Which type of system does not rely on mechanical means to increase heat transfer?

A passive system does not rely on mechanical means to increase heat transfer. Instead, it utilizes natural laws and phenomena, such as conduction, convection, and radiation, to facilitate heat transfer. For example, in passive solar heating systems, the design of the building and materials used are implemented to maximize solar gain, minimize heat loss, and naturally circulate air without the need for fans or pumps.

In contrast, active systems use mechanical devices, such as fans or pumps, to enhance heat transfer. Forced convection systems are a subset of active systems that specifically utilize forced air or liquid flow to improve heat transfer rates. Natural systems, while also passive, typically refer to those that use only the inherent characteristics of the environment to manage heat but are not as commonly referred to as ‘systems’ in this context. Thus, recognizing that passive systems operate without mechanical aids for heat transfer clarifies why this choice is correct.