Heat Transfer Enhancement in a Microtube with an In-Line Package of Spherical and Inclined Oval-Trench Dimples during Transformer-Oil Pumping

Abstract

The vortex-induced intensification of the laminar (at Re = 308) flow of transformer oil and heat transfer in a microtube with an in-line package of dimples with a depth of 0.26 of the tube diameter is calculated based on the Navier–Stokes equations and the energy equation. The heat-transfer increased by nearly 20 times for eight inclined oval-trench dimples spaced around the circumference and by 13 times for spherical dimples equal in area in comparison with that for a smooth tube; moreover, the relative hydraulic losses grow by approximately 30 and 60%, respectively.