All condensers operate by removing heat from the gas or vapour; once sufficient heat is eliminated, liquefaction occurs. For some applications, all that is necessary is to pass the gas through a long tube (usually arranged in a coil or other compact shape) to permit heat to escape into the surrounding air. A heat-conductive metal, such as copper, is commonly used to transport the vapour. A condenser’s efficiency is often enhanced by attaching fins (i.e., flat sheets of conductive metal) to the tubing to accelerate heat removal. Commonly, such condensers employ fans to force air through the fins and carry the heat away. In many cases, large condensers for industrial applications use water or some other liquid in place of air to achieve heat removal.