Simulations of saturated boiling heat transfer on bio-inspired two-phase heat sinks by a phase-change lattice Boltzmann method

Abstract

Pool boiling heat transfer from four types of micro-pillar heat sinks with different wettability patterns is simulated numerically with the latest version of liquid-vapor phase-change lattice Boltzmann model. Effects of pillar geometry and wettability on bubble dynamics are investigated. It is found that bubbles will nucleate either on the hydrophobic pillar top or on the hydrophilic cavity bottom between micro-pillars, depending on wettability and local wall temperature. Among the four types of micro-pillar heat sinks with hybrid wettability patterns, it is found that the bio-inspired heat sink (with hydrophobic pillar tops and hydrophilic base) has the best boiling heat transfer performance with the following desirable features: (i) unique characteristics of orderly separation of vapor and liquid paths at low superheats, (ii) hydrophobic surface characteristics where residual bubbles on hydrophobic pillar tops provide faster bubble departure frequency, (iii) triple phase lines are pinned at corners of micro-pillar, restricting expansion of bubbles into film boiling at high superheats. Simulated results show that geometry of micro-pillars and wettability patterns greatly influence transition boiling regime including the maximum heat flux (CHF) and the Leidenfrost temperature, resulting in pool boiling curves with widely different shapes.