The surface area of an adult human is about 1.8 m^2. Suppose a person with a skin temperature of...

Question:

The surface area of an adult human is about 1.8 m{eq}^2 {/eq}. Suppose a person with a skin temperature of {eq}34^{\circ}C {/eq} is standing nude in a room where the air is {eq}25^{\circ}C {/eq} but the walls are {eq}17^{\circ}C {/eq}. There is a "dead-air" layer next to your skin that acts as insulation.

(a) If the dead-air layer is 5.0 mm thick, what is the person's rate of heat loss by conduction?

(b) What is the person's net radiation loss to the walls? The emissivity of skin is 0.97.

(c) Does conduction or radiation contribute more to the total rate of energy loss?

(d) If the person is metabolizing food at a rate of 160 W, does the person feel comfortable, chilly, or too warm?

The rate of radiation:

The equation for the rate of radiation for any surface is equal to the product of emissivity of the surface, Stefan's constant, the surface area, and the fourth power of the absolute temperature of the object. It is given by:

{eq}\dfrac{Q}{\Delta t} = e\sigma AT^{4} {/eq}

Answer and Explanation: 1

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Given Data:

The surface area of an adult human {eq}(A) = 1.8\, \rm m^{2} {/eq}

Skin temperature {eq}(T_{s}) = 34\, \rm^{\circ}C {/eq}

Surroundi...

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Radiation, Heat Transfer & the Stefan-Boltzmann Law

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Chapter 11 / Lesson 7
34K

Learn how radiation heat transfer works and examine real-life examples of radiation heat transfer. Apply the radiation heat transfer equation known as the Stefan-Boltzmann law to calculate radiation.


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