The assembly has a heat transfer device comprising a cladding tube (2) e.g. steel tube and a heat transfer element (3), is inserted in a container (1). A heater (5) is inserted into a cladding tube with a gap (4) formed as portion of heat transfer device. The gap is filled with highly heat conductive medium e.g. graphite powder that is air-tight and pressure-tight form-fitting. A centering unit (7) is provided for replacing heater with new heater, without impairing heat transfer element which is removed from the cladding tube without damage. The heat transfer element is made of aluminum.
