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The advancement of liquid phase electron/ion beam induced deposition has enabled an effective direct-write approach for functional nanostructure synthesis with the possibility of three-dimensional control of morphology. For formation of a metallic solid phase, the process employs ambient temperature, beam-guided, electrochemical reduction of precursor cations, resulting in rapid formation of structures, but with challenges for retention of resolution achievable via slower electron beam approaches. The possibility of spatial control of redox pathways via the use of water–ammonia solvents has opened avenues for improved nanostructure resolution without sacrificing the growth rate. In particular, ammonia enables "electrochemical lensing" in which a tightly confined and highly reducing environment is created locally to enable high resolution, rapid beam-directed nanostructure growth. We demonstrate this unique approach to high resolution synthesis through a combination of analysis and experiment. [ABSTRACT FROM AUTHOR]

In recent years, cell-based therapies have transformed medical treatment. These therapies present a multitude of challenges associated with identifying the mechanism of action, developing accurate safety and potency assays, and achieving low-cost product manufacturing at scale. The complexity of the problem can be attributed to the intricate composition of the therapeutic products: living cells with complex biochemical compositions. Identifying and measuring critical quality attributes (CQAs) that impact therapy success is crucial for both the therapy development and its manufacturing. Unfortunately, current analytical methods and tools for identifying and measuring CQAs are limited in both scope and speed. This Perspective explores the potential for microfluidic-enabled mass spectrometry (MS) systems to comprehensively characterize CQAs for cell-based therapies, focusing on secretome, intracellular metabolome, and surfaceome biomarkers. Powerful microfluidic sampling and processing platforms have been recently presented for the secretome and intracellular metabolome, which could be implemented with MS for fast, locally sampled screening of the cell culture. However, surfaceome analysis remains limited by the lack of rapid isolation and enrichment methods. Developing innovative microfluidic approaches for surface marker analysis and integrating them with secretome and metabolome measurements using a common analytical platform hold the promise of enhancing our understanding of CQAs across all "omes," potentially revolutionizing cell-based therapy development and manufacturing for improved efficacy and patient accessibility. [ABSTRACT FROM AUTHOR]

Brain temperature, regulated by the balance between blood circulation and metabolic heat generation, is an important parameter related to neural activity, cerebral hemodynamics, and neuroinflammation. A key challenge for integrating brain temperature into clinical practice is the lack of reliable and non-invasive brain thermometry. The recognized importance of brain temperature and thermoregulation in both health and disease, combined with limited availability of experimental methods, has motivated the development of computational thermal models using bioheat equations to predict brain temperature. In this mini-review, we describe progress and the current state-of-the-art in brain thermal modeling in humans and discuss potential avenues for clinical applications. [ABSTRACT FROM AUTHOR]

Brain temperature is an understudied parameter relevant to brain injury and ischemia. To advance our understanding of thermal dynamics in the human brain, combined with the challenges of routine experimental measurements, a biophysical modeling framework was developed to facilitate individualized brain temperature predictions. Model-predicted brain temperatures using our fully conserved model were compared with whole brain chemical shift thermometry acquired in 30 healthy human subjects (15 male and 15 female, age range 18–36 years old). Magnetic resonance (MR) thermometry, as well as structural imaging, angiography, and venography, were acquired prospectively on a Siemens Prisma whole body 3 T MR scanner. Bland–Altman plots demonstrate agreement between model-predicted and MR-measured brain temperatures at the voxel-level. Regional variations were similar between predicted and measured temperatures (< 0.55 °C for all 10 cortical and 12 subcortical regions of interest), and subcortical white matter temperatures were higher than cortical regions. We anticipate the advancement of brain temperature as a marker of health and injury will be facilitated by a well-validated computational model which can enable predictions when experiments are not feasible. [ABSTRACT FROM AUTHOR]

The exceptional photochromic and redox properties of polyoxometalate anions, PW12O403−, have been exploited to develop an integrated photoelectrochemical energy storage cell for conversion and storage of solar energy. Elimination of strongly coordinating cations using benchtop ion soft landing leads to a ∼370% increase in the maximum power output of the device. Additionally, the photocathode displayed a pronounced color change from clear to blue upon irradiation, which warrants the potential application of the IPES cell in advanced smart windows and photochromic lenses. [ABSTRACT FROM AUTHOR]

