# Determine the rate of heat transfer through the window by radiation. (Round the answer to the...

## Question:

Determine the rate of heat transfer through the window by radiation. (Round the answer to the nearest whole number.) A vertical 2-m high and 5-m wide double pane window consists of two sheets of glass separated by a 3.1-cm thick air gap. In order to reduce heat transfer through the window, the air space between the two glasses is partially evaluated to 0.3 atm pressure. The emissivities of the glass surfaces are 0.48 and the glass surface temperatures across the air gap are 15C and 5C respectively. (Given {eq}k=0.02439\frac{W}{m\ {}^\circ C},\ \nu =4.753\ \mathrm{x}\mathrm{\ }{\mathrm{10}}^{-5}\frac{m^2}{s},Pr=0.7335,\ \beta =0.003534\ K^{-1} \ {/eq})

When heat is transferred from one surface to another via electromagnetic radiation, radiative heat transfer occurs. The heat energy transferred is directly proportional to the difference of the temperatures raised to the fourth power of the two surfaces. The mathematical expression for this kind of heat transfer is shown below:

{eq}\dot {Q} = \dfrac {\sigma A \left( T_1^4 - T_2^4 \right)}{\dfrac {1}{\epsilon_1} + \dfrac {1}{\epsilon_2} - 1}\\ {/eq}

Where:

A is the area of heat transfer

T is the temperature of the bodies/surfaces

{eq}\epsilon {/eq} is the emissivities of the two bodies/surfaces

{eq}\sigma {/eq} is the Stefan-Boltzmann constant which is equal to {eq}5.67 \times 10^{-8} \, \dfrac {W}{m^2K^4} {/eq} or {eq}0.1713 \times 10^{-8} \, \dfrac {Btu}{hr \cdot ft^2 \cdot R^4} {/eq}

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Given:

{eq}\sigma = 5.67 \times 10^{-8} \, \dfrac {W}{m^2K^4}\\ A = 2 \, m \times 5 \, m = 10 \, m^2\\ T_1 = 273.15 + 15 = 288.15 \, K\\ T_2 =...

Radiation, Heat Transfer & the Stefan-Boltzmann Law

from

Chapter 11 / Lesson 7
31K

After watching this lesson, you will be able to explain how radiative heat transfer works, give some real-life examples of radiation, and use the Stefan-Boltzmann Law to complete radiation calculations. A short quiz will follow.