Analytical, Numerical, and Experimental Investigation of Air- and Liquid-Based Synthetic Jet Devices for Next-Generation Solid-State Cooling in Data Centers and High-Flux Electronics

Abstract

Modern high-power electronic systems, specifically high-power computer chips, demand transformative liquid cooling solutions as traditional air cooling struggles to meet ever-increasing heat fluxes. In data centers, rising microprocessor thermal design powers—escalating from air cooling limits of 280 W to beyond 700 W—necessitate a shift toward liquid cooling. Thus, this dissertation begins with a literature survey on the necessity of liquid cooling in data centers. One key observation from this review establishes that while single-phase immersion cooling offers potential, it requires localized enhancement to overcome inherent inefficiencies. Rec- ognizing the promise of synthetic jet devices for targeted heat removal, this work pioneers the development of mesoscale Liquid Synthetic Jet Devices, a class previously explored mostly in air. To bridge this gap, dual air and water, analytical, numerical, and experimental studies were performed. Regarding air-based synthetic jet cooling, a new fabrication approach based on additive manufacturing was presented. This method enabled the production of ultra-thin devices— as thin as 4 mm—without mechanical fasteners and with complete freedom in device cavity design. Hotwire anemometry tests revealed air jet exit velocities exceeding 106 m/s using a single piezoelectric diaphragm, among the highest reported in the literature. Diaphragm deflection measurements were performed using a laser displacement sensor. Next, lumped element modeling, tuned solely on diaphragm deflection behavior, accurately predicted device performance and was validated using hotwire anemometry. By fabricating and testing multiple synthetic jet devices with different geometries, it was demonstrated that the impulse generation rate—which accounts for both jet velocity and flow rate—better correlates with enhanced heat transfer capabilities than jet velocity alone. Thermal tests showed that, compared to natural convection, the manufactured devices achieved over 13 times greater heat removal rates, with an average heat transfer coefficient exceeding 120 W/(m2·K) over a 30 mm × 30 mm heated surface.

Next, the fabrication extended to liquid synthetic jet device design and manufacturing. The devices were waterproofed and operated at higher voltages than air-based devices. Due to reduced operating frequencies, they achieved operational jet generation with minimal power consumption as low as 50 mW. In an immersion cooling test setup designed to evaluate liquid- based synthetic jet devices in deionized water, liquid synthetic jet impingement showed a heat transfer coefficient of up to 1.52 W/(cm2·K). Compared to existing methods, superior heat removal per unit of consumed power was achieved. This work demonstrates an advancement in sustainable thermal management, showing that such a small and inexpensive device can improve the coefficient of performance of single-phase immersion cooling by up to 12 times. Furthermore, the first lumped element model for liquid synthetic jet devices was proposed. Lastly, the analytical model was further studied in conjunction with numerical computa- tional fluid dynamics simulations and additional thermal tests in harsher environments. Fab- rication improvements increased the device’s operational frequency from 155 Hz to 210 Hz. Results demonstrated heat transfer enhancement, with the liquid synthetic jet device achieving a peak heat transfer coefficient of 1.7 W/(cm2·K), an 8.7-fold improvement over mixed convec- tion cooling, while maintaining low power consumption (0.22 W). The device cooled a 144 W heated surface from 72 °C to 31.5 °C under a crossflow rate of 2 GPM at 20 °C. Particle Image Velocimetry experiments and high-speed videography helped determine diaphragm deflection values based on a parametric study using computational fluid dynamics simulations. Later, lumped element models tuned with computational fluid dynamics results were used to under- stand liquid synthetic jet operation in an expanded frequency domain. This enabled the first report on the jet formation criterion for water-based liquid synthetic jet devices, with a value of +6 for circular orifices. Collectively, this dissertation charts a roadmap that unites immersion liquid cooling strate- gies with liquid synthetic jet technology, offering scalable, energy-efficient, and solid state and sustainable thermal management solution for next-generation data centers and high-power elec- tronics. Future work will explore multi-jet array configurations, enhanced surface integrations, optimized voltage amplification, and long-term reliability—particularly in two-phase immer- sion cooling environments—to further refine and commercialize this approach.