Heat transfer device

A heat transfer device comprising an inner tube mounted within a hollow tubular chamber of a heat exchanger, the hollow tubular chamber having a closed end that has concave or inwardly sloping inner surfaces and the inner tube having an open end that terminates short of the closed end of the tubular chamber, wherein a diffuser is provided around a section of the inner tube adjacent its open end, the diffuser being shaped such that an operatively front part of the diffuser substantially conforms to a shape of the inner surfaces of the closed end of the hollow tubular chamber so as to form a narrow flow passageway between the diffuser and the inner surfaces at the closed end, and an operatively back part of the diffuser slopes or transitions towards the inner tube and away from its open end to form a diffusion zone in the hollow tubular chamber, wherein a working fluid moves through the inner tube to exit its open end, impinges on the closed end of the tubular chamber, is directed through the narrow flow passageway and undergoes pressure recovery in the diffusion zone.