Heat exchangers are “general industrial components for heat transfer”, and finned heat exchangers (tube-fin type / plate-fin type) are specially designed for scenarios where “one side is gas (air / flue gas / helium)”. In the server condensers, automobile radiators, central air conditioners and economizers in power plants that you are familiar with, the function of fins is to “expand the heat exchange area on the gas side” (the thermal conductivity of gas is only 1/25 that of water, so fins must be used to multiply the area).