Real-time, advanced diagnostics of the biochemical state within cells remains a significant challenge for research and development, production, and application of cell-based therapies. The fundamental biochemical processes and mechanisms of action of such advanced therapies are still largely unknown, including the critical quality attributes that correlate to therapeutic function, performance, and potency and the critical process parameters that impact quality throughout cell therapy manufacturing. An integrated microfluidic platform has been developed for in-line analysis of a small number of cells via direct infusion nano-electrospray ionization mass spectrometry. Central to this platform is a microfabricated cell processing device that prepares cells from limited sample volumes removed directly from cell culture systems. The sample-to-analysis workflow overcomes the labor intensive, time-consuming, and destructive nature of existing mass spectrometry approaches for analysis of cells. By providing rapid, high-throughput analyses of the intracellular state, this platform enables untargeted discovery of critical quality attributes and their real-time, in-process monitoring. [ABSTRACT FROM AUTHOR]

Brain temperature is an important yet understudied medical parameter, and increased brain temperature after injury is associated with worse patient outcomes. The scarcity of methods for measuring brain temperature non-invasively motivates the need for computational models enabling predictions when clinical measurements are challenging. Here, we develop a biophysical model based on the first principles of energy and mass conservation that uses data from magnetic resonance imaging of individual brain tissue and vessel structure to facilitate personalized brain temperature predictions. We compare model-predicted 3D thermal distributions with experimental temperature measured using whole brain magnetic resonance-based thermometry. We find brain thermometry maps predicted by the model capture unique spatial variations for each subject, which are in agreement with experimentally-measured temperatures. As medicine becomes more personalized, this foundational study provides a framework to develop an individualized approach for brain temperature predictions. While progress has been made to formulate models for brain temperature regulation that incorporate non-simplified anatomy and vasculature, accounting for heterogeneity between individuals is still a challenge. Here, the authors propose a fully conserved biophysical model that, starting from an individual subject's magnetic resonance-derived tissue and vessel structure, predicts individual patterns in local brain temperature in agreement with magnetic resonance thermometry. [ABSTRACT FROM AUTHOR]

Vortical jet flows in the Reynolds number (Re) range from 1000 to 3425 and swirl number (S) below 0.5, alone and in combination with suction through a small aperture, are experimentally investigated using optical visualization. Schlieren photography is employed to assess the vortical flow structure and establish the fundamental understanding of the source-to-sink gas-dynamic coupling, including the role played by the flow rate, jet diameter, and separation distance between the gas jet source and the suction sink. Compared to vortex-free jets, vortical jets for Re > 2700 with swirl number S > 0.27 experience earlier laminar-to-turbulent transition, resulting in a rapid growth of the jet boundary. The ability to control the growth of the jet expansion and mass and momentum dissipation into the surrounding is demonstrated via the use of a coaxially aligned flow suction placed in the path of a jet. When a swirling jet is completely coupled with a flow suction, jet expansion is significantly suppressed. The suction/sink flow rate imposes a limit on the maximum input/source flow rate of the gas jet to achieve complete coupling. Furthermore, there is a maximum distance over which effective coupling can occur, and for all Reynolds numbers considered, this distance is shorter than the distance at which the jet structure breaks up into turbulent eddies in the absence of a sink. [ABSTRACT FROM AUTHOR]

A sodium thermal electrochemical converter (Na‐TEC) generates electricity directly from heat through isothermal expansion of sodium ions across a beta″‐alumina solid‐electrolyte. This heat engine has been considered for use with conventional concentrating solar power (CSP) systems before. However, unlike previous single‐stage devices, the improved design uses two stages with an interstage reheat, allowing more economical and efficient conversion up to 29% at a hot side temperature of 850 °C. Herein, a cost‐performance analysis for this improved design assesses opportunities for distributed‐CSP in the context of micro‐combined heat and power systems. A high‐level techno‐economic analysis (TEA) is presented that explores four scenarios where a Na‐TEC is used as the heat engine for a distributed‐CSP system. Overnight capital cost and levelized cost of electricity (LCOE) are estimated for a system lifetime of 30 years, revealing that overnight capital costs in a range from $3.57 to $17.71 per We are feasible, which equate to LCOEs from 6.9 to 17.2 cents kWhe−1. This analysis makes a significant contribution by concurrently quantifying the efficiency and unit costs for a range of multistage configurations, and demonstrating that a Na‐TEC may be a promising alternative to Stirling engines for distributed‐CSP systems at residential scale of 1–5 kWe. [ABSTRACT FROM AUTHOR]

