Liquid-vapor phase-change cooling has a significant potential to facilitate the development of highly dense electronics by leveraging latent heat during the phase transition to remove heat from hotspots. A promising form of liquid-vapor phase-change cooling is coalescence-induced jumping droplet condensation, where droplet growth results in coalescence and gravity-independent jumping from the cold surface due to capillary-inertial energy conversion. Once the departed droplets reach the hotspot, heat is extracted via evaporation and through vapor return, subsequently spreading to the cold surface via condensation. Realizing the full potential of jumping droplet cooling requires a detailed understanding of the physics governing the process. Here, we examine the fundamental thermal and hydrodynamic limits of jumping droplet condensation. We demonstrate that jumping is mainly governed by the rate of droplet growth and fluid thermophysical properties. Timescale analysis demonstrates that the upper bound of water vapor jumping droplet condensation critical heat flux is similar to 20kW/cm(2), significantly higher than that experimentally observed thus far due to surface structure limitations. Analysis of a wide range of available working fluids shows that liquid metals such as Li, Na, and Hg can obtain superior performance when compared to water.

This paper proposes a method for accurate temperature estimation of thermally-aware power electronics systems. The duality between electrical systems and thermal systems was considered for thermal modeling. High dimensional thermal models present a challenge for online estimation. Therefore, the complexity of the thermal network was reduced by applying a structure-preserving model order reduction technique. An optimal number and placement of temperature sensors were used in a Kalman filter to accurately estimate the dynamic spatial thermal behavior of the system. The optimal number of temperature sensors was found by comparing the actual values of the states obtained from the thermal model to the estimated values of the states obtained from the Kalman filter. The optimal placement of temperature sensors was found by maximizing the trace of the observability Gramian. Simulation and experimental results validate the approach on a prototype inverter.

Increasing electrification of mechanically controlled or driven systems has created a demand for the development of compact, lightweight electronics. Removing waste heat from these high volumetric and gravimetric power dense assemblies, especially in mobile applications, requires non-traditional thermal management strategies with high heat flux potential and low integration penalty. Here, we develop and study confined subcooled pool boiling on nanoengineered surfaces which enables self-assembly of liquid bridges capable of high heat flux dissipation without external pumping. Using high-speed optical imaging coupled with high-fidelity heat transfer experiments in pure vapor environments, we study the physics of liquid bridge formation, bridge lifetime, and heat transfer. We demonstrate heat flux dissipations >100 W/cm(2) from a gallium nitride (GaN) power transistor residing above a horizontally parallel superhydrophobic nanostructured aluminum cold plate. To understand the confined bridge dynamics, we develop a hydrodynamic droplet bridging model and design rules capable of predicting the effects of gravity, intrinsic contact angle, contact angle hysteresis, and device heat flux. Our work not only demonstrates an ultra-efficient mechanism of heat dissipation and spreading using nanoengineered surfaces coupled to fluid confinement, but also enables the development of fully three-dimensional integrated electronics. (C) 2018 Elsevier Ltd. All rights reserved.

Multilevel topologies are an appealing method to achieve higher power density converters for both mobile and stationary systems. This article discusses the design and high-performance hardware implementation of a 13-level, flying capacitor multilevel (FCML) inverter. Derivation of flying capacitor sizing for ac output voltages (for an arbitrary level FCML) is provided. Operating from an 800-Vdc bus, this hardware prototype utilizes switch modules with 100-V rating. Moreover, a 120-kHz switching frequency is enabled through the use of gallium nitride (GaN) FETs and the development of custom-integrated switching cells, which reduce commutation loop inductance and allow for a modular design. The frequency multiplication effect of FCML inverters allows the output inductor of the inverter to be made exceptionally small (4.7 mu H) while maintaining a 0.7% total harmonic distortion (THD) due to the 1.44-MHz effective inductor ripple frequency.

