Question

A young engineer is asked to design a thermal protection barrierfor a sensitive electronic device that might be exposed toirradiation from a high-powered infared laser. Having learned as astudent that a low thermal conductivity material provides goodinsulating characteristics, the engineer specifies use of ananostrutured aerogel, characterized by a thermal conductivity ofKa = 0.005 W/m-K, for the protective barrier. The engineer'sboss questions the wisdom of selecting the aerogel because it has alow thermal conductivity. Consider the sudden laserirradiation of (a) pure aluminum, (b) glass, and (c) aerogel. The laser provides irradiation of G = 10x10^6 W/m^2. Theabsortivities of the materials are alpha = 0.2, 0.9, and 0.8 for the aluminum, glass, andaerogel, respectively, and the initial temperature of the barrieris Ti = 300 K. Explain why the boss is concerned. Hint:All materials experience thermal expansion (or contraction), andlocal stresses that develop within a material are, to a firstapproximation, proportional to the local temperature gradient.Kglass = 1.4 W/m-KKaluminum = 237 W/m-K

Answer 1

1. for aluminium

-8438.82k/m

8.4x10³k/m

2. For glass:

-6.43x10⁶

3. For aerosol

-1.6x10⁹

Step-by-step explanation:

We have in conclusion that aerosol has a high temperature gradient. So it is not likely to have the strength to withstand a high thermal stress

Materials that have Lower thermal conductivity are likely to have their temperature gradient to be on a high side, and most of the time, these materials are brittle.

So we get why this boss is concerned about aerogel.

Please refer to the attachment for the calculations. Thank you!