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Energy Transfer in Thermal and Fluid Systems

Problem: An oven door consists of a layer of asbestos sandwiched between a layer of steel on the inner surface and a layer of wood on the outer face. The thickness of the steel is 20mm and that of the wood 12mm. The adhesive used to bond the wood to the asbestos has a maximum safe working temperature of 93 degrees C(when bonded to the wood). The temperature of the inside surface of the door is 537 degrees C and that of the outside 15.5 degrees C. Determine the minimum allowable thickness of asbestos, ignoring the thickness and resistance of the adhesive.

Assue the following thermal conductivities:

k-steel = 41.5W/mK, k-asbestos = 0.19w/mK, k-wood = 1.9 W/mK

Not sure how to approach the question. Where do I begin?

Solution Preview

By Fourier's law:
qx" = -k dT/dx
Now we have for all three materials:
qx" = ...

Solution Summary

Solution includes formula's and calculations and directions for solving for he minimum width of the asbestos.