Enhancing pool boiling under reduced gravity via synergistic effects of spatially non-uniform electrode and pillar-structured surfaces

In this paper, a spatially non-uniform electrode is newly designed to be coupled with non-uniformly pillar-structured surfaces for enhancing the pool boiling performance under reduced gravity. Such a novel electrode consists of a three-dimensional (3D) mesh skeleton whose part of the mesh elements are bent downward. A 3D phase-change lattice Boltzmann model with an electric field model is employed to investigate the pool boiling performance and the associated boiling enhancement mechanism. It is found that the pool boiling performance on the pillar-structured surface with a uniform electrode is related to the mesh density of the electrode, as sparse meshes limit the action region of the electric field, whereas dense meshes may block the bubble departure. However, coupling the pillar-structured surface with either the planarly or the spatially non-uniform electrodes can significantly enhance the boiling performance, and the optimum enhancement is achieved through the synergistic effects of the spatially non-uniform electrode and non-uniform surface structures, with the critical heat flux and maximum heat transfer coefficient being increased by 48.3% and 19.6%, respectively, compared with those achieved on a uniformly pillar-structured surface with a uniform electrode. The numerical results reveal that the synergistic effects can not only simultaneously expand the electric field's action region and create wide bubble departure channels but also generate a strong non-equilibrium electric force and maximize the pinching-off effect. Therefore, more rounds of bubbles are detached earlier and independently, which prevents the bubble coalescence and provides more replenishment paths of fresh liquid for boiling enhancement.