphasis given to complexity of correlation vs. time/resources available for analysis I 2-d-i Explain the physical mechanism of critical heat flux (CHF) in pool boiling. I 2-d-ii Explain the physical mechanisms of CHF in flow boiling and identify the conditions (including type of reactor) in which they are seen. I 2-d-iii Select and implement general CHF correlations I 2-d-v Develop familiarity with nuclear-specific terms/acronyms relating to CHF and apply (regulatory) limits to a nuclear system Learning Objectives (2/2) I 5-a Develop familiarity with terminology and mathematical symbols common to nuclear TH, including those symbols which do not map one-to-one to terminology I 5-b Use correlations and/or models to analyze problems in nuclear thermal hydraulics I 5-f Identify TH-related safety limits for light water reactor operation I 5-g Consider conservatism (or lack thereof) present in a model and evaluate implications of this for reactor safety analysis CHF Mechanism Pool Boiling Fluidization of the pool (Kutateladze) liquid is suspended by vapor streams at the wall. Vapor velocity: j g = C 1 ( f- g ) g 2 g 1 / 4 (1) C 1 . 13- . 18. q 00 cr = g j g h fg (2) Remark: critical heat flux does not usually have anything to do with critical flow. The repeated use of the cr subscript can be confusing. CHF Mechanism Pool Boiling (2) Once CHF occurs, film boiling is present. A lower j g ( q 00 ) is necessary to sustain it: j g = C 2 ( f- g ) g ( f + g ) 2 1 / 4 (3) C 2 . 09 (4) q 00 = j g g h fg (5) Mechanism for film boiling limit: stability analysis heavy liquid on top of lighter vapor. (Enrichment: Rayleigh-Taylor instability,on top of lighter vapor....
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This note was uploaded on 02/07/2011 for the course ENU 4134 taught by Professor Schubring during the Spring '11 term at University of Florida.

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12. BoilingHeatTransfer_3_web - ENU 4134 Boiling Heat...

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