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Boiling_Examples_1_2

# Boiling_Examples_1_2 - Boiling Heat Transfer Example 1...

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Boiling Heat Transfer – Example 1 & 2 (Subcooled/Onset-of Boiling) – D. Schubring 1 Example 1 Problem 12-1 in T&K: Calculate the relation between superheat and equilibrium bubble radius for water at 1 atmo- sphere (Equations 12-7 and 12-8 in T&K). Consider bubbles of 10 μ m radius and get concrete answers. Equation 12-7: T b - T sat = RT b T sat h fg ln 1 + 2 σ p l r ? (1) R = 461 . 5 J kg - 1 K - 1 (2) p l = 1 . 01 × 10 5 Pa (3) h fg = 2 . 257 × 10 6 J kg - 1 (4) σ = 0 . 05878 N m - 1 (5) T sat = 373 K (6) T b - T sat = 461 . 5 T b T sat 2 . 257 × 10 6 ln 1 + 2 × 0 . 05878 1 . 01 × 10 5 r ? (7) T b - T sat = 461 . 5 T b × 373 2 . 257 × 10 6 ln 1 + 1 . 16 × 10 - 6 r ? ! (8) T b - T sat = 0 . 0763 T b ln 1 + 1 . 16 × 10 - 6 r ? ! (9) ψ = 0 . 0763 ln 1 + 1 . 16 × 10 - 6 r ? ! (10) T b - T sat = T b ψ (11) T b - T sat = ( T b - T sat + T sat ) ψ (12) T b - T sat = ( T b - T sat ) ψ + T sat ψ (13) ( T b - T sat ) (1 - ψ ) = T sat ψ (14) T b - T sat = 373 ψ 1 - ψ (15) Equation 12-8: T b - T sat = 2 σT sat vol fg h fg r ? (16) vol fg = 1 . 672 m 3 kg - 1 (17) T b - T sat = 2 × 0 . 05878 × 373 × 1 . 672 2 . 257 × 10 6 × r ? (18) T b - T sat = 3 . 25 × 10 - 5 r ? (19) For 10 μ m bubbles: Equation 12-7: ψ = 0 . 0763 ln 1 + 1 . 16 × 10 - 6 r ?

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Boiling_Examples_1_2 - Boiling Heat Transfer Example 1...

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