Boiling_Examples_5_6_7

Boiling_Examples_5_6_7 - Boiling Heat Transfer – Example...

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Unformatted text preview: Boiling Heat Transfer – Example 5, 6, & 7 (CHF and Everything After) – D. Schubring 1 Example 5 Evaluation of pool boiling CHF and minimum heat flux to sustain film boiling: T sat = 100 ◦ C (1) g = 9 . 81 m s- 2 (2) C 1 ≈ . 15 (3) C 2 ≈ . 09 (4) σ = 0 . 05878 N m- 1 (5) ρ f = 958 kg m- 3 (6) ρ g = 0 . 598 kg m- 3 (7) h fg = 2 . 257 × 10 6 J kg- 1 (8) CHF: j g = C 1 " σ ( ρ f- ρ g ) g ρ 2 g # 1 / 4 (9) j g = 0 . 15 . 05878(958- . 598)9 . 81 . 598 2 1 / 4 (10) j g = 0 . 940 m s- 1 (11) q 00 = j g ρ g h fg (12) q 00 = 0 . 940 × . 598 × 2 . 257 × 10 6 (13) q 00 = 1 . 27 × 10 6 W m- 2 = 1 . 27 MW m- 2 (14) Minimum stable film boiling: j g = C 2 " σ ( ρ f- ρ g ) g ( ρ f + ρ g ) 2 # 1 / 4 (15) j g = 0 . 09 " . 05878(958- . 598)9 . 81 (958 + 0 . 598) 2 # 1 / 4 (16) j g = 0 . 0141 m s- 1 (17) q 00 = j g ρ g h fg (18) q 00 = 0 . 0141 × . 598 × 2 . 257 × 10 6 (19) q 00 = 1 . 90 × 10 4 W m- 2 = 19 . kW m- 2 (20) Consider: if CHF occurs at full power, could even a shutdown collapse a stable film (decay heat)? (Note: flow boiling is not quite the same as film boiling and there is also a property effect with the 70-155 times higher pressure.) Boiling Heat Transfer – Example 5, 6, & 7 (CHF and Everything After) – D. Schubring 2 Example 6a Example of the Bowring correlation (Problem 12-5 in T&K) Given: D = 0 . 01 m (21) L = 3 . 66 m (22) G = 2000 kg m- 2 s- 1 (23) P = 6 . 89 MPa (24) T in = 204 ◦ C (25) h fg = 1 . 51 × 10 6 J kg- 1 (26) Δ h sub = 0 .....
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This note was uploaded on 10/22/2011 for the course ENU 4134 taught by Professor Schubring during the Fall '11 term at University of Florida.

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Boiling_Examples_5_6_7 - Boiling Heat Transfer – Example...

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