Heat Transfer in an Axially Rotating Tube Fitted with twin Twisted Tapes

Abstract

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.

Turbulent heat transfer and pressure drop in tube fitted with serrated twisted tape

“…The different Nu and f enhancement ratios between the laminar and turbulent flows in a tube with twisted tape insert, as reported in [8,11], are caused by the different plain-tube Nu and f references selected for laminar and turbulent flows. Further improvements of thermal performance for a duct with twisted tape insert are continued when attempting to use the regularly spaced twisted tape elements [13,14], the combination of spirally corrugated tubes with a continuous twisted tape [15,16], the twisted tape insert in a square duct [17,18] and the insertion of multiple twisted tapes in a tube [19,20]. The research goals [13][14][15][16][17][18][19][20] involve the further increase of HTE ratio and thermal performance factor with the extended effective Re range.…”

“…Further improvements of thermal performance for a duct with twisted tape insert are continued when attempting to use the regularly spaced twisted tape elements [13,14], the combination of spirally corrugated tubes with a continuous twisted tape [15,16], the twisted tape insert in a square duct [17,18] and the insertion of multiple twisted tapes in a tube [19,20]. The research goals [13][14][15][16][17][18][19][20] involve the further increase of HTE ratio and thermal performance factor with the extended effective Re range. In a tube fitted with regularly spaced twisted tape elements connected by a circular rod, the pressure drop could be reduced by up to 40% of that found in the tube with fulllength twisted tape insert without impairing its heat transfer rate [13,14].…”

Effect of Twisted Tapes Insert on Heat Transfer and Pressure Drop Augmentation for High Viscous Fluids inside Rotating Tubes

“…They found that, as the tape length decreases, both friction factor and Nu decrease. An experimental study of heat transfer in an axially rotating tube fitted with twin twisted tapes was performed by Chang et al [4] to unravel the effect of rotation on heat transfer performance. The rotating speed was in range of 0 -1000 rpm and Re = 5000, 75000, 10000, 12500 and 15000.…”