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Abstract: Surface micro- and nanostructural modifications of dental and orthopedic implants have shown promising in vitro, in vivo and clinical results. Surface wettability has also been suggested to play an important role in osteoblast differentiation and osseointegration. However, the available techniques to measure surface wettability are not reliable on clinically relevant, rough surfaces. Furthermore, how the differentiation state of osteoblast lineage cells impacts their response to micro/nanostructured surfaces, and the role of wettability on this response, remain unclear. In the current study, surface wettability analyses (optical sessile drop analysis, environmental scanning electron microscopic analysis and the Wilhelmy technique) indicated hydrophobic static responses for deposited water droplets on microrough and micro/nanostructured specimens, while hydrophilic responses were observed with dynamic analyses of micro/nanostructured specimens. The maturation and local factor production of human immature osteoblast-like MG63 cells was synergistically influenced by nanostructures superimposed onto microrough titanium (Ti) surfaces. In contrast, human mesenchymal stem cells cultured on micro/nanostructured surfaces in the absence of exogenous soluble factors exhibited less robust osteoblastic differentiation and local factor production compared to cultures on unmodified microroughened Ti. Our results support previous observations using Ti6Al4V surfaces showing that recognition of surface nanostructures and subsequent cell response is dependent on the differentiation state of osteoblast lineage cells. The results also indicate that this effect may be partly modulated by surface wettability. These findings support the conclusion that the successful osseointegration of an implant depends on contributions from osteoblast lineage cells at different stages of osteoblast commitment. [Copyright &y& Elsevier]

Abstract: Thin liquid films can provide efficient means for heat and mass transfer by supporting a large rate of evaporation, while maintaining temperatures under saturation conditions. The use of nanoporous membranes establishes thin liquid films minimizing the possibility of dryout by exploiting capillary confinement of the fluid. In combination with gas jet impingement, this yields record high heat and mass fluxes. Consequently, for applications relying on efficient heat and mass transfer, such as, phase change cooling of electronics and membrane distillation of water, it is essential to identify and characterize all the underlying transport mechanisms affecting overall performance. A detailed computational analysis of heat and mass transfer is therefore carried out to predict the performance of thin film evaporation. Heat conduction and convection are both found crucial in determining the temperature distribution within the thin film region, which ultimately controls the rate of evaporation from the liquid–vapor interface. Furthermore, the effect of vapor transport from the liquid–vapor interface on overall performance is also assessed. The relative effects of these performance-governing parameters are discussed and quantitatively compared at different operating conditions. The results of the computational analysis are supported by comparison with experiments. [Copyright &y& Elsevier]

Abstract: Capture of carbon dioxide from distributed sources is often neglected as a viable solution to the global problem of CO2 emissions management. Small scale power plants, including those applicable to the transportation sector, can be designed to capture their CO2 exhaust stream, provided it is not heavily diluted with air. Liquefaction of carbon dioxide allows the captured CO2 to be stored densely, with a minimal energetic penalty and space requirement, until it can be permanently sequestered. In this short-term solution, the energetic penalty for CO2 capture can be further offset by exploiting novel energy conversion processes involving regeneration of the reaction product stream – a simple strategy that is not exploited in conventional systems. More importantly, in the long-term, as the renewable energy infrastructure is built up, the collected CO2 can be recycled into synthetic carbon-based liquid fuels which act as energy carriers in the sustainable carbon economy. [Copyright &y& Elsevier]

The flow of viscous incompressible micropolar fluid past a semi-infinite vertical porous plate is investigated with the presence of thermal radiation field, taking into account the progressive wave type of disturbance in the free stream. The effects of flow parameters and thermophysical properties on the flow and temperature fields across the boundary layer are investigated. The Rosseland approximation is used to describe radiative heat transfer in the limit of optically thick fluids. Numerical results of velocity profile of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. It is observed that, when the radiation parameter increases the velocity and temperature decrease in the boundary layer, whereas when Grashof number increases the velocity increases. [Copyright &y& Elsevier]

