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Thermocline tanks have been considered as an alternative to traditional two-tank molten salt thermal storage in concentrating solar power systems due to their potential for cost reduction. One concern for thermocline usage is thermal ratcheting caused by the internal rock bed deformation during cyclic operation and significant temperature fluctuations. Thermal ratcheting studies have been performed in the literature to identify the possibility of tank rupture. However, these studies numerically modeled the ratcheting behavior utilizing bed properties that have never been measured for the materials used in thermocline storage systems. This work presents triaxial test data quartzite and silica thermocline filler materials to better inform future investigations of thermal ratcheting. Molten salt is replaced with water as the interstitial fluid due to similarity in dimensionless numbers and to accommodate room temperature measurement. Material property data for cohesion, dilatancy angle, internal angle of friction, Young's modulus, Poisson's ratio, and bulk modulus are presented for 0.138-0.414 MPa confining pressure. The material properties are then compared to those assumed in the literature to comment on the potential impact of this property data relative to thermal ratcheting. [ABSTRACT FROM AUTHOR]

This paper provides a review of high-efficiency thermodynamic cycles and their applicability to concentrating solar power systems, primarily focusing on high-efficiency single and combined cycles. Novel approaches to power generation proposed in the literature are also highlighted. The review is followed by analyses of promising candidates, including regenerated He-Brayton, regenerated CO2-Brayton, CO2 recompression Brayton, steam Rankine, and CO2–ORC combined cycle. Steam Rankine is shown to offer higher thermal efficiencies at temperatures up to about 600°C but requires a change in materials for components above this temperature. Above this temperature, CO2 recompression Brayton cycles are shown to have very high thermal efficiency, potentially even exceeding 60% at 30MPa maximum pressure and above 1000°C maximum temperature with wet cooling. An estimate of a combined receiver and power cycle operating temperature is provided for the cycles considered and compared to the traditional approach of optimization based on the Carnot efficiency. It is shown that the traditional approach to optimizing the receiver and turbine inlet temperatures based on Carnot is generally not sufficient, leading to an optimum temperature shift of more than 100°C from the Carnot case under various conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews central receiver designs for concentrating solar power applications with high-temperature power cycles. Desired features include low-cost and durable materials that can withstand high concentration ratios (~1000 suns), heat-transfer fluids that can withstand temperatures >650°C, high solar absorptance, and low radiative and convective heat losses leading to a thermal efficiency >90%. Different receiver designs are categorized and evaluated in this paper: (1) gas receivers, (2) liquid receivers, and (3) solid particle receivers. For each design, the following information is provided: general principle and review of previous modeling and testing activities, expected outlet temperature and thermal efficiency, benefits, perceived challenges, and research needs. Emerging receiver designs that can enable higher thermal-to-electric efficiencies (50% or higher) using advanced power cycles such as supercritical CO2 closed-loop Brayton cycles include direct heating of CO2 in tubular receiver designs (external or cavity) that can withstand high internal fluid pressures (~20MPa) and temperatures (~700°C). Indirect heating of other fluids and materials that can be stored at high temperatures such as advanced molten salts, liquid metals, or solid particles are also being pursued, but challenges include stability, heat loss, and the need for high-temperature heat exchangers. [Copyright &y& Elsevier]

Highlights: [•] Molten-salt thermocline tanks offer low-cost thermal energy storage for concentrating solar power plants. [•] A new thermocline tank model is developed to provide comprehensive thermal simulation at low computational cost. [•] The thermocline model is incorporated into a system model to study storage performance over long-term plant operation. [•] Yearlong simulation of a power tower plant indicates excellent storage performance with the thermocline tank concept. [ABSTRACT FROM AUTHOR]

Highlights: [•] Modeling and experimental data are presented and compared. [•] Results include transient response of a sCO2 Brayton to reduced thermal input. [•] Benchmarking data for steady state operation is tabulated. [•] Areas of necessary research for successful implementation of sCO2 Brayton. [Copyright &y& Elsevier]

