Abstract: A heat exchanger is disclosed, comprising a shell housing a rotor. The rotor comprises a series of hollow bodies whose interiors are hydraulically connected to each other and which are secured to a shaft which is rotatably mounted in the shell. One liquid flows through the shell in contact with the exterior of the hollow bodies. Part of the shaft is hollow to permit flow through the shaft and the hollow bodies of a second liquid. Diaphragms are disposed in the hollow bodies to regulate the flow of fluid therethrough. The shell preferably comprises large diameter fittings. The second liquid is preferably dense and may comprise sludge, waste water, etc.