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Difficulty: MediumHeat Transfer: Radiation

A double-walled cryogenic storage vessel uses a vacuum gap between its inner and outer steel walls to keep the contents cold. While the vacuum effectively stops conduction and convection, thermal energy can still cross the empty space. Which of the following surface treatments on the walls facing the vacuum gap would most effectively reduce this remaining heat transfer?

  1. Applying a highly polished, reflective metallic finishAnswer
  2. B
    Painting the surfaces with a flat black coating
  3. C
    Installing solid metal struts between the walls to draw heat away
  4. D
    Creating a rough, textured surface to disrupt convective air currents

Answer

Applying a highly polished, reflective metallic finish
In a vacuum, the only possible method of heat transfer is thermal radiation (electromagnetic waves). A highly polished, reflective surface acts like a mirror for infrared radiation, bouncing the heat waves back and preventing them from being absorbed into the inner wall of the vessel.

Step-by-Step Solution

1
Identify the remaining mode of heat transfer across the vacuum.
Thermal radiation is the only mode of heat transfer that can travel through empty space (a vacuum), as it relies on electromagnetic waves rather than a physical medium.
Conduction and convection require matter (solids, liquids, or gases) to transfer heat.
2
Determine how to minimize thermal radiation.
Radiation is minimized when surfaces have low emissivity and high reflectivity.
Highly polished, light-colored, or shiny metallic surfaces reflect infrared waves instead of absorbing or radiating them.

Key Concept

Heat Transfer: Radiation
Estimated Time:1m 0s
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Topics

Heat Transfer: Radiation

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