A heat barrier (7) is located in the region of the outlet (6) in the centre (2) of the impeller, and consists of a radial circumferential slot (8) and a first heat insulation layer installed in it. A heat insulation layer is fitted on the rear wall (11) and is functionally connected to the heat barrier. The radial circumferential slot is formed with conical or parallel side faces, and the first heat insulation layer is formed as an air layer.
