Which surface transmits heat away from a propane container?

• A. bare metal surface
• B. wetted surface
• C. internal insulation
• D. external insulation

Answer: (B)

A wetted surface is the best way to move heat away because water on the surface acts as a powerful cooling medium. When the container’s surface is covered with water, heat from the metal conducts into the water and the water absorbs a lot of energy as it heats and especially as it boils into steam. That latent heat of vaporization removes heat rapidly, pulling heat away from the propane container and helping to keep the tank pressure down.

Bare metal would still transfer heat, but without an active cooling medium the rate is much lower. Internal or external insulation slows or reduces heat entering or leaving, but they don’t actively remove heat from the container; they’re about limiting heat transfer rather than transferring it away.