A process of transferring heat from a first relatively cold medium to a second relatively hot medium features rotating a contained amount of a compressible fluid about an axis of rotation, thus generating a radial temperature gradient in the fluid, and heating the second medium by the fluid in a section of the fluid relatively far from the axis of rotation. An apparatus for carrying out the process includes a gastight drum rotatably mounted in a frame, and a first heat exchanger mounted inside the drum relatively far from the axis of rotation of the drum.