PURPOSE: To improve cleaning effect and save an injection medium and an injecting time by a method wherein some thermal conducting elements divided at a plane perpendicular to a rotary shaft are arranged around the rotary shaft, an injection pipe is arranged between the thermal conducting elements and the pipe is made to communicate with a fluid passage arranged at a central part of the rotary shaft.

CONSTITUTION: An injecting pipe 19 having a fluid injection hole 18 is arranged at an intermediate part of thermal conducting elements 4, 5 and 6 of each of layers. With this arrangement, an interface part between a low temperature element 4 and a medium temperature element 5, an interface part between the medium temperature element 5 and the hot temperature element 6 and a central part of the thermal conducting element 3 from each of both end surfaces are easily and easily cleaned. If each of communicating pipes 21 of injected medium is independently arranged, only the minimum required location can be cleaned. Further, a changing-over of the communicating pipe 21 enables several kinds of injection media can be utilized. In this way, an efficient and effective cleaning is carried out under a cleaning of an inner surface of each of the layers in the thermal conducting elements 3.