The cooling channels are preferably designed to guide a liquid cooling fluid, for example oil, water or a glycol-water mixture. However, it is also conceivable that the cooling channels are designed to guide a gaseous cooling fluid.

It is particularly preferred in the rotor assembly according to the invention if the sealing means is an O-ring. The separation portion expediently has a groove which extends in the circumferential direction and into which the O-ring is inserted.

In order to prevent the cooling fluid from escaping from the shaft it is also advantageous if the separation element has an end portion, which is arranged protruding into the interior of the shaft at a free end, wherein at least one further sealing means is provided, which seals off the end portion and the shaft with respect to one another.

In the rotor assembly according to the invention a termination element can also be provided, which seals off the second shaft portion fluid-tight at a free end opposite the first shaft portion, wherein at least one further sealing means can be provided, which seals off the termination element and the shaft with respect to one another.

A sealing means sealing off the end portion or the termination element can be an O-ring. Alternatively or additionally, the sealing means is an adhesive layer arranged on a surface of the end portion or of the termination element. The surface is particularly preferably roughened. The surface is typically the lateral surface of a substantially cylindrical part of the end portion or the termination element.