A man strides across a bed of embers. Assume the glowing charcoal is covered wit

Question

A man strides across a bed of embers. Assume the glowing charcoal is covered with a thin layer of ash 0.50 mm thick and is at a temperature of 650C. The thermal conductiviity of ash and charcoal is 1.5 W/ (mxK). (a) Estimate the heat transferred to the feet of the walker as he traverses the embers in six quick steps. Assume the area of hte bottom of each foot comes into only 50% contact with the embers and the contact lasts 0.10seconds for each step. (b) Assume he steps onto the fire from slightly wet grass. If his feet are protected by the conversion of water from a liquid to a gas, how much water is need to carry away the heat from part a? (c) How thick would this layer of water on the sole of each foot need to be? (d) Describe what would happen if instead he were to take the same six quick steps across a slab of iron at the same temperature. If someone could help me it would be much appreciated! I am so lost. THANK YOU

Explanation / Answer

The temperature would beT=27c
=300k
a)Q=KA(T2-T1)/L=
1.5*6*0.5*(923-300)=
2803.5 J/m2
b)for 1kg water 2260 KJ are needed..for 2.8035kJ
0.00124 kg

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