p3.3-2 - laser pulse occurs c Assume that the slab is much...

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3.3-2 A laser machining process uses a very short but very high power heat flux to melt the surface of an aluminum slab. Initially the aluminum slab is at a uniform temperature, T in =20ºC. The aluminum has a density of ρ =2700 kg/m 3 , a specific heat capacity of c =900 J/kg-K, and a thermal conductivity of k =240 W/m-K. The heat flux from the laser is applied to the surface of the aluminum and lasts only τ laser = 0.1 ms. You would like to heat the temperature of the aluminum at the surface of the slab to its melting temperature, T melt =630ºC. a.) Estimate how thick the slab must be in order to treat it as a semi-infinite solid. b.) Estimate the laser heat flux (W/m 2 ) that is required to carry out the machining process (i.e., to bring the material to its melting temperature after laser ). Assume that no convection or radiation occurs from the surface during the period of time that the
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Unformatted text preview: laser pulse occurs. c.) Assume that the slab is much thicker than your answer from part (a) and that you’ve applied a heat flux that is consistent with your answer from part (b). Sketch the temperature distribution in the aluminum at various times. The sketch need not be exact, but should capture the qualitative features correctly; these include the approximate temperature and positions. Include sketches for the following times: • at t = 0 (i.e., the onset of the laser power), • at t = 0.05 ms (i.e., half-way through the heating process), • at t = 0.1 ms (i.e., the end of the heating process), • at t = 0.2 ms (i.e., 0.1 ms after the heating process has ended), and • at t = 0.4 ms (i.e., 0.3 ms after the heating process has ended)....
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