The effect of successive alternating wall deformation on the performance of an annular heat exchanger

Successive alternating wall deformations are applied to the external and internal walls of a coaxial tube. Through a numerical study, the flow structuration created by the combination of the wall deformations is investigated. The effect of the longitudinal phase-shifting between the external and internal deformations is more specifically studied by considering velocity vectors and normalised helicity fields. All the simulations are performed under the assumption of a laminar, incompressible and stationary flow. The convective heat transfer is also calculated and the performance evaluation criterion PEC=(Nu/Nu0)/(f/f0)1/3 is used to assess the thermal-hydraulic performances. For a fixed temperature condition on both walls, it is shown that the heat transfer performances are increased compared with a smooth annular geometry. The phase-shifting value giving the best thermal-hydraulic performances is also identified: a phase-shifting of one eight of a wavelength between the external and internal walls helps increasing the performances of 43%.