Energy efficiency, environmental impact, and quality of the final product in glass manufacturing depend, to a large extent, on foams formed on the surface of the molten glass and of the batch due to entrapment of gas bubbles generated by the batch fusion and refining chemical reactions during the melting process. Hence, understanding the mechanisms of foam formation as well as development of theoretical models for thermophysical and transport properties and heat, mass, and radiation transfer in glass foams are not only a problem of significant fundamental interest but also of tremendous practical impact. In this paper, the review of the current state-of-the-art in our understanding of glass foams is provided, including some of our recent results in modeling the dynamics of the foam growth and its steady-state thickness, prediction of gas diffusion through glass foams, and thermal radiative properties of glass foams. In addition, the new results on simulation of combined conduction and radiation heat transfer in glass foams and radiative transfer in primary (batch) foams are presented and discussed in some detail. The paper also presents practical means available for reducing foaming in glass melting and concludes with the discussion of unresolved problems and summary of the directions for the future work in the area. [Copyright &y& Elsevier]

Radiative transfer in a semitransparent hemispherical shell placed on an opaque surface is simple yet realistic representation of the heating process encountered in various materials processing applications ranging from metallurgical slag foaming to batch foams in glass melting to hollow bead fabrication. The objective of this paper is to develop fundamental understanding and predictive models for the apparent radiative properties of a hemispherical shell exposed to incident collimated radiation. Both analytical and numerical results are obtained and compared against each other for the purpose of validation of an analytical model. The study provides fundamental information on radiative transfer in a semitransparent hemispherical shell as well as presents an effective numerical algorithm to calculate the local intensity field and thus the local volumetric heating in the shell. [Copyright &y& Elsevier]

• Nano-electrosprayed droplets transfer momentum to ambient gas, producing a gas jet. • Thermodynamic performance metrics for nES gas jet production are established. • Increase in nES-driving electric field negatively impacts energy efficiency and effectiveness. • Smaller droplets and greater liquid flow rate yield improvement of all performance metrics. Nano-electrospray (nES) produces a plume of charged liquid droplets which have drag interactions with the surrounding gas after they are emitted from a source capillary. The resulting induced gas flow has often been considered unimportant, but we have demonstrated that a gas microjet of significant velocity up to 10s of m/s can be produced. In this work we present a thermodynamic framework that enables analysis of gas jet generation from electrosprays and introduce the important metrics for such analysis, effectiveness (a measure of momentum transfer from the electrosprayed aerosol to gas) and efficiency (a measure of energy conversion from electrical energy generating the electrospray to gas kinetic energy). This analytical framework is applicable to any two-phase flows consisting of discrete conservative-force-driven particles which exchange momentum with an inert, otherwise quiescent fluid medium to yield a co-flowing two-phase jet. We apply this framework to sprays of water from nano-electrospray emitters to demonstrate that increasing the applied electrical potential difference, increasing liquid mass flowrate, and decreasing droplet size all can increase electrospray induced gas jet strength, but only the latter two do so while also increasing the momentum transfer effectiveness and energy conversion efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nano-electrosprayed droplets transfer momentum to ambient gas, producing a gas jet. • Gas jets produced by nano-electrospray (nES) have a narrow, high-velocity core. • The high-velocity gas jet core is produced in the nES liquid jet breakup region. • Droplet size is a significant parameter affecting the velocity of the gas jet. Electrospray (ES) is production of a charged droplet plume that transits from an electrically biased supply capillary to a counter electrode under the influence of an electric field. Drag interactions with the surrounding gas decelerate the droplets while transferring the momentum from droplets to accelerate the surrounding gas, resulting in an induced gas flow. This work seeks to characterize the structure of the resulting gas jet and identify the key mechanisms defining the flow structure. The phenomenon of gas jets produced by momentum transfer from nano-electrospray (nES) plumes is explored with schlieren visualization, thermal anemometry, and numerical simulations. Schlieren visualization experiments provide information on the flow structure in support of simulation predictions, and the hot thermistor anemometry measurements of gas velocities outside the spray demonstrate quantitatively validated simulation results. The study reveals the formation of a moderately high velocity coaxial gas jet within the nES plume and provides insight into the overall flow structure of the induced flow. The multiphase electrohydrodynamic simulations enable numerical experimentation to explore the fundamental physics of coupled droplet-gas transport and the resulting flow structure. The simulations, confirmed by the experiments, reveal gas jetting induced by nES with a narrow (sub hundred micrometers in diameter) core originating from the nES liquid-jet breakup region and a surrounding larger-in-extent zone (several hundred micrometers in diameter) of lower velocity gas flow within the electrospray plume. This behavior is due to nES ejecting a stream of droplets from the tip of a narrow liquid cone-jet, where the combined effect of many small droplets transferring momentum to a confined region of gas yields a narrow but high-velocity gas stream. The micro-jets produced by nES have practical utility for mass spectrometry, 3D printing and fabrication, and thermal management. [Display omitted] [ABSTRACT FROM AUTHOR]

