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Question

Difficulty: EasyHeat Transfer: Radiation

A technician places two identical steel tanks outdoors in direct sunlight. Tank X is painted flat black, while Tank Y is painted glossy white. After a few hours, Tank X is significantly hotter to the touch than Tank Y. What is the primary reason for this temperature difference?

  1. Flat black surfaces are better absorbers of thermal radiation than glossy white surfaces.Answer
  2. B
    Glossy white surfaces restrict the thermal convection of the surrounding air.
  3. C
    Flat black paint increases the specific heat capacity of the steel tank.
  4. D
    Glossy white paint prevents the direct conduction of heat from the sun.

Answer

Flat black surfaces are better absorbers of thermal radiation than glossy white surfaces.
The correct answer accurately states that flat black surfaces are better absorbers of thermal radiation. Heat from the sun travels as electromagnetic radiation. Dark, matte finishes absorb most of this radiant energy and convert it into heat, whereas light, glossy finishes reflect most of the radiant energy away.

Step-by-Step Solution

1
Identify the source and method of heat transfer.
The sun heats the tanks through the vacuum of space, meaning the heat transfer method must be thermal radiation.
Conduction requires direct contact, and convection requires a fluid medium, leaving radiation as the only way solar energy reaches the tanks.
2
Analyze how the different surface finishes interact with thermal radiation.
The flat black tank (Tank X) absorbs more radiant energy, while the glossy white tank (Tank Y) reflects more of it.
Dark, matte surfaces are excellent absorbers of electromagnetic radiation, whereas light, shiny surfaces are excellent reflectors.

Key Concept

Thermal radiation absorption depends heavily on an object's surface color and texture.
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Topics

Heat Transfer: Radiation

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