BUOYANCY EFFECT ON LAMINAR HEAT TRANSFER IN A HORIZONTAL STRAIGHT TUBE CONTAINING A TWISTED TAPE SWIRLER

摘要

The three dimensional equations that included the buoyancy term were derived by introducing a non-orthogonal twisted cylindrical coordinate system. They were numerically solved under the condition where both the tube wall and the tape temperatures were uniform. The profiles of axial velocity and fluid temperature and the secondary flow vectors were shown. When the buoyancy is significant as well as the tape torsion effect, the peripherally averaged Nusselt number oscillates along the tube axis in the thermally developing region. The turning pitch of the tape nearly coincides with the period of the oscillation. Heat transfer is enhanced due to the twisted tape. The buoyancy further promotes it at certain portions of the axial distance, but reduces at the adjacent portions.