Convective heat transfer increase in internal laminar flow using a vibrating surface

• Experimental tests were performed on water laminar boundary layer.
• Small pressure disturbances were used to increase the convective heat transfer.
• The convective heat transfer was evaluated on an instrumented heated pin-fin.
• A linear relation between disturbance frequencies and Reynolds number was found.
• A maximum Nusselt enhancement of 9.33% was found.

Laminar to turbulent transition is a very complex phenomenon, where instability waves are able to grow inside the fluid boundary layer. According to the receptivity theory, only some perturbations with particular frequencies are able to induce those instability waves. The aim of this paper is to find a new way to increase the convective heat transfer by a locally promotion of those instability waves. This is obtained with the introduction in a laminar water flow of small pressure disturbances in a laminar water flow. Experiments have been performed in a close circuit water tunnel. A stack of two piezo-ceramic actuators (M.E.M.S.) has been used to induce vibration on a circular surface located on the tunnel floor. The vibration effect has been evaluated by monitoring the heat transfer coefficient on a heated circular pin-fin. The pin has been positioned downstream of the vibrating surface and equipped with calibrated thermocouples. Tests have been performed at different Reynolds numbers, pressures and water temperatures. The results have showed an increase in Nusselt number of up to 9.33%. Flow visualizations with dye have been reported to better understand the phenomenon.