Surface-active ionic liquids as potential additive for pool boiling based energy systems

Abstract

Thermal devices relying on liquid-vapor phase change processes such as boiling and condensation are ubiquitous. They utilize latent heat of vaporization of fluid to facilitate heat transfer at significantly smaller temperature budgets. The resulting high heat transfer coefficient (HTC) minimizes irreversibility to enable high efficiency in comparison to single-phase heat transfer. However, ever-increasing global energy demands continue the quest for further improvement in efficiency of two-phase energy conversion and heat rejection devices. In this regard, the addition of surfactants in boiling fluid is a widely used HTC enhancement technique. However, the high HTC with surfactants is usually accompanied by a deterioration in critical heat flux (CHF), followed by a premature thermal runaway due to the transition to low HTC film boiling regime. Such a low ceiling on heat dissipation limits the implementation of this strategy to low power density devices. Here we perform near-saturated pool boiling experiments to present surface-active ionic liquids (SAILs) as potential additives for boiling based energy systems. We investigate the parametric effect of SAIL type and concentration on HTC and CHF. Simultaneous enhancement in both, the HTC (≈46%) and the CHF (≈53 %) in comparison to boiling with a typical surfactant additive is reported. This result is encouraging and suggests that SAILs can replace surfactants as additives to enable efficient energy conversion and heat rejection in high power density devices.