Abstract: Implementation of molten salt compounds as the heat transfer fluid and energy storage medium provides specific benefits to energy collection and conversion. Nitrate salts have been identified as a strong candidate for energy transfer and storage and have been demonstrated for use in these applications over time. As nitrate salts have solidification temperatures above ambient, concern for recovery from salt freezing events has instigated efforts to understand and predict this behavior. Accurate information of salt property behavior in the solid-phase is necessary for understanding recovery from a freeze event as well as for phase change thermal energy storage applications. Thermal and mechanical properties for three representative salts (solar salt, HITEC salt, and a Na–K–Li–Ca nitrate salt; spanning the range of liquidus temperatures from approximately 90–240°C), have been obtained. These properties include: specific heat, coefficient of thermal expansion, thermal conductivity, latent heat of fusion, compressive strength, tensile strength, Young’s modulus and Poisson’s ratio. Specific heat, thermal conductivity and latent heat of fusion were measured using differential scanning calorimetry. Temperature was not observed to have a significant effect on tensile strength using an indirect tensile test (Brazilian test). Peak stress and Young’s modulus (both from unconfined compressive strength testing) were shown to decrease while Poisson’s ratio increased with increasing temperature. [Copyright &y& Elsevier]

• Initial heat rate increases with wettability. • Heat flux increases with Reynolds number. • Significantly lower average maximum heat flux on superhydrophobic surfaces. • Temperature has negligible effect on heat transfer on superhydrophobic surfaces. Superhydrophobic (SH) surfaces possess desirable anti-fouling properties due to low wettability, but have also been shown to reduce heat transfer to subcooled water in impinging jet scenarios. In this work, superheated silicon substrates with varying wettability (hydrophilic or HPi, hydrophobic or HPo, SH) are quenched by an impinging water jet, where the substrate temperature is above the saturation temperature. Silicon wafers are either oxidized to create HPi surfaces, coated with Teflon to make the surface HPo, or plasma-etched and coated to create the necessary micro-texture for SH conditions. All wafers are integrated with an electric resistance heater and then heated to temperatures of 200–320 ∘ C before impingement with an axisymmetric room temperature water jet of varying specified flow rates yielding jet Reynolds numbers between 6000 and 18,000. High-speed visual data is collected, showing how the lamellar liquid contact region, limited by thermal breakup due to boiling, grows radially as the surface cools to temperatures below saturation. This data is correlated to temperature data recorded on the back side of the wafer using a thermal camera. Results of this study confirm previous conjecture that surface wettability can alter maximum heat flux, which is quantified here for the described scenario by up to 40%, and can also affect jet thin film spreading by up to 50%. Increasing initial surface temperature decreases thin film spreading rate on all surfaces, and increases heat transfer on all but the SH surfaces. Increasing Reynolds number yields an increase in heat flux, and affects both the thin film spreading rate as well as the maximum radius of the thin film region. [ABSTRACT FROM AUTHOR]

Thermal diffusion measurements on polymethylmethacrylate-coated Si substrates using heated atomic force microscopy tips were performed to determine the contact resistance between an organic thin film and Si. The measurement methodology presented demonstrates how the thermal contrast signal obtained during a force-displacement ramp is used to quantify the resistance to heat transfer through an internal interface. The results also delineate the interrogation thickness beyond which thermal diffusion in the organic thin film is not affected appreciably by the underlying substrate. [ABSTRACT FROM AUTHOR]

We report noise and detection limitations in cantilever-based immunomagnetic biosensors. A differential cantilever system with sensing and control arms was used whereby the control arm was passivated with bovine serum albumin (BSA) and the sensing arm was functionalized with biotin-BSA. Streptavidin-coated magnetic beads were exposed to cantilever arms. An oscillatory magnetic field induced a magnetic force on the beads which caused a relative deflection of the sensing arm. Increasing the excitation frequency suppressed the 1/f noise by 100-fold, resulting in a deflection resolution of 0.065 Å in air. [ABSTRACT FROM AUTHOR]

Combining the resolution of conventional gas chromatography systems with the size factor of microGC systems is important for improving the affordability and portability of high performance gas analysis. Recent work has demonstrated the feasibility of high resolution separation of gases in a benchtopscale short column system by controlling thermal gradients through the column. This work reports a microfabricated thermally controllable gas chromatographic column with a small footprint (approximately 6.25 cm2). The design of the 20 cm column utilizes 21 individually controllable thin film heaters and conduction cooling to produce a desired temperature profile. The reported device is capable of heating and cooling rates exceeding 8000 °C/min and can reach temperatures of 350 °C. The control methods allow for excellent disturbance rejection and precision to within +/− 1 °C. Each length of the column between heaters was demonstrated to be individually controllable and displayed quadratic temperature profiles. This paper focuses on the fabrication process and implementation of the thermal control strategy. [2019–0113] [ABSTRACT FROM AUTHOR]

This work investigates the electrochemical dynamics and performance of additively manufactured composite electrolytes for resistive switching. Devices are comprised of a Ag/AgI–Al2O3/Pt stack, where the solid state electrolyte is additively manufactured using extrusion techniques. AgI–Al2O3 composite electrolytes are characterized by x-ray diffraction and electrochemical impedance spectroscopy. The ionic conductivities of the electrolytes were measured for different concentrations of Al2O3, observing a maximum conductivity of 4.5 times the conductivity of pure AgI for composites with 20 mol. % Al2O3. There was little change in activation energy with the addition of Al2O3. Setting the Ag layer as the positive electrode and the Pt layer as the negative electrode, a high conductivity state was achieved by applying a voltage to electrochemically establish an electrically conducting Ag filament within the solid state AgI–Al2O3 electrolyte. The low conductivity state was restored by reversing this applied voltage to electrochemically etch the newly grown Ag filament. Pure AgI devices switch between specific electrical resistivity states that are separated by five orders of magnitude in electrical conductivity. Endurance tests find that the AgI resistive switches can transition between a low and high electrical conductivity state over 8500 times. Composite AgI–Al2O3 resistive switches formed initial Ag filaments significantly faster and also demonstrated two orders of magnitude separation in resistivity when cycling for 1600 cycles. [ABSTRACT FROM AUTHOR]

Thermal management systems for space equipment commonly use static solutions that do not adapt to environmental changes. Dynamic control of radiative surface properties is one way to respond to environmental changes and to increase the capabilities of spacecraft thermal management systems. This paper documents an investigation of the extent to which origami-inspired surfaces may be used to control the apparent absorptivity of a reflective material. Models relating the apparent absorptivity of a radiation shield to time-dependent surface temperatures are presented. Results show that the apparent absorptivity increases with increasing fold density and indicate that origami-inspired designs may be used to control the apparent radiative properties of surfaces in thermal management systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The life cycle of steam-exploded (SE) biomass as a fuel source is reviewed. • All the unit operations of the steam explosion process are discussed in detail. • Differences between SE pellets with white and torrefied pellets are summarized. • Economic analysis, lifecycle assessment, and future research needs are examined. • SE product properties and their uses in milling and combustion systems are discussed. With the rapid decarbonization of the energy industry, a viable alternative to coal in power plants is essential. Two important fuel properties to be considered in a coal substitute are high energy density and grindability. Steam-exploded (SE) biomass pellets have characteristics that are sufficiently similar to coal in both these respects. Steam explosion is a hydrothermal treatment method which violently ruptures the lignocellulosic structure of the biomass, and makes it more conducive to milling and combustion. Included herein is a review of the unit operations, advantages and disadvantages compared to torrefaction and regular pelletizing, economic analysis, lifecycle assessment, and research needs of the SE process. The SE process improves the tensile strength, durability, and water-resistance of biomass, which alleviates transportation costs and mitigates degradation and fire hazards during fuel storage. SE can be applied to a range of biomass resources including agricultural residue, industrial waste, forest residue, and fast-growing crops. Instances where SE biomass has been co-milled and co-fired with coal in industrial-scale pulverizers and boilers are summarized. The combustion of steam-exploded biomass reduces particulate matter, NO x , and SO 2 emissions compared to coal combustion. The key conclusion is that steam-exploded 'black pellets' can be used as a sustainable and low-polluting fuel in existing coal-fired electric utility boilers without retrofitting existing equipment. The uniqueness of this review is that it presents a complete summary of relevant industrial operations, from the collection to the combustion of steam-exploded biomass, and offers insight into the technical and commercial challenges facing the biomass treatment industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biomass and coal blends were co-fired to study synergistic SO 2 emission reduction. • Calcium and potassium in the biomass ash absorbed the SO 2 from the flue gas. • Sulfur retained in ash was low for pure coal and biomass and high for middle blends. • FactSage thermodynamic simulation results matched well with the experimental results. • Co-firing biomass with coal can lower the flue gas desulfurization costs. The objective of this study was to understand the synergistic effect of sulfur dioxide (SO 2) emission reduction during the combustion of biomass-coