A micro-wire of diameter 10.0 µm = 10.0×10-6 m is carrying an electrical current, and the wire will get hot when current is flowing through it. Normally insulation might be used to keep the heat IN the wire, but here we want to add insulation to actually INCREASE the heat LOSS from the wire! The wire is made of copper, and we will use a special coating process to insulate the wire with a layer of silica aerogel (properties in Pitts & Sissom book). The ambient air temperature is Tout = 24 C. The heat transfer coefficient is hout = 19 W/m2-C. What is the "critical thickness" of insulation, such that if the layer were any thinner, the insulation would actually cause the heat flux to increase?
a) Any thickness of insulation will decrease heat loss for this problem.
b) 1.26 mm
c) 20.3 m
d) 3.61 cm
e) 2.13 cm