Flow structure and heat transfer of a two-cylinder array

•Experimentally investigated how the flow structure influences heat transfer.•Flow structures were captured clearly to interpret variation of Nusselt number.•Five mechanisms of flow affecting heat transfer were identified.•Similar heat transfer mechanisms were found at lower and higher Reynolds numbers.•Staggered cylinder arrangements enhance heat transfer better than tandem ones. Two cylinders in staggered and tandem configurations were experimentally investigated to understand how the flow structure influences heat transfer. The results indicate the heat transfer of downstream cylinder exhibits more variability than that of the upstream cylinder as the stagger angle changes. The heat transfer characteristics for each flow pattern and the mechanisms governing heat transfer for the cylindrical array were clarified. Additionally, the significant effects of flow motion on the local Nusselt number of the cylinder surfaces resulting from varying stagger angles were elucidated. The overall Nusselt number in a staggered array system increases with the stagger angle, whereas in a tandem array system, it increases with the distance ratio. Notably, staggered cylinder arrangements exhibited a more pronounced enhancement in heat transfer compared to the tandem arrangement.