In-process monitoring and control of biomanufacturing workflows remains a significant challenge in the development, production, and application of cell therapies. New process analytical technologies must be developed to identify and control the critical process parameters that govern ex vivo cell growth and differentiation to ensure consistent and predictable safety, efficacy, and potency of clinical products. This study demonstrates a new platform for at-line intracellular analysis of T-cells. Untargeted mass spectrometry analyses via the platform are correlated to conventional methods of T-cell assessment. Spectral markers and metabolic pathways correlated with T-cell activation and differentiation are detected at early time points via rapid, label-free metabolic measurements from a minimal number of cells as enabled by the platform. This is achieved while reducing the analytical time and resources as compared to conventional methods of T-cell assessment. In addition to opportunities for fundamental insight into the dynamics of T-cell processes, this work highlights the potential of in-process monitoring and dynamic feedback control strategies via metabolic modulation to drive T-cell activation, proliferation, and differentiation throughout biomanufacturing. [ABSTRACT FROM AUTHOR]

Combined reaction–separation processes are a widely explored method to produce hydrogen from endothermic steam reforming of hydrocarbon feedstock at a reduced reaction temperature and with fewer unit operation steps, both of which are key requirements for energy efficient, distributed hydrogen production. This work introduces a new class of variable volume batch reactors for production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. It incorporates a CO 2 adsorbent and a selectively permeable hydrogen membrane for in situ removal of the two major products of the reversible steam methane reforming reaction. Thermodynamic analysis is employed to define an envelope of ideal reactor performance and to explore the tradeoff between thermal efficiency and hydrogen yield density with respect to critical operating parameters, including sorbent mass, steam to methane ratio and fraction of product gas recycled. Particular attention is paid to contrasting the variable volume batch-membrane reactor approach to a conventional fixed bed reaction–separation approach. The results indicates that the proposed reactor is a viable option for low temperature distributed production of hydrogen from methane, the primary component of natural gas feedstock, motivating a detailed study of reaction/adsorption kinetics and heat/mass transfer effects. [ABSTRACT FROM AUTHOR]

Abstract: The development of an absorption based miniature heat pump system is motivated by the need for removal of increasing rates of heat from high performance electronic chips such as microprocessors. The goal of the present study is to keep the chip temperature near ambient temperature, while removing 100W of heat load. Water/LiBr pair is used as the working fluid. A novel dual micro-channel array evaporator is adopted, which reduces both the mass flux through each micro-channel, as well as the channel length, thus reducing the pressure drop. Micro-channel arrays for the desorber and condenser are placed in intimate communication with each other using a hydrophobic membrane. This acts as a common interface between the desorber and the condenser to separate the water vapor from LiBr solution. The escaped water vapor is immediately cooled and condensed at the condenser side. For direct air cooling of condenser and absorber, offset strip fin arrays are used. The performance of the components and the entire system is numerically evaluated and discussed. [Copyright &y& Elsevier]

Understanding two-phase convective heat transfer under extreme conditions of high heat and mass fluxes and confined geometry is of fundamental interest and practical significance. In particular, next generation electronics are becoming thermally limited in performance, as integration levels increase due to the emergence of ‘hotspots’ featuring up to ten-fold increase in local heat fluxes, resulting from non-uniform power distribution. An ultra-small clearance, 10 μm microgap, was investigated to gain insight into physics of high mass flux refrigerant R134a flow boiling, and to assess its utility as a practical solution for hotspot thermal management. Two configurations – a bare microgap, and inline micro-pin fin populated microgap – were tested in terms of their ability to dissipate heat fluxes approaching 1.5 kW/cm 2 . Extreme flow conditions were investigated, including mass fluxes up to 3000 kg/m 2 s at inlet pressures up to 1.5 MPa and exit vapor qualities approaching unity. Dominant flow regimes were identified and correlated to two phase heat transfer coefficients which were obtained using model-based data reduction for both device configurations. The results obtained were compared to predictions using correlations from literature, with the maximum heat transfer coefficient reaching 1.5 MW/m 2 K in the vapor plume regime in the case of the finned microgap. [ABSTRACT FROM AUTHOR]

