Heat transfer and friction characteristics in decaying swirl flow generated by different radial guide vane swirl generators

In radial guide vane swirl generators, the flow direction must change from the radial direction to the axial direction. This can be achieved either abruptly or by means of a fairing section, and each technique can be used in conjunction with an inserted centre body (deflecting element). This research was conducted to study the effect of the geometry of the deflecting element in the radial guide vane swirl generator on the heat transfer and fluid friction characteristics in decaying swirl flow. The radial guide vane swirl generators used in this investigation had three different configurations related to the deflecting element: the swirl generator with conical deflecting element, with spherical deflecting element and with no deflecting element. These swirl generators were compared with each other by taking into account their heat transfer and friction characteristics. An augmentation up to 150% in Nusselt number relative to that of the fully developed axial flow was obtained with a constant heat flux boundary condition, depending upon the vane angles, Reynolds numbers and type of the swirl generators. It was observed that the swirl generator with no deflecting element gave the highest Nusselt numbers and also gave the highest pressure drop in both the swirl generator and the test pipe. Evaluating the effectiveness of the swirl generators for enhancing heat transfer, it was found that using the swirl generator with no deflecting element may be advantageous in terms of heat transfer enhancement and energy saving in comparison with swirl generators with a deflecting element. (C) 2002 Elsevier Science Ltd. All rights reserved.