Abstract: A heating device (124) for heating particles to be freeze-dried in a rotary drum (102) of a freeze-dryer (100) is provided, the device comprising at least one radiation emitter (202) for applying radiation heat to the particles, and a tube-shaped separator (204) for separating the particles from the at least one emitter (202). The separator (202) being integrally closed at one end and separating an emitter volume (206) encompassing the at least one emitter (202) from a drum process volume (126) inside the drum (102), wherein the heating device (124) protrudes into the drum process volume (126) such that said integrally closed end of the separator (204) is arranged inside the drum (102) as a free end.