Which process does NOT involve the transfer of thermal energy?

The process that does not involve the transfer of thermal energy is refraction. Refraction occurs when a wave, such as light or sound, changes its speed and direction as it passes from one medium to another. This bending of the wave results from changes in the wave's speed due to the different properties of the materials it is traveling through, but it does not inherently involve the transfer of thermal energy.

In contrast, conduction is the transfer of thermal energy through direct contact between particles, typically in solids. Convection involves the transfer of thermal energy through the movement of fluids (liquids or gases) as warmer areas of the fluid rise and cooler areas sink. Thermal radiation is the transfer of energy through electromagnetic waves and can occur in a vacuum. Thus, refraction stands out as a process focused on wave properties rather than thermal energy transfer.