An overview of heat transfer enhancement methods and new perspectives: Focus on active methods using electroactive materials

The main techniques for the enhancement of heat transfer between a solid wall and a fluid are reviewed for both single phase (liquid and gas) and two-phase (boiling and condensation) systems. First, a brief description of the commonly used passive techniques is given. For each of them, we report the values of the enhancement factor given in the literature. The principal active methods, i.e. methods involving the supply of external energy, are then detailed. The physical mechanisms leading to heat transfer enhancement are identified from the analyses published to date. The paper then focuses on the techniques that use periodic deformation of a wall over time. Such a wall deformation enhances heat transfer by disrupting the boundary layer and simultaneously setting the fluid in motion. The piezoelectric materials that can be implemented to generate the channel wall dynamic deformation are reviewed. As deformation of a wall is generally of low amplitude, the technique is well suited to micro channel systems: (i) in single-phase configuration, imposing a deformation traveling wave to a micro channel wall is found to simultaneously enhance heat transfer and set in motion the fluid; (ii) boiling in a narrow space is found to involve both boiling and cavitation phenomena in the nucleation process.