In this work we have developed a comprehensive dynamic model of electron beam induced deposition (EBID) of residual hydrocarbon coupling mass transport, electron transport and scattering, and species decomposition to predict the deposition of carbon nanopillars. The simulations predict the local species and electron density distributions, as well as the three-demensional morphology and the growth rate of the deposit. Since the process occurs in a high vacuum environment, surface diffusion is considered as the primary transport mode of surface-adsorbed hydrocarbon precursor. The governing surface transport equation (STE) of the adsorbed species is derived and solved numerically. The transport, scattering, and absorption of primary electron as well as secondary electron generation are treated using the Monte Carlo method. Low energy secondary electrons are the major contributors to hydrocarbon decomposition due to their energy range matching peak dissociation reaction cross section energies for precursor molecules. The deposit and substrate are treated as a continuous entity allowing the simulation of the growth of a realistically sized deposit rather than a large number of cells representing each individual atom as in previously published simulations [Mitsuishi et al., Ultramicroscopy 103, 17 (2005); Silvis-Cividjian, Ph.D. thesis, University of Delft, 2002]. Such formulation allows for simple coupling of the STE with the dynamic growth of the nanopillar. Three different growth regimes occurring in EBID are identified using scaling analysis, and simulations are used to describe the deposit morphology and precursor surface concentration specific for each growth regime. [ABSTRACT FROM AUTHOR]

A new state of radical thermal non-equilibrium in surface adsorbed molecules is discovered that enables rapid surface diffusion of energized adatoms with a negligible effect on the substrate surface temperature. Due to enhanced surface diffusion, growth rates can be achieved that improve the feasibility of many nanofabrication techniques. Since the adatom temperature cannot be directly measured without disturbing its thermodynamic state, the first principle hard-cube model is used to predict both the adatom effective temperature and the surface temperature in response to gaseous particle impingement in a vacuum. The validity of the approach is supported by local, spatially-resolved surface temperature measurements of the thermal response to supersonic microjet gas impingement. The ability to determine and control the adatom effective temperature, and therefore the surface diffusion rate, opens new degrees of freedom in controlling a wide range of nanofabrication processes that critically depend on surface diffusion of precursor molecules. This fundamental understanding has the potential to accelerate research into nanoscale fabrication and to yield the new materials with unique properties that are only accessible with nanoscale features. [ABSTRACT FROM AUTHOR]

Large‐scale manufacturing of therapeutic cells requires bioreactor technologies with online feedback control enabled by monitoring of secreted biomolecular critical quality attributes (CQAs). Electrospray ionization mass spectrometry (ESI‐MS) is a highly sensitive label‐free method to detect and identify biomolecules, but requires extensive sample preparation before analysis, making online application of ESI‐MS challenging. We present a microfabricated, monolithically integrated device capable of continuous sample collection, treatment, and direct infusion for ESI‐MS detection of biomolecules in high‐salt solutions. The dynamic mass spectrometry probe (DMSP) uses a microfluidic mass exchanger to rapidly condition samples for online MS analysis by removing interfering salts, while concurrently introducing MS signal enhancers to the sample for sensitive biomolecular detection. Exploiting this active conditioning capability increases MS signal intensity and signal‐to‐noise ratio. As a result, sensitivity for low‐concentration biomolecules is significantly improved, and multiple proteins can be detected from chemically complex samples. Thus, the DMSP has significant potential to serve as an enabling portion of a novel analytical tool for discovery and monitoring of CQAs relevant to therapeutic cell manufacturing. Large‐scale manufacturing of therapeutic cells requires bioreactor technologies with online feedback control enabled by monitoring of secreted biomolecular critical quality attributes (CQAs). Electrospray ionization mass spectrometry (ESI‐MS) is a highly sensitive label‐free method to detect and identify biomolecules, but requires extensive sample preparation before analysis, making online application of ESI‐MS challenging [ABSTRACT FROM AUTHOR]

