Conduction heat transfer involves which of the following?

Conduction heat transfer specifically refers to the process of heat transfer that occurs through direct contact between materials. This method involves the transfer of thermal energy from one molecule to another within a solid or between a solid and a fluid when they are in direct contact.

In the context of the provided answer, when heat transfers from gas to a tube by contact, it exemplifies the conduction process. The gas molecules collide with the surface of the tube, transferring energy directly through the material of the tube via molecular interactions. This type of heat transfer is crucial in many engineering applications where components come into contact with fluids that can transfer heat effectively through conduction.

The other options specify different modes of heat transfer. For instance, heat transfer through gas motion pertains to convection, which involves the movement of fluid and heat together. Heat radiated without contact describes radiation, where energy travels through electromagnetic waves and doesn’t require a medium for transfer. Lastly, heat absorbed by water could refer to both conduction when in contact and convection when the water moves, but it does not specifically highlight the conduction process like the contact scenario does.