Abstract
Ranque–Hilsch vortex tubes have the extraordinary ability to split an incoming stream of fluid into two streams—one with a lower absolute total temperature than the incoming flow and the other with greater total temperature. The physical mechanism involves inducing an intense swirl of the flow down the length of the tube. The warmer flow exits around the periphery at the end of the tube, while the cooler central flow changes direction within the core and exits the opposite end. While much research has focused on the physical mechanisms of the energy separation, relatively little attention has been paid to the heat transfer behavior should a heat flux be applied to the walls. In the present work, experiments were performed using a vortex tube with air and varying levels of heat addition, up to approximately 15 kW/m2. Companion computational experiments were performed that allowed the determination of axially resolved Nusselt number distributions, the first of their kind for vortex tube flows. A notable finding is that the vast majority of heat added to the vortex tube flow remains within the hot stream; i.e., the cold stream experiences relatively little temperature rise due to the heat addition. For example, even when only 30% of the flow exits the hot side of the tube, it retains more than 80% of the heat added to the flow. Additionally, a modified swirl number was also defined that was found to scale the Nusselt number augmentation across the two different total flowrates examined presently.
