Heat transfer in an axially rotating tube fitted with twin twisted tapes

This paper describes an experimental study of heat transfer in an axially rotating tube fitted with twin twisted tapes. The manner in which rotation modifies the forced heat convection is considered for the case where the tube rotates about an axis in parallel to the tube's axis of symmetry with particular reference to the design of enhanced cooling channels for rotor windings in a rotating electro-machinery. A selection of experimental results illustrates the individual and interactive effects of Coriolis and centripetal buoyancy forces on heat transfer along the radially outer edge of rotating tube. With the prevailing swirl-flow structures generated by twin twisted tapes, the isolated Coriolis force effect plays a dominant role to initiate the heat transfer reduction form the static-tube scenario that is followed by a subsequent recovery which could lead to heat transfer improvement as the relative strength of Coriolis force increases. The reversed buoyancy impact from improving to impeding heat transfer develops at the higher level of Coriolis force. An empirical correlation, which is physically consistent, has been developed to permit the evaluation of interactive effects of swirling-flows, convective inertial force, Coriolis force and centripetal buoyancy on heat transfer.