A system that does not use fans or pumps for heat transfer is referred to as?

In the context of heat transfer, a system that does not rely on fans or pumps is known as a passive system. Passive systems utilize natural processes for heat exchange, such as conduction, convection, and radiation, without the assistance of mechanical devices. These systems often take advantage of the natural movement of air and thermal differentials, promoting efficiency by allowing heat to move without the need for active mechanical components.

For example, a passive solar heating system captures sunlight and uses it to warm a space directly through building design, positioning of windows, and materials that absorb and store heat. This contrasts with active systems, which do require powered devices to facilitate heat movement or transfer.

In the context of the other choices, a forced system specifically utilizes mechanical means, like fans or pumps, to move air or fluids, thereby contradicting the definition of a passive system. An active system also involves mechanical methods for manipulation of heat transfer, while a closed system refers to a thermodynamic system where mass does not enter or leave the system boundaries but can exchange energy, which is again distinct from the definition of a passive system.