Numerical Analysis On The Characteristics Of Staggered Circular Tube Bank Fin Heat Exchanger With Fins Having Asymmetric Discontinue Annular Grooves

Tube bank fin heat exchangers are employed in a wide variety of engineeringapplications. The fins connected to tube can effectively increase the heat transfer area. Theincrease of the heat transfer area can mostly increase the capacity of heat transfer under thecircumstance of less material consumption. It is well known that when fluid flows over a tube,such as a circular tube, a separation wake zone behind the tube which is called “wake zone”will appear. Thus, the pressure drop increases and heat transfer on the fin area contacting withthe wake region declines. To reduce the size of the wake region and increase the heat transfercoefficient on the fin surface contacting with wake region is becoming a worldwide importantstudy project. Discontinue annular groove fin can mostly reduce the area of wake region.However, due to the complexity of the structure, the mechanism of heat transfer enhancementof the fin with discontinue annular grooves still is unclear. The heat transfer and fluid flowcharacteristics of the channel formed by the fins is less studied. In order to investigate themechanism of heat transfer enhancement and fluid flow characteristics of the fin withdiscontinue annular grooves, the SIMPLE program of collocated grid under body-fittedcoordinates is used to study the heat transfer and fluid flow characteristics of the fin withdiscontinue annular grooves having different asymmetricity.The role of discontinue annular grooves in guarding the fluid flow and the decrease ofthe wake region is firstly investigated. A non-dimensional parameter Se is used to specify theintensity of secondary flow which generated by discontinue annular grooves. Numerical studyis performed to investigate the local heat transfer and fluid flow characteristics of the fin withdiscontinue annular grooves with different asymmetricity. Finally, the heat transferperformance and the mechanism of heat transfer enhancement of the fin with discontinuesannular grooves are evaluated and discovered.The results show that the grooves could serve as a flow guidance to induce the fluidflowing around tube and effectively inhibit the generation of detached eddy. The groovescould interrupt the flow boundary layer to reduce its thickness by recreating new thermalboundary layers. As a result, the local heat transfer is enhanced. The grooves can inducestrong secondary flow intensity to effectively enhance heat transfer of the fin. Increasing theradial distance of the upstream grooves, in the studied range, the intensity of local secondaryflow generated by the grooves is enhanced. The overall heat transfer performance of fin iseffectively enhanced also. Decreasing the radial distance of downstream annular grooves cannot only inhibit the generation of detached eddy, but also reduce the intensity of secondaryflow. Overcoming the heat transfer enhancement on the fin surface contacting with the wakeregion, the decrease of the radial distance of downstream annular grooves has a negative effect on the heat transfer enhancement. This implies that among the functions of the grooves,boundary layer redeveloping, secondary flow enhancing, and guarding of fluid flow into thewake region, the secondary flow enhancing takes the major role to enhance the heat transferof the fin.