Investigation of heat transfer performance within annular geometries with swirl-inducing fins using clove-treated graphene nanoplatelet colloidal suspension

Abstract

The paper investigated the benefits of having fins that induce swirling flow within an annular passage. The importance of the vortical structures produced using different fin angles and flow velocities in heat transfer was studied. The combination of swirling fluid with recirculation on heat transfer within an annular domain was not fully understood, and this paper aims to address that gap. The 10°, 20°, 30° and 40° angled fins were investigated to understand the changes in heat transfer performance as fluid recirculation becomes more dominant as angles become steeper. The usage of CGNP colloidal suspension was investigated for its potential benefits in heat transfer in a domain with angled fins. The CGNP concentrations of 0.025, 0.075 and 0.1 mass % were used as part of this investigation. Higher concentrations of CGNP increased the overall heat transfer coefficient. A more compact fin spacing improved heat transfer performance at the expense of increased pressure drop. Fin angles of 20° and 30° yielded poor heat transfer performance in the transitional flow regime (2000 < Re < 3000) due to the smaller swirling longitudinal vortices being insufficient in promoting fluid mixing from the thermal boundary layer into the freestream.

The Effect of Angled Fins in Generating Swirling Flows with Vortices That Augment Heat Transfer Performance in an Annular Conduit

“…This indicates that this type of vortex improves heat transfer performance with minimal impact on pressure drop, thus resulting in significantly higher PEC values. This finding expands on the initial finding on longitudinal vortices and their role in improving heat transfer by Nair et al [25], where they found that heat transfer improved when the longitudinal vortex generated by the angled fins was large enough to mix the heated fluid from the thermal boundary layer into the faster-flowing freestream region. In terms of pure improvement to heat transfer, the transverse vortex also appears to contribute meaningfully, as evidenced by the excellent improvement in Nu over the baseline case in Figure 8.…”

“…This study enhances the initial investigation by Nair et al [25], where angled fins, which encourage swirling flow, were investigated for heat transfer. The swirling nature of the flow when the appropriate fin angles were used, combined with the contribution of the longitudinal and transverse vortices, provided excellent overall improvement in terms of PEC.…”

“…Instead, the author is aimed at identifying the optimal degree of twist for the tape in terms of the number of turns per unit length. In a recent study, Nair et al [25] found a correlation between the size of the longitudinal vortex and the enhancement in heat transfer performance. This theory was later presented by Wang et al [26], where cooler surface temperatures were reported on locations where strong and large vortices appeared, regardless if transverse or longitudinal.…”

“…As a result, this study will observe the behaviour of the generated vortices when the gap between the fin tip and the outer wall varies. Such studies on angled fins within an annular conduit have yet to be conducted aside from a preliminary study by Nair et al [25,29].…”

Thermohydraulic and Irreversibility Analyses of Swirl Flows Utilizing Distorted Radial Fins: Entropy Generation and Entransy Dissipation Evaluation

“…Longitudinal vortices rotate perpendicular to the flow direction, whilst transverse vortices rotate parallel to the flow direction. The creation of such vortical structures has shown immense improvements in heat transfer enhancement, due to various ideal flow characteristics induced in the flow [6][7][8][9][10]. In spite of the enhanced heat transfer rates, the presence of fins often leads to increased pressure drop and friction losses across the system, which correlates to higher pumping power requirements [11].…”