The influence of axial flow on the fluid dynamics and heat transfer in decaying, swirling flow in a pipe

Engineering equipment can be designed to utilize swirling flows to increase heat transfer rates. The present experimental study provided a holistic view of decaying swirling flow in a long, constant diameter pipe. The swirling flow was generated using a tangential injection mechanism. The two inlet boundary conditions were tangential flow and superimposed tangential and axial flow. This study documented how superimposing axial flow on tangential flow influences the spatial flow structure, the velocity field, the local heat transfer rates, and the temperature field.; Documentation of the axial and lateral velocity fields using a full field measurement method was achieved using a novel particle image velocimetry technique developed specifically for swirling flows. Profiles of axial velocity for the tangential flow inlet condition showed that a reversed flow region was located near the axis of the pipe. The reversed flow region extended from the inlet to the outlet of the pipe. For superimposed tangential and axial flow, the existence of a velocity deficit region depended upon the design swirl intensity. The maximum normalized azimuthal velocity decreased exponentially in the axial direction. The magnitude of the normalized azimuthal velocity was primarily dependent upon the design swirl intensity. Flow visualization, axial velocity field, and lateral velocity results showed that the flow field was asymmetric.; For tangential flow, the radial profiles of fluid temperature showed that warm fluid was transported from the pipe wall to the center of the pipe then transported upstream in the reversed flow region of the flow. The radial profiles of fluid temperature for the tangential flow had a local maximum located near the pipe axis. For superimposed tangential and axial flow, the radial profiles of fluid temperature were relatively flat and asymmetric.; The local Nusselt numbers were greater than that for fully developed flow and for thermally developing flow. The maximum local Nusselt number was located near the pipe inlet and decreased in the axial direction. The value of the local Nusselt number near the pipe outlet was larger than the fully-developed value. Increasing the design swirl intensity caused the values of the local Nusselt numbers to increase.