Heat transfer augmentation by swirl generators inserted into a tube with constant heat flux

A novel conical injector type swirl generator (CITSG) is devised in this study. Performances of heat transfer and pressure drop in a pipe with the CITSG are experimentally examined for the CITSGs' angle (alpha) of 30 degrees, 45 degrees and 60 degrees in Reynolds number (Re) range of 10,000-35,000. Moreover, circular holes with different numbers (N) and cross-section areas (A(h)) are drilled on the CITSG. In this way, total areas (A(t) = N . A(h)) of the holes on the CITSG are equaled each other. Besides, flow directors having three different angles (beta = 30 degrees, 60 degrees and 90 degrees) to radial direction are attached to every one of the holes. This study is a typical example for decaying flow. All experiments were conduced with air accordingly; Prandtl number was approximately fixed at 0.71. The local Nusselt number (Nu(x)), heat transfer enhancement ratio (Nu(ER)) and heat transfer performance ratio (Nu(PR)) are calculated and discussed in this paper. It is found that the Nu(ER) decreases with increase in Reynolds number, the director angle (beta), the director diameter (d), and with decrease in the CITSG angle (alpha). Likewise, variation of Nu(PR) and Nu(ER) is also essentially similar for the same independent parameters. (C) 2009 Elsevier Ltd. All rights reserved.