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

Abstract

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 ( 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 ( 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 ( 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 ( 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 ( β), the director diameter ( d), and with decrease in the CITSG angle ( α). Likewise, variation of Nu PR and Nu ER is also essentially similar for the same independent parameters.