Why are fins used in heat transfer applications?

Fins are extended surfaces used to increase the heat transfer rate by expanding the surface area available for convection. They are particularly effective when one fluid has a much lower heat transfer coefficient than the other (e.g., air vs. liquid). Common applications include air-cooled engines, electronic heat sinks, radiators, and air conditioning condensers. The effectiveness of fins depends on their geometry, material thermal conductivity, and the convective environment. High-conductivity materials like aluminum and copper are preferred for fin construction.