Review of confined swirling flows and bluff body impacts on flow and heat transfer characteristics

Confined swirling flows are central to different industrial processes such as phase separation, heat exchange and flow stabilization. Hence, there have been numerous studies that have investigated swirling flows in a confined geometry. Although the research focus of these types of flows have been significantly on combusting flows in the past, critical research findings have emerged in cold swirling flow in both vertical and horizontal pipe orientation that are essential to further research developments in these type of flows in the last decade. For example, the measurements of the swirl length and decay in two phase fluid flows is critical to the operation of commercial heat exchanger and phase separators. However, studies on the swirl length and decay for two phase flows have received significantly little attention until recently. Currently, experimental and modeling studies have been reported for the determination of these swirl parameters. Likewise, further progress could be observed in the characterization of vertical cold swirling flow transition benchmark with the void fraction, as well as new finding in tangential conduit phase separation in vertical flows which were hitherto rare. The utilization of horizontal swirling flow in oil-water separation as well as novel investigation of the impact of bluff bodies on the swirling flow characteristics have been recently examined as well. Consequently, in this review, the developments in swirling confined non-reacting flows with and without bluff bodies are discussed. Developments in the characterization of vertical swirling two phase flow patterns and transition, development of swirl decay laws for two phase swirling flow with and without interfacial frictional force, report of new separation design such as the narrow tangential conduit and the assessment of two-phase swirling flows which are influenced by surfactants are evaluated. Moreover, advancements in oil-water swirling flows studies are reported. The main findings in the oil studies include the demulsification of white oil-water mixture using a novel axial vertical and horizontal flow inline separator, the optimization and enhancement of the design of swirling flow based demulsification separators and the investigation of the path, coalescence, and disintegration of oil droplets in water continuous phase. The utilization of bluff bodies such as sphere, cone, circular disk, cuboid, diamond and trapezium are explored. Finally, the future outlook in swirling confined flow studies is highlighted.