As microelectronic system density continues to increase, cooling with conventional technologies continues to become more challenging and is often a limiter of performance and efficiency. The challenge arises due to both large heat fluxes generated across entire chips and packages, and localized hotspots with even higher heat flux. In this paper, nonuniform micropin-fin heat sinks are investigated for the cooling of integrated circuits with nonuniform power maps. Four heterogeneous micropin-fin samples were fabricated and tested in single-phase experiments with deionized water to investigate the effectiveness of local micropin-fin clustering for the cooling of hotspots. Cylindrical and hydrofoil micropin-fins were tested, as well as two types of heterogeneous arrays: those with pin-fins clustered directly over the hotspot and those with the high density cluster spanning the entire width of the channel to prevent flow bypass around the cluster. Samples were tested with a uniform nominal heat flux of 250 W/cm2 as well as a hotspot heat flux of 500 W/cm2. Local micropin-fin clustering was found to be an effective method of reducing local thermal resistance with a modest pressure drop penalty. [ABSTRACT FROM PUBLISHER]

We report on an improved Focused Electron Beam Induced Etching (FEBIE) process, which exploits heated oxygen delivery via a continuous supersonic micro-jet resulting in faster graphene patterning and better etch feature definition. Positioning a micro-jet in close proximity to a graphene surface with minimal jet spreading due to a continuous regime of gas flow at the exit of the 10 μm inner diameter capillary allows for focused exposure of the surface to reactive oxygen at high mass flux and impingement energy of a supersonic gas stream localized to a small etching area exposed to electron beam. These unique benefits of focused supersonic oxygen delivery to the surface enable a dramatic increase in the etch rate of graphene with no parasitic carbon "halo" deposition due to secondary electrons from backscattered electrons (BSE) in the area surrounding the etched regions. Increase of jet temperature via local nozzle heating provides means for enhancing kinetic energy of impinging oxygen molecules, which further speed up the etch, thus minimizing the beam exposure time and required electron dose, before parasitic carbon film deposition due to BSE mediated decomposition of adsorbed hydrocarbon contaminants has a measurable impact on quality of graphene etched features. Interplay of different physical mechanisms underlying an oxygen micro-jet assisted FEBIE process is discussed with support from experimental observations. [ABSTRACT FROM AUTHOR]

Purpose – The aim of this paper is to advance the understanding of the droplet deposition process to better predict and control the manufacturing results for ink-jet deposition. Design/methodology/approach – As material interface has both geometric and physical significance to manufacturing, the approach the authors take is to study the interface evolution during the material joining process in ink-jet deposition using a novel shape metric and a previously developed powerful simulation tool. This tool is an experimentally validated numerical solver based on the combination of the lattice Boltzmann method and the phase-field model that enabled efficient simulation of multiple-droplet interactions in three dimensions. Findings – The underlying physics of two-droplet interaction is carefully examined, which provides deep insights into the effects of the printing conditions on the interface evolution of multiple-droplet interaction. By studying line printing, it is found that increasing impact velocity or decreasing fluid viscosity can reduce manufacturing time. For array printing, the authors have found the issue of air bubble entrapment that can lead to voids in the manufactured parts. Research limitations/implications – The array of droplets impinges simultaneously, in contrast to most ink-jet printers. Sequential impingement of lines of droplet needs to be studied. Also, impingement on non-planar surfaces has not been investigated yet, but is important for additive manufacturing. Finally, it is recognized that the droplet hardening mechanisms need to be incorporated in the simulation tool to predict and control the final shape and size of the arbitrary features and manufacturing time for ink-jet deposition. Practical implications – The research findings in this paper imply opportunities for optimization of printing conditions and print head design. Furthermore, if precise droplet control can be achieved, it may be possible to eliminate the need for leveling roller in the current commercial printers to save machine and manufacturing cost. Originality/value – This work represents one of the first attempts for a systematic study of the interface dynamics of multiple-droplet interaction in ink-jet deposition enabled by the novel shape metric proposed in the paper and a previously developed numerical solver. The findings in this paper advanced the understanding of the droplet deposition process. The physics-based approach of analyzing the simulation results of the interface dynamics provides deep insights into how to predict and control the manufacturing relevant outcomes, and optimization of the deposition parameters is made possible under the same framework. [ABSTRACT FROM AUTHOR]

