Experimental Study of the Nano-Fin Effect (nFE) During Thin Film Evaporation From Nanopores in Anodic Aluminum Oxide (AAO) Membrane Substrates Integrated With Nano-Thermocouple / Thin Film Thermocouple (TFT) Array

Abstract

Recent advances in micro/nano-fabrication has enabled the deployment of nanostructured surfaces, nanochannels, and nanoporous membranes for development of new generation thermal management devices with remarkable potential for heat transfer enhancement. Anomalous heat transfer has been reported in studies involving heaters with nanostructured surfaces. For example, nanofins with lower thermal conductivity values can cause higher levels of enhancement in heat flux values, especially during phase change (such as for boiling on heaters with nanostructured surfaces). In addition, confinement of fluid in nanopores can also result in anomalous properties. This is manifest in anomalous production curves during hydraulic fracturing operations in oil and gas applications. A transport model that resolves these conundrums is termed as the “nanoFin Effect (nFE)”. nFE is governed by interfacial phenomena, i.e., the formation of thermal impedances in parallel circuit configuration, consisting of: (a) interfacial thermal resistance (also known as “Kapitza resistance”); (b) thermal capacitor; and (c) thermal diode (that form at the interface between each nanoparticle and the surface adsorbed thin-film of solvent molecules). nFE (i.e., primarily the interfacial thermal diode effect) also leads to preferential trapping of ions on the surface adsorbed thin film of solvent molecules leading to very high concentration gradients causing drastic reduction in corrosion. The motivation of this study was to explore nFE during thin film evaporation from nanopores. The methods used in this study include mounting a nano-thermocouple array (also termed as Thin Film Thermocouples or “TFT”) on a hot plate and observing the transient response recorded by the TFT array when a small liquid droplet (of fixed mass or volume) is dispensed on to an anisotropic AAO membrane containing nanopores. In this study, two different pore sizes were explored: 200 nm and 10 nm. The experiments were performed using isopropyl alcohol (IPA) droplets for four different temperature settings of the heated membrane (containing the nanopores).