The presence of variable heat fluxes, such as localized hotspots in integrated circuit (IC) architectures poses a key challenge for thermal management of existing (2D) and emerging three-dimensionally (3D) stacked chips. The use of conventional microchannel or uniform pin fin arrays for microfluidic cooling do not provide adequate surface area for heat transfer in the vicinity of regions of concentrated high power (hotspots), and therefore significant temperature gradients might arise in such zones. In the present investigation, the concept of using a single microfluidic loop for the combined and efficient cooling of hotspot and moderate power (background) areas is proposed, experimentally demonstrated, and supported by a comprehensive numerical model. Two different thermal device vehicles (TDVs) are considered for a range of operating conditions, in which the surface area is locally increased by clustering a dense array of pin fins in the hotspot region for one configuration, while for the other the clustering is uniform in the spanwise direction. De-ionized (DI) water is used as the coolant through a silicon (Si) microgap with 200 μm spacing; the hotspot heat flux is varied from 250 to 750 W/cm 2 , while the background heat flux is fixed at 250 W/cm 2 . Results indicate the capability of the proposed designs to keep the maximum temperature of the combined device below 65 °C for an inlet water temperature of 21.3 °C, with moderate temperature gradients and pressure drop. In addition, a robust computational fluid dynamics/heat transfer (CFD–HT) model capable of predicting spatially resolved temperature fields arising from heterogeneous heating is validated with relevant experimental data. Detailed benchmark simulations are provided, so they can be reproduced and used for reference in numerical studies with variable pin fin densities. The described methodology represents a cost-effective thermal modeling technique that may be applicable to virtually any type of heat flux distribution or power map, and IC architecture. [ABSTRACT FROM AUTHOR]

• Opaque, mesoscale surfaces are capable of raising and lowering apparent emissivity. • External emitting surfaces raise the apparent emissivity. • Reradiating surfaces lower the apparent emissivity. • Combining different materials, geometries allows wide range of apparent properties. • Analytic relationships well suited to machine learning optimization. In this study, a method for using arrays of mesoscale structures to modify the apparent optical properties of an opaque composite surface has been theoretically demonstrated to both raise and lower the apparent emissivity as compared to the intrinsic properties of the constitutive materials. For design problems where thermomechanical and optical material properties are both of importance, mesoscale surface structuring can greatly expand the design space. Analysis via the net radiosity method herein illustrates the ability to achieve a wide range of spectral apparent optical properties. Notably, a hexagonal array of spheres on a planar surface can raise the apparent emissivity of a planar surface by 50%. Conversely, a hexagonal enclosure of reradiating surfaces, realized by thin adiabatic walls, can reduce the apparent emissivity of a blackbody by half. As this method of modifying apparent optical properties utilizes structures much larger than the wavelengths of interest, the relationship between intrinsic planar emissivity, geometry, and apparent emissivity can be computed semi-analytically at low computational expense. Passive solar cooling, thermophotovoltaic cells, aerodynamic surfaces exposed to intense heating, and solar absorbers are presented as case studies that could benefit from the use of mesoscale structures on opaque surfaces to modify the apparent optical properties. [ABSTRACT FROM AUTHOR]

A direct liquid fuel injection/variable volume reactor integrated with a hydrogen selective membrane (CHAMP-DDIR) has been recently shown to be a promising new concept for hydrogen production in portable and distributed applications. The CHAMP-DDIR reactor performance has been analyzed using a simplified transport model with which conditions for maximum performance, e.g. highest volumetric power density, were identified. A prototype reactor demonstrated the ability to realize performance improvement, while also indicating a need for more a rigorous model for accurate exploration of the design and operation space. In this paper, we present a comprehensive reactor model which carefully considers the effects of heat and mass transfer, including rigorous treatment of multi-component species transport. The model is validated against experimental results through comparison of predicted and measured hydrogen production rate, reactor pressure, and temperature. The experimentally validated model is used to identify the relationship between CHAMP-DDIR design and operating parameters and the rate-limiting processes that govern reactor output. In addition, effects of heat and mass transfer limitations on CHAMP-DDIR performance are investigated by comparing the predictions among multiple cases with increasing level of complexity used for modeling the transport phenomena within the reactor. [ABSTRACT FROM AUTHOR]

