Question

When an ice pack is applied to an injury, thermal energy from the injured area transfers to the ice, causing the blood vessels within the area to constrict, which reduces the swelling.

How is thermal energy transferred in this scenario?

Answer 1

Mostly by conduction. The warm tissues are in direct contact with the cold pack, so thermal energy flows by molecular collisions from skin to ice. If the ice melts it also absorbs latent heat of fusion, removing extra thermal energy. (Convection and radiation play only negligible roles here.)