20pts 8238 k1675 c563 lc15mmrt002ti300ktinf1500 h20

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Unformatted text preview: bricated from AISI 316 stainless steel and is of thickness L = 15 mm. One surface of the wall is coated with a thin ceramic film that has a thermal resistance R”t = 0.02 m2‐K/W. The opposite surface is insulated from the surroundings. When the furnace starts up, the wall is at a temperature Ti = 300 K and combustion gases at T∞ = 1500 K with an h = 20 W/m2‐K. How long will it take for the inner steel to reach a temperature of 1200 K? What is the temperature of the exposed surface of the ceramic film at this time? (20 pts) ρ = 8238 k=16.75 c=563 Lc = 15 mm Rt = 0.02 Ti = 300 K Tinf = 1500 h = 20 T = 1200 Need to add contact resistance to the h to use Bi. U = (Rt + 1/h)‐1 = 19.2 Bi = ULc/k =19.2*.015/16.75 = .02 can use lumped capacitance t := − rho ⋅ Lc⋅ cap U ⋅ ln⎛ ⎜ ⎝ Ti − Tinf ⎠ temp − Tinf ⎞ t = ‐8238*.015*563/19.2* ln(1200 – 15...
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This note was uploaded on 11/12/2010 for the course CHEN 3320 at Colorado.

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