This article reports the design, fabrication, and demonstration of additively manufactured air jet impingement coolers for the thermal management of high-power gallium nitride (GaN) transistors. The polymer jet coolers impinge high-speed airflow with a velocity of 42 & x2013;195 m/s (Reynolds number between onto working GaN devices mounted on a printed circuit board (PCB). The air jet provides cooling heat fluxes of up to 58.4 W/cm(2), cooling rates of up to 6.6 & x00B0;C/s, and convective heat transfer coefficient ranging from 5.2 to 17.0 kW/). The cooling performance is comparable to that of jet coolers made from other materials and manufacturing technologies. A key benefit of additive manufacturing (AM) is design freedom and geometric complexity, which we highlight by demonstrating three different packaging configurations, each enabled by a different jet cooler design that is customized for different types of packaging configurations: Cooler 1 directs two parallel impinging jets onto the top side of two devices; cooler 2 directs two air jets onto the front side and two air jets onto the back side of two devices; and cooler 3 directs air jets onto the front side of four devices mounted on parallel adjacent circuit boards. The second benefit of AM is the ability to consolidate multiple components into a single part, which we highlight by combining a nozzle, a fluidic delivery system, and a flow distributor within a volume of 80 mm mm. This work demonstrates the potential of AM to create complex, lightweight, fluidic delivery systems to achieve thermally and hydrodynamically optimized air jet cooling for high-power-density electronic devices.

Single-phase inverters and rectifiers require the use of an energy buffer to absorb twice-line-frequency power ripple. Historically, this challenge has been addressed by the use of large electrolytic capacitors. Lifetime constraints and the need for improved system performance have motivated designers to seek other capacitor technologies, such as ceramic and film, which are frequently used in conjunction with active filtering converters to reduce the capacitance required. Active filtering converters cycle the capacitor voltage over a wide voltage range while maintaining a constant dc bus voltage. This large-swing operation demands different capacitor qualities than most other filtering applications, and the data sheet parameters available for commercial capacitors may be ineffective or require special care for calculating characteristics, such as efficiency and energy storage capability. This work presents an experimental setup for evaluating capacitor performance under a large voltage swing along with detailed experimental results. Energy storage data for a number of capacitors in the 50-630 V range from several manufacturers are included. The approach and findings of this paper can serve as an aid to power electronics designers for the selection and evaluation of capacitors in energy buffering applications.

The S100 family protein p11 (S100A10, annexin 2 light chain) is involved in the trafficking of the voltage-gated sodium channel Na(V)1.8, TWIK-related acid-sensitive K+ channel (TASK-1), the ligand-gated ion channels acid-sensing ion channel 1a (ASIC1a) and transient receptor potential vanilloid 5/6 (TRPV5/V6), as well as 5-hydroxytryptamine receptor 1B (5-HT1B), a G-protein-coupled receptor. To evaluate the role of p11 in peripheral pain pathways, we generated a loxP-flanked (floxed) p11 mouse and used the Cre-loxP recombinase system to delete p11 exclusively from nociceptive primary sensory neurons in mice. p11-null neurons showed deficits in the expression of NaV1.8, but not of annexin 2. Damage-sensing primary neurons from these animals show a reduced tetrodotoxin-resistant sodium current density, consistent with a loss of membrane-associated NaV1.8. Noxious coding in wide-dynamic-range neurons in the dorsal horn was markedly compromised. Acute pain behavior was attenuated in certain models, but no deficits in inflammatory pain were observed. A significant deficit in neuropathic pain behavior was also apparent in the conditional-null mice. These results confirm an important role for p11 in nociceptor function.

Vapor condensation is a widely used industrial process for transferring heat and separating fluids. Despite progress in developing low surface energy hydrophobic and micro/nanostructured superhydrophobic coatings to enhance water vapor condensation, demonstration of stable dropwise condensation of low-surface-tension fluids has not been achieved. Here, we develop rationally designed nanoengineered lubricant-infused surfaces (LISs) having ultralow contact angle hysteresis (<3 degrees) for stable dropwise condensation of ethanol (gamma approximate to 23 mN/m) and hexane (gamma approximate to 19 mN/m). Using a combination of optical imaging and rigorous heat transfer measurements in a controlled environmental chamber free from noncondensable gases (<4 Pa), we characterize the condensation behavior of ethanol and hexane on ultrascalable nanostructured CuO surfaces impregnated with fluorinated lubricants having varying viscosities (0.496 < mu < 5.216 Pa.s) and chemical structures (branched versus linear, Krytox and Fomblin). We demonstrate stable dropwise condensation of ethanol and hexane on LISs impregnated with Krytox 1525, attaining about 200% enhancement in condensation heat transfer coefficient for both fluids compared to filmwise condensation on hydrophobic surfaces. In contrast to previous studies, we use 7 h of steady dropwise condensation experiments to demonstrate the importance of rational lubricant selection to minimize lubricant drainage and maximize LIS durability. This work not only demonstrates an avenue to achieving stable dropwise condensation of ethanol and hexane, it develops the fundamental design principles for creating durable LISs for enhanced condensation heat transfer of low-surface tension fluids.