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 CITSGsʹ angle (α) of 30°, 45° and 60° in Reynolds number (Re) range of 10,000–35,000. Moreover, circular holes with different numbers (N) and cross-section areas (Ah) are drilled on the CITSG. In this way, total areas (At = N · Ah) of the holes on the CITSG are equaled each other. Besides, flow directors having three different angles (β = 30°, 60° and 90°) 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 (Nux), heat transfer enhancement ratio (NuER) and heat transfer performance ratio (NuPR) are calculated and discussed in this paper. It is found that the NuER decreases with increase in Reynolds number, the director angle (β), the director diameter (d), and with decrease in the CITSG angle (α). Likewise, variation of NuPR and NuER is also essentially similar for the same independent parameters.