High Heat Flux Evaporation of Low Surface Tension Liquids from Nanoporous Membranes

Abstract

Water is often considered as the highest performance working fluid for liquid–vapor phase change due to its high thermal conductivity and large enthalpy of vaporization. However, a wide range of industrial systems require using low surface tension liquids where heat transfer enhancement has proved challenging for boiling and evaporation. Here, we enable a new paradigm of phase change heat transfer, which favors high volatility, low surface tension liquids rather than water. We utilized a nanoporous membrane of ≈600 nm thickness and <140 nm pore diameters supported on efficient liquid supply architectures, decoupling capillary pumping from viscous loss. Proof-of-concept devices were microfabricated and tested in a custom-built environmental chamber. We used R245fa, pentane, methanol, isopropyl alcohol, and water as working fluids with devices of total membrane area varying from 0.017 to 0.424 cm2. We realized a device-level pure evaporation heat flux of 144 ± 6 W/cm2 for water, and the highest evaporation heat flux was obtained with pentane at 550 ± 90 W/cm2. We developed a three-level model to understand vapor dynamics near the interface and thermal conduction within the device, which showed good agreement with experiments. We then compared pore-level heat transfer of different fluids, where R245fa showed approximately 10 times the performance of water under the same working conditions. Finally, we illustrate the usefulness of a figure of merit extracted from the kinetic theory for evaporation. The current work provides fundamental insights into the evaporation of low surface tension liquids, which can impact various applications such as refrigeration and air conditioning, petroleum and solvent distillation, and on-chip electronics cooling.

New Model for Liquid Evaporation and Vapor Transport in Nanopores Covering the Entire Knudsen Regime and Arbitrary Pore Length

“…Laboratory experiments were also conducted using an anodic aluminum oxide (AAO) membrane evaporator. The experiments leveraged the advanced fabrication of an integrated heater and a resistance temperature detector, ,− overcoming the difficulty in measuring the liquid surface temperature. − The adoption of a thin membrane with nanopores ,, provides opportunities for studying liquid evaporation and vapor transport in nanoscale space. Through modeling, simulation, and experimental investigation, we aim at deriving a unified theory that captures the vapor transport resistance under the whole Knudsen regime, completing the modeling of evaporative heat transfer from nanopores …”

Evaporation from arbitrary nanoporous membrane configurations: An effective evaporation coefficient approach

“…To study thin-film-based nanoporous membrane cooling, there have been several reported studies analyzing evaporation in nanopores. 14,18,[22][23][24][25][26][27] In particular, Lu et al 24 recently demonstrated both experimentally and numerically that evaporation rates can be conveniently expressed as a function of the pressure ratio across the Knudsen layer, specifically for nanoporous configurations with relatively very low evaporation rates. However, this study was limited to low Mach number cases and did not explore the parametric effect of meniscus shape, Knudsen number, or porosity on the evaporation output parameters for different operating conditions.…”

Enhanced Evaporation of Ultrathin Water Films on Silicon-Terminated Si3N4 Nanopore Membranes

“…Evaporation on tiny pore structures is the most important driving force for the liquid transport process in plants. This mechanism has been adopted to develop new and critical techniques, such as membrane-based thermal desalination, − chip cooling, − solar-driven interfacial evaporation, , and nanofluidic generation. , For further improvement of these nanopore-evaporation-based devices, it is urgent to reveal the enhancement mechanism of nanothin liquid film evaporation on nanopore structures.…”