problem4-19 - PROBLEM 4.19 KNOWN: Relation between maximum...

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Unformatted text preview: PROBLEM 4.19 KNOWN: Relation between maximum material temperature and its location, and scanning velocities. FIND: (a) Required laser power to achieve a desired operating temperature for given material, beam size and velocity, (b) Lag distance separating the center of the beam and the location of maximum temperature, (c) Plot of the required laser power for velocities in the range 0 ≤ U ≤ 2 m/s. SCHEMATIC: r b = 0.1 mm T max = 200°C = 2000 kg/m 3 c = 800 J/kg•K k = 27 W/m•K T 2 = 25°C U = 2 m/s ′ q δ ρ α = 0.45 r b = 0.1 mm T max = 200°C = 2000 kg/m 3 c = 800 J/kg•K k = 27 W/m•K T 2 = 25°C U = 2 m/s ′ q δ ρ α = 0.45 ASSUMPTIONS: (1) Steady-state conditions, (2) Constant properties, (3) Semi-infinite medium, (4) Negligible heat loss from the top surface. ANALYSIS: The thermal diffusivity of the materials is 3- = k/ ρ c = 27 W/m K / (2000 kg/m 800 J/kg K) = 16.9 × 10 m /s α ⋅ ⋅ ⋅ 6 2 (a) The Peclet number is -6 2 b Pe = Ur / 2 = 2 m/s × 0.0001 m / ( 2 × 16.9 × 10 m /s) = 8.38Pe = Ur / 2 = 2 m/s × 0....
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This note was uploaded on 12/07/2010 for the course MAE Heat Trans taught by Professor Lee,j.s. during the Spring '10 term at Seoul National.

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problem4-19 - PROBLEM 4.19 KNOWN: Relation between maximum...

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