We report on a method for "direct-write" conductive patterning via reduction of graphene oxide (GO) sheets using focused electron beam induced deposition (FEBID) of carbon. FEBID treatment of the intrinsically dielectric graphene oxide between two metal terminals opens up the conduction channel, thus enabling a unique capability for nanoscale conductive domain patterning in GO. An increase in FEBID electron dose results in a significant increase of the domain electrical conductivity with improving linearity of drain-source current vs. voltage dependence, indicative of a change of graphene oxide electronic properties from insulating to semiconducting. Density functional theory calculations suggest a possible mechanism underlying this experimentally observed phenomenon, as localized reduction of graphene oxide layers via interactions with highly reactive intermediates of electron-beam-assisted dissociation of surface-adsorbed hydrocarbon molecules. These findings establish an unusual route for using FEBID as nanoscale lithography and patterning technique for engineering carbon-based nanomaterials and devices with locally tailored electronic properties. [ABSTRACT FROM AUTHOR]

A hybrid cooling scheme utilizing superlattice coolers (SLCs) along with microchannel heat sink for thermal management of hotspots is presented. In this paper, we have studied the effect of operating and design parameters on the performance of the SLC. We have also experimentally investigated the effect of interface thermal resistance as well as thermal resistance between the ground electrode and superlattice using two test configurations: one with on-chip microchannels and another with off-chip microchannels. We demonstrated heat removal capability at the localized hotspots of more than over 300 W/cm2. [ABSTRACT FROM AUTHOR]

Thermal coupling between superlattice coolers (SLCs) in an array adversely affects performance of an each individual cooler compared with an isolated device. Here, we have developed an electrothermal model to study this coupling between SLCs and how it is affected by geometric parameters such as separation between the superlattice structure and a ground electrode, and operating parameters such as the convective heat transfer coefficient and the activation current applied for driving the SLC. Complementary to the modeling efforts, we have also experimentally studied thermal coupling between SLCs in a microfabricated array under various conditions. Simulation results are critically compared against the experimental data and yield the conclusions of importance for an optimized design of the hybrid microfluidic SLC cooling scheme for thermal management of multiple clustered hotspots in microprocessors. We have observed more than 60% reduction in cooler performance, when placed within the few characteristic diameters of the ground electrode, due to thermal coupling effect. Thermal properties of the working fluid have even more pronounced effect on the thermal coupling between the coolers. [ABSTRACT FROM PUBLISHER]

A shape coefficient is introduced to quantify droplet shape by measuring its similarity to a desired shape to enable the study of droplet shape evolution upon impingement on a solid surface. Parametric simulations are performed with an experimentally validated numerical model to determine the impact conditions to maximize the shape coefficient. Results show that the Weber number is the controlling factor that determines the maximum achievable shape coefficient and the time instant when it is achieved for small Ohnesorge numbers, whereas the Reynolds number becomes the key parameter defining the optimal shape when the Ohnesorge number is large. A regime map is also developed to define the regions where a desired droplet shape can be achieved without splash. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3071-3082, 2013 [ABSTRACT FROM AUTHOR]

Reduction in contact resistance is one of the foremost challenges for carbon nanotube/graphene nanodevices. In this study, we present a novel fabrication process for low-temperature, Ohmic contact between open-ended multiwalled carbon nanotubes (MWCNTs) and metal interconnects using graphitic carbon deposited via electron beam-induced deposition (EBID). The electrical and structural properties of the contact interface are characterized for making connection to the single (outermost) shell only, as well as to multiple conducting shells of MWCNTs. In addition to establishing the scaling relationship between the carbon contact length and the resulting contact resistance, the magnitude of the contact resistance has been quantified with and without post-deposition thermal annealing. The results indicate that the contact is Ohmic in nature, and ranges from 26.5 kΩ for the connection made to the outermost shell of an MWCNT down to just 116 Ω for the multiple-shell connection performed via a process suggested through the EBID process simulations. These results provide a significant advance in application of MWCNTs to future interconnect technologies. [ABSTRACT FROM PUBLISHER]

