arXiv subjects

Michael T. Barako

Publications and source records attributed to Michael T. Barako.

4 recordsLinked to original sources

arXiv2026

Cavitation Dynamics in Venturi-Type Microchannels: Experimental Observations and Numerical Modeling

Cavitation in fluids can severely hinder the efficiency of the associated flows. This undesired phenomenon is strongly influenced by local flow conditions, flow orientation, proximity to boundaries and liquid/gas properties at saturation. When liquid flow is severely constricted and cavitation occurs, diverging microchannels can suppress vapor formation through effective pressure recovery; however, the behavior of such microchannels under different geometric and operating conditions remains unclear. This work combines experimental data and computational modeling to elucidate the intricate flow dynamics of cavitation-induced phase change of refrigerant (R134a) flow in a Venturi-type microchannel. Full-field numerical simulations are carried out using the interPhaseChangeFoam solver in OpenFOAM, with the model coefficients being validated against experimental data obtained with an identical system. The effects of flow rate, channel opening angle, and inlet cross-sectional geometry are explored with a focus on pressure drop, velocity distribution, and cavitation characteristics, including vapor fraction. The results highlight the roles of flow velocity, orifice-to-channel width ratio, orifice size, and channel divergence angle on overall pressure drop. A channel opening angle of 12 degrees minimizes pressure drop, in contrast with conventional single-phase Venturi geometries where the optimal opening angle typically lies between 5 and 7 degrees. The study underscores that the cavitation number, including its sign, serves as a critical quantitative indicator of cavitation severity where increasingly negative values correspond to intensified vapor generation in microscale constrictions. By identifying the relationships between operating conditions & cavitation phenomena, this work provides a framework for understanding and optimizing microchannel designs under conditions prone to cavitation.

physics.flu-dyn↗

arXiv2022

Deep Vision-Inspired Bubble Dynamics on Hybrid Nanowires with Dual Wettability

The boiling efficacy is intrinsically tethered to trade-offs between the desire for bubble nucleation and necessity of vapor removal. The solution to these competing demands requires the separation of bubble activity and liquid delivery, often achieved through surface engineering. In this study, we independently engineer bubble nucleation and departure mechanisms through the design of heterogeneous and segmented nanowires with dual wettability with the aim of pushing the limit of structure-enhanced boiling heat transfer performances. The demonstration of separating liquid and vapor pathways outperforms state-of-the-art hierarchical nanowires, in particular, at low heat flux regimes while maintaining equal performances at high heat fluxes. A machine vision-based framework realizes the autonomous curation and extraction of hidden big data along with bubble dynamics. The combined efforts of materials design, deep learning techniques, and data-driven approach shed light on the mechanistic relationship between vapor/liquid pathways, bubble statistics, and phase change performance.

physics.app-ph↗

arXiv2020

Approaching the Practical Conductivity Limits of Aerosol Jet Printed Silver

Previous efforts to directly write conductive metals have been narrowly focused on nanoparticle ink suspensions that require aggressive sintering (>200 °C) and result in low-density, small-grained agglomerates with electrical conductivities <25% of bulk metal. Here, we demonstrate aerosol jet printing of a reactive ink solution and characterize high-density (93%) printed silver traces having near-bulk conductivity and grain sizes greater than the electron mean free path, while only requiring a low-temperature (80 °C) treatment. We have developed a predictive electronic transport model which correlates the microstructure to the measured conductivity and identifies a strategy to approach the practical conductivity limit for printed metals. Our analysis of how grain boundaries and tortuosity contribute to electrical resistivity provides insight into the basic materials science that governs how an ink formulator or process developer might approach improving the conductivity. Transmission line measurements validate that electrical properties are preserved up to 20 GHz, which demonstrates the utility of this technique for printed RF components. This work reveals a new method of producing robust printed electronics that retain the advantages of rapid prototyping and three-dimensional fabrication while achieving the performance necessary for success within the aerospace and communications industries.

physics.app-ph↗

arXiv2020

Experimental Demonstration of Dynamic Thermal Regulation using Vanadium Dioxide Thin Films

We present an experimental demonstration of passive, dynamic thermal regulation in a solid-state system with temperature-dependent thermal emissivity switching. We achieve this effect using a multilayered device, comprised of a vanadium dioxide (VO2) thin film on a silicon substrate with a gold back reflector. We experimentally characterize the optical properties of the VO2 film and use the results to optimize device design. Using a calibrated, transient calorimetry experiment we directly measure the temperature fluctuations arising from a time-varying heat load. Under laboratory conditions, we find that the device regulates temperature better than a constant emissivity sample. We use the experimental results to validate our thermal model, which can be used to predict device performance under the conditions of outer space. In this limit, thermal fluctuations are halved with reference to a constant-emissivity sample.

physics.app-ph↗