Rotary heat exchangers can include a ride-along compressor, at least a portion of which can be rotated along with the heat exchanger. By rotating at least a portion of the compressor along with the heat exchanger, a sealed fluid circuit containing a two-phase working fluid can be provided. A rotary heat pump or heat engine can include an evaporator and a condenser in the form of back-to-back centrifugal fans. The centrifugal fan blades or other portions of the evaporator and condenser may include internal cavities where the working fluid undergoes a phase change.