Heat transfer of a circular impinging jet on a circular cylinder in crossflow

• Heat transfer on a cylinder cooled by a circular impinging jet is characterized.
• Effect of a relative curvature on stagnation heat transfer is clarified.
• Flow separation causes a local heat transfer minimum on small cylinders.
• Transition from laminar to turbulent flow causes a second peak on large cylinders.

Local heat transfer characteristics on a circular cylinder subject to a circular impinging jet in crossflow are studied experimentally at a fixed jet Reynolds number of Rej = 20,000. Three cylinder-to-jet diameter ratios, D/Dj = 0.5, 2.0, and 5.0 are selected for a fixed jet diameter Dj. As reference, heat removal from a flat plate (having D/Dj = ∞) by the same circular impinging jet is also measured. Results reveal that local surface heat transfer characteristics are governed separately by the mechanisms for two limiting configurations. Smaller cylinders (than the circular jet diameter e.g., D/Dj ≤ 0.5) behave as if immersed in uniform free-stream – flow separation causes the local minimum heat transfer. Larger cylinders (than the circular jet diameter e.g., D/Dj ≥ 2.0) follow the local heat transfer characteristics observable on a flat plate subject to a circular impinging jet – laminar to turbulent flow transition induces local heat transfer peaks.