Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 100239

100239 - 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 

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).

The experimental apparatus includes a silicon wafer with surface-micro-machined nano-thermocouples (using photolithography, followed by two sets of metal deposition in conjunction with the “lift-off” process). Hence, the nano-thermocouples were micro-fabricated on a silicon wafer substrate and consisted metal strips obtained by thin-film deposition (thus constituting the thermocouples at the junctions of these two sets of deposited metals/ alloys). These thin-film metal strips are made from Alumel (with negative polarity) and Chromel (with positive polarity). The TFT array consists of 6 different thermocouples (6 pairs of metals deposited to form each junction), as shown in the diagram below. The thermocouple leveraged for this experiment is labeled as “TC 1” in the diagram (Fig. 1). This nano-thermocouple (TFT) was placed in the center of a hot plate. The hot plate setting was fixed at four different temperature values until steady state temperature conditions were obtained throughout the experiment. The steady-state temperature settings of the hot plate used for these experiments were 30°C, 40°C, 50°C, and 60°C. After setting the hot plate to a designated temperature value, it was allowed to stabilize for 30 minutes (in order to achieve steady state temperature conditions) before proceeding with initiating each experiment.

The AAO membrane used in each experiment is placed at the center of the silicon wafer with the array of nano-thermocouples (i.e., the array of 6 TFT junctions) centered below the membrane and touching the bottom surface of the AAO membrane. The AAO membrane is mounted carefully and positioned on the silicon wafer (containing the TFT array on its top surface) using a pair of calipers for ensuring that they are contacting the leads for the thermocouple . These are anisotropic ceramic membranes containing arrays of nanopores that are formed from a self-organized etching of cavities in aluminum oxide.  Two different types of membranes were used in these experiments, with one set of AAO membranes containing nanopores with a diameter of 200 nm, and the other AAO membrane containing nanopores of 10 nm diameter.

Presenting Author: Julie Shafer TAMU

Presenting Author Biography: Ms. Shafer is a graduate student at TAMU

Authors:

Julie Shafer TAMU
Jonghyun Lee TAMU
Ashok Thyagarajan TAMU
Debjyoti Banerjee Texas A&M University