A cyclic device operates between three thermal reservoirs, as shown in the figure. Heat is transferred to/from the cyclic device. It is assumed that heat transfer between each thermal reservoir and the cyclic device takes place across negligible temperature difference. Interactions between the cyclic device and the respective thermal reservoirs that are shown in the figure are all in the form of heat transfer.
The cyclic device can be
(a) a reversible heat engine
(b) a reversible heat pump or a reversible refrigeration
(c) an irreversible heat engine
(d) an irreversible heat pump or an irreversible refrigerator