We have developed a reduced-order, physics-based model of gas cloud transport and combined it with an approximate formulation of the equation of radiative transport to enable efficient prediction of spectral irradiation for simulation of hyperspectral infrared sensors. The resulting combined model is easily implemented, providing a rapid and flexible in silico experimentation capability. The gas cloud model is based on the entrainment hypothesis and predicts cloud trajectories in threedimensions, with elevation changes occurring primarily due to buoyancy effects and with spreading and accompanying dilution and cooling occurring due to a turbulence dominated growth mechanism. The radiation transport model is simplified through an approximate treatment of scattering that transforms the governing equation from an integro-differential equation to an ordinary differential equation. The conjugate model has been combined with a simple sensor model and has been validated through comparison to results from large-scale field tests. The utility of the simulations has also been demonstrated through inclusion in a larger algorithm development and analysis program, the chem/bio algorithm development kit. [ABSTRACT FROM AUTHOR]

Ink-jet deposition enables more efficient, economic, scalable manufacturing for a wide variety of materials than other additive techniques. The impact of droplets onto a substrate is critical for accuracy control and optimisation of the droplet deposition process. However, most previous research about droplet impact focused on the spreading radius of the droplet, which does not provide enough information for manufacturing purposes. This paper presents a new measure of droplet shape characterisation so that the droplet deposition process can be optimised to build desired geometries. A dimensional analysis is conducted to reduce the number of parameters of the impact conditions. Then the shape evolution of a wide range of impact conditions is simulated with a validated numerical model. The effects of the dimensionless numbers on the shape evolution are examined and analysed. Successive multiple droplets impact is also investigated. [ABSTRACT FROM PUBLISHER]

Distinct regimes of droplet charging, determined by the dominant charge transport process, are identified for an ultrasonic droplet ejector using electrohydrodynamic computational simulations, a fundamental scale analysis, and experimental measurements. The regimes of droplet charging are determined by the relative magnitudes of the dimensionless Strouhal and electric Reynolds numbers, which are a function of the process (pressure forcing), advection, and charge relaxation time scales for charge transport. Optimal (net maximum) droplet charging has been identified to exist for conditions in which the electric Reynolds number is of the order of the inverse Strouhal number, i.e., the charge relaxation time is on the order of the pressure forcing (droplet formation) time scale. The conditions necessary for optimal droplet charging have been identified as a function of the dimensionless Debye number (i.e., liquid conductivity), external electric field (magnitude and duration), and atomization drive signal (frequency and amplitude). The specific regime of droplet charging also determines the functional relationship between droplet charge and charging electric field strength. The commonly expected linear relationship between droplet charge and external electric field strength is only found when either the inverse of the Strouhal number is less than the electric Reynolds number, i.e., the charge relaxation is slower than both the advection and external pressure forcing, or in the electrostatic limit, i.e., when charge relaxation is much faster than all other processes. The analysis provides a basic understanding of the dominant physics of droplet charging with implications to many important applications, such as electrospray mass spectrometry, ink jet printing, and drop-on-demand manufacturing. [ABSTRACT FROM AUTHOR]

Using the governing equations for internal fluid flow and heat transfer, scaling laws are developed to predict how the selection of a liquid or gas coolant and geometry affects the pumping power and volume requirements of heat sinks in electronics cooling applications. One of the principal outcomes of the presented scaling analysis is derivation, based on first principles, of new figure-of-merit parameters that can be used to evaluate cooling performance and guide efforts on development of new cooling fluids. The new figures-of-merits are critically compared to existing performance metrics and experimental data from the literature to emphasize the relevance and accuracy of developed scaling laws. [ABSTRACT FROM AUTHOR]

To address the thermal management challenges associated with high power dissipation devices, we describe a novel hybrid thermal management device that enables significant enhancement of conventional air-cooled heat sinks using on-demand and spatially controlled droplet/jet impingement evaporative cooling. The device architecture modifies an air (gas)-cooled heat sink by adding a multiplexed, planar microelectromechanical system (MEMS)-based droplet ejector array as a capping surface of the finned structure of a conventional heat sink. Such a minimal modification of the heat sink allows one to exploit high heat flux evaporative cooling by virtue of delivering streams of liquid droplets or jets to the highly thermally conducting heat-spreading surface of the heat sink fins. The phase change associated with liquid droplet evaporation results in significant (∼50%) enhancement of the dissipated thermal load, beyond what could be achieved by using air (gas) cooling alone. Finally, among the additional key attractive features of the described technology is its ease of implementation (i.e., modification of commercially available heat sinks), paving the way to power-efficient, low-cost thermal management of high power dissipation devices. [ABSTRACT FROM AUTHOR]

