Enhanced heat transfer in a microchannel with pseudo-roughness induced by Onsager-Wien effect

A three-dimensional numerical analysis of flow and conjugate heat transfer in a microchannel in the presence of the electric-field-induced Onsager–Wien effect is performed. A novel design is proposed to induce a pseudo-roughness effect in the microchannel and thereby increasing the heat transfer. A series of thin plate electrode pairs are flushed along the bottom wall of the microchannel. The electric-field-enhanced dissociation of ions induces the Onsager–Wien effect, and generates small flow vortices near the bottom wall of the channel. These flow vortices with sharp local velocity gradients effectively disrupt the viscous and thermal boundary layers, and thus, introduce a pseudo-roughness effect. This disruption of the boundary layers improves the heat transfer between the channel wall and the working fluid. The thermal and hydraulic performances in the microchannel are quantified as a function of the flow Reynolds number Re and electric Reynolds number Re_EL. In general, the performance factor PF is higher when the flow and electric Reynolds numbers are higher. However, the associated pressure drop penalty reduces the PF PF<1 in viscous-effect-dominated flows at Re=250. By contrast, the Onsager–Wien effect increases the PF to a maximum value of 1.26 in inertia-dominated flows at Re=1000 and Re_EL=15. A significant heat transfer enhancement is realized, even at a low applied voltage of ∼1 kV. The results of this study indicate that the pseudo-roughness produced by the electric-field-induced Onsager–Wien effect can substantially enhance the heat transfer in a microchannel with a trivial amount of additional power consumption. Results presented in this study will serve as a benchmark to design microchannels with enhanced heat transfer by using active vortex generation based on Onsager-Wien effect.