A person with estimated surface area of 20 ft 2 and effective surface temperatur

Question

A person with estimated surface area of 20 ft2 and effective surface temperature (including clothing) of 84 °F is standing in a room where the walls, ceiling, and floor are all at 68 °F. If the emissivity of the person is 0.8, what is the radiation heat transfer (BTU/hr) from the person to the room surfaces?

Hint 1: Use equation for radiation exchange where total radiation leaving one surface (floor) is intercepted by another surface (walls and ceiling - since all are at same temperature). What is the shape factor in this case?

Hint 2: Use Kirchhoff's identity to find absorptivity. Use radiation balance (absorptivity, reflectivity, transmissivity) on a surface to find reflectivity values.

Hint 3: Simplify the third term in the denominator of the radiation exchange equation by realizing for this application that A1<< A2 (A1 is much smaller than A2).

Explanation / Answer

net hear radiation transfer q = (Th4 - Tc4) Ac

=0.8 given

Th = 84  oF

Tc= 64 oF

= tefan-Boltzmann Constant = 1.714 x10-9 ( Btu/(h ft2oR4) )

AC= 20 ft2

q = 0.8 *1.714 10-9*(844 -644 )20 = 0.9052 BTU/hr

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.