Abstract: An absorption-cycle heat pump comprises a rotary assembly including a vapor generator (GE,14), a condenser (CO,23), an absorber (AB,22), an evaporator (EV) and a solution heat exchanger (X,16). The vapor generator, the condenser and the absorber each include a wall (14, 23, 22 respectively) across which the volatile component (preferably water) and/or a liquid absorbent therefore are caused to flow under the action of the forces generated during rotation of the assembly. The evaporator comprises a plurality of finned heat exchange tubes 31 into which the volatile component is injected with a radially inwardly-directed component of motion, the tubes being of generally elliptical configuration disposed with their major axes extending generally radially.