A novel dynamically-controlled membrane batch reactor, which combines the variable volume operation of CHAMP (CO 2 /H 2 Active Membrane Piston) with the direct injection of liquid fuel of DDIR (Direct Droplet Impingement Reactor) for enhanced power density, is demonstrated and experimentally characterized in this study. A laboratory-scale CHAMP-DDIR, consisting of a variable volume piston-cylinder reactor chamber and an actively-controlled micro injector for liquid fuel atomization, is used with a Pd–Ag foil membrane and Cu/ZnO/Al 2 O 3 catalyst to steam reform methanol for hydrogen generation. Two modes of CHAMP-DDIR operation, pulse-modulated fuel injection and batch reaction with dynamically-adjusted reactor volume, were investigated, and their performance was quantified using metrics such as hydrogen yield and volumetric power density, and compared with those for a baseline operation (single fuel injection with fixed reactor volume). The experimental results showed that the residence time for the same hydrogen yield can be reduced by compressing the reactor volume during the conversion cycle. The residence time reduction was primarily as a result of higher hydrogen partial pressure in the reactor chamber and thus higher rates of hydrogen permeation. In addition, pulse-modulated fuel injection experiments revealed that a significant reduction in required reactor volume can be achieved with multi-shot split fuel introduction. Both the reduction in required cycle time and the reduction in required reactor volume increase the volumetric power density of CHAMP-DDIR. The demonstrated power density enhancement achieved through the dynamic compression of reactor volume was 17%, and the enhancement achieved through time-modulated fuel introduction was 38% (for 85% hydrogen yield efficiency and under the constraints of the same maximum operating pressure and total amount of fuel). [ABSTRACT FROM AUTHOR]

Thermodynamics of an ionic-liquid (IL) based absorption refrigeration system has been numerically analyzed. It provides an alternative to the normally toxic working fluids, such as the ammonia in conventional absorption systems. The use of ILs also eliminates crystallization and metal-compatibility problems of the water/LiBr system. Mixtures of refrigerants and imidazolium-based ILs are theoretically explored as the working fluid pairs in a miniature absorption refrigeration system, so as to utilize waste-heat to power a refrigeration/heat pump system for electronics cooling. A non-random two-liquid (NRTL) model was built and used to predict the solubility of the mixtures. Saturation temperatures at the evaporator and condenser were set at 25 °C and 50 °C, respectively, with the power dissipation of 100 W. Water in combination with [emim][BF4] (1-ethyl-3-methylimidazolium tetrafluoroborate) gave the highest coefficient of performance (COP) around 0.9. The refrigerant/IL compatibility indicated by the circulation ratio, alkyl chain length of the IL, and thermodynamic properties of the refrigerants, such as latent heat of evaporation were proven to be important factors in determining the performance of the absorption system. The negative effect of high viscosity was mitigated by dilution of the IL with the refrigerant and the use of slightly larger microfluidic channel heat exchangers. [ABSTRACT FROM AUTHOR]

Abstract: Electron beam induced dissociation (EBID) of residual hydrocarbons is a common contamination problem in electron microscopy. Formation of amorphous carbon thin films, dots, rings, and complex three-dimensional (3D) structures has been documented. In recent years there has been a renewed interest in utilization EBID of residual hydrocarbons for nanomanufacturing and metrology. With the increase and the diversification of EBID applications, ability for an a priori prediction of the appropriate deposition settings (such as electron beam current, diameter, and energy) that would result in a desired deposit size and geometry is becoming increasingly important. Toward this end, we report how simulations can be used to quantitatively predict the complex shape and non-linear dynamics of secondary ring-type microstructures formed around nanopillar deposits. The deposition experiments were performed on a Si(100) substrate for different electron beam energies and currents. Deposit shape and transient evolution were characterized using atomic force microscopy and critically compared against simulations results. [Copyright &y& Elsevier]

Abstract: The boundary integral method (BIM) is one of the most efficient numerical methods for solving boundary-value problems. This methodology is becoming increasingly recognized in analytical chemistry for theoretical characterization of microelectrodes and quantitative electroanalysis. This paper reviews the fundamentals of the BIM and uses several electroanalytical case studies to discuss the advantages, limitations, and implementation difficulties from a practitioner’s viewpoint. [Copyright &y& Elsevier]