In this article we describe a novel cooling scheme utilizing a combination of fluidic (single-phase convection and phase change) and solid-state (superlattice cooler) techniques to simultaneously remove high background heat fluxes (∼100 W/cm2) over the entire chip and dissipate ultra high heat fluxes (∼0.5-1 kW/cm2) from multiple localized hot spots. This article focuses on the conceptual design to assess the feasibility of the proposed cooling scheme. [ABSTRACT FROM AUTHOR]

A new cooling scheme utilizing evaporation from an ultrathin, spatially confined liquid film is described and analyzed for thermal management of hot spots with local heat fluxes in excess of 600 W/cm2. This is achieved by a stable monolayer of liquid maintained on the surface and using fully dry sweeping gas (e.g., air) blown at high velocity (50-100 m/s) above this liquid monolayer. We also demonstrate how dielectric coolants like FC72 can outperform water as an evaporative coolant for this scheme. This work presents the conceptual system design, the results of performance analysis supporting the feasibility of the proposed cooling scheme, and experimental results that demonstrate the idea as well as validate the computational results. The analysis allows one to elucidate the salient physical features of evaporative cooling from spatially confined thin films subjected to a sweeping gas and to identify the key parameters resulting enhanced performance. The simplified model provides results in a form suitable for designing a full-scale cooling device (perspiration nanopatch) that exploits the unique advantages of the proposed cooling scheme. [ABSTRACT FROM AUTHOR]

A dual-sample ultrasonic droplet ejector array is developed for use as a soft-ionization ion source for multiplexed mass spectrometry (MS). Such a multiplexed ion source aims to reduce MS analysis time for multiple analyte streams, as well as allow for the synchronized ejection of the sample(s) and an internal standard for quantitative results and mass calibration. Multiplexing is achieved at the device level by division of the fluid reservoir and separating the active electrodes of the piezoelectric transducer for isolated application of ultrasonic wave energy to each domain. The transducer is mechanically shaped to further reduce the acoustical crosstalk between the domains. Device design is performed using finite-element analysis simulations and supported by experimental characterization. Isolated ejection of ∼5 μm diameter water droplets from individual domains in the micromachined droplet ejector array at around 1 MHz frequency is demonstrated by experiments. The proof-of-concept demonstration using a dual-sample device also shows potential for multiplexing with larger numbers of analytes. [ABSTRACT FROM AUTHOR]

The second part in this series presents parametric simulation and sensitivity analysis of methane partial oxidation in a microreactor operated with periodic flow reversal. The reverse-flow (RF) operation provides up to a 5% increase in the hydrogen yield compared to that of the unidirectional (UD) operation. The effect of varying the inlet CH4:O2 feed ratio, the inlet velocity, and the inlet gas temperature is studied. The optimal feed ratio is found to be CH4:O2 = 1.15:1 with the feed at ambient room temperature. The effects of varying the reactor length and heat losses to the ambient are also investigated. In both these cases, the performance of the UD operation degrades significantly, whereas the performance of the RF operation is more robust to the variations in reactor size and heat losses. The issue of choosing the optimal switching time is also addressed. Switching the input and output ports near the natural timescale of reaction heat release is shown to provide the optimum yield. Through these results, design and operation guidelines based on simple timescale analysis have emerged. [ABSTRACT FROM AUTHOR]

A 1-D model for methane partial oxidation in a tubular microreactor is considered. This work is motivated by a recent report by Kikas et al. that experimentally demonstrated the possibility of autothermal generation of hydrogen by partial oxidation of methane in a tubular microreactor. The reactor consists off our cylindrical channels, each 500 microns in diameter, containing Pt/13%-Rh catalyst. Autothermal generation of hydrogen was possible in both unidirectional (UD) and reverse-flow (RF) operations of the reactor, with the RF operation providing better hydrogen yield and lower temperatures than those of the UD operation. Critical comparison of methane oxidation and reforming kinetics from the literature is performed. An analysis of the timescales of individual processes within the reactor is presented to gain fundamental insight into the reactor operation. Finally, the effect of radiation heat transfer is also considered, and it is found to play an important role for a shorter-size reactor. [ABSTRACT FROM AUTHOR]