Abstract: A heat transfer device (100) includes an inner tube (102) mounted within a tubular chamber (104) of a heat exchanger (106). The hollow tubular chamber (104) has a closed end (108) with inwardly sloping inner surfaces (110) and the inner tube (102) has an open end (112) that terminates short of the closed end (108). A diffuser (114) is provided and is shaped such that an operatively front part (116) thereof substantially conforms to a shape of the inner surfaces (110) of the closed end (108) so as to form a narrow flow passageway (118) between the diffuser (114) and the inner surfaces (110) at the closed end (108), and an operatively back part (120) of the diffuser (114) slopes towards the inner tube (102) and away from its open end (112) to form a diffusion zone (122). Heat transfer assemblies utilising the heat transfer device (100) are also disclosed.