Name: radiation heat transfer and thermographs
Uploaded: 2023-09-18T17:11:17.000Z
Duration: 1 min 5 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Place in the Universe

ESS.EES.1.4

Absorption of Radiation

The rate of heat transfer through radiation is given by the Stefan-Boltzmann law of radiation, which needs a correction when a radiating body is also absorbing radiation from its surroundings.
Consider a body at temperature T1 radiating heat in the atmosphere.
Simultaneously, another body at temperature T2, placed near the first body, is also emitting heat.
In this situation, the first body, along with radiating, also starts absorbing heat. The rate of heat absorbed by the first body can be given in terms of the temperature of the surrounding body.
So, the net rate of radiation from the first body can be evaluated by finding the difference between the heat radiated and the heat absorbed; this gives a refined equation for the Stefan-Boltzmann law of radiation.
If the value of the net radiation rate is positive, it implies that the heat transfer is taking place from the first body to its surrounding body.

absorption of radiation

The rate of heat transfer by emitted radiation is described by the Stefan-Boltzmann law of radiation:
<img alt="Stefan-Boltzmann law equation diagram, P=σAeT^4, for thermal radiation study." src="/files/ftp_upload/14165/14165_equation_1.svg" style="text-align: center; height: 20px;" data-altupdatedat="1761830439000" data-alt="Equation1">
where σ is the Stefan-Boltzmann constant, a combination of fundamental constants of nature; A is the surface area of the object; and T is its temperature in kelvins.
The proportionality to the fourth power of the absolute temperature gives a remarkably strong temperature dependence. It allows the detection of even small temperature variations. Images called thermographs can be used medically to detect regions of abnormally high temperature in the body, which can be indicative of disease. Similar techniques can be used to detect heat leaks in homes, optimize the performance of blast furnaces, improve comfort levels in work environments, and even remotely map the Earth's temperature profile.
The Stefan-Boltzmann equation needs only slight refinement to deal with a simple case of an object's absorption of radiation from its surroundings. Assuming that an object with a temperature T1 is surrounded by an environment with uniform temperature T2, the net rate of heat transfer by radiation is as follows:
<img alt="Thermal radiation heat transfer formula, P_net=σAe(T₂⁴-T₁⁴), equation for energy exchange." src="/files/ftp_upload/14165/14165_equation_2.svg" style="text-align: center; height: 25px;" data-altupdatedat="1761830439000" data-alt="Equation2">
where e is the emissivity of the object alone. In other words, it does not matter whether the surroundings are white, gray, or black; the balance of radiation into and out of the object depend on how well it emits and absorbs radiation. When T2 &gt; T1, the quantity Pnet is positive, meaning the net heat transfer is from hot to cold.

The rate of heat transfer by emitted radiation is described by the Stefan-Boltzmann law of radiation:

where &#963; is the Stefan-Boltzmann constant, a ...

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JoVE Core

Physics

Unit 1

Temperature and Heat

KEY TERMS AND CONCEPTS

radiation heat transfer and thermographs

Radiation heat transfer depends on temperature, surface area, and emissivity. The Stefan-Boltzmann law describes the rate of heat transfer by emitted radiation. In this law, σ is the Stefan-Boltzmann constant, A is the object’s surface area, and T is its temperature in kelvins.

The fourth-power dependence on absolute temperature makes radiation highly sensitive to small temperature changes. Even a slight rise in temperature can change the emitted heat a lot. That sensitivity is why radiation can reveal small temperature differences.

Thermographs are images used to show these temperature differences. In medicine, they can help detect regions of abnormally high temperature in the body, which may point to disease. Similar methods can also help find heat leaks in homes, improve blast furnace performance, increase comfort in work spaces, and map Earth’s temperature from a distance.

The same radiation idea also applies when an object absorbs heat from its surroundings. For a body at temperature T1 in an environment at uniform temperature T2, the Stefan-Boltzmann equation is adjusted slightly to find the net rate of heat transfer. The emissivity, e, belongs to the object itself. The color of the surroundings does not matter; what matters is how well the object emits and absorbs radiation. When T2 is greater than T1, Pnet is positive, so the net heat flow is from hot to cold.

Radiation Heat Transfer and Thermographs

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Radiation heat transfer depends on temperature, surface area, and emissivity. The Stefan-Boltzmann law describes the rate of heat transfer by emitted radiation. In this law, σ is the Stefan-Boltzmann constant, A is the object’s surface area, and T is its temperature in kelvins. The fourth-power dependence on absolute temperature makes radiation highly sensitive to small temperature changes. Even a slight rise in temperature can change the emitted heat a lot. That sensitivity is why radiation...

key terms and concepts

Learn how the Stefan-Boltzmann law links radiation heat transfer to temperature, and how thermographs detect heat differences in medicine and other uses.

Radiation Heat Transfer and Thermographs | JoVE K12

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Pennsylvania State Academic Standards

Physical Science

Waves and Electromagnetic Radiation

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High School

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Earth’s Systems

HS-ESS2-4

Waves And Their Applications

HS-PS4-4

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Ohio’s Learning Standards and Model Curriculum

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Minnesota Academic Standards in Science

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112.49.c.8.

112.49.c.8.A.

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Earth and Space Science

9-12.ESS.1.2.e

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Earth’s Place in the Universe

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SC.912.P.10

SC.912.P.10.4

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Radiation Heat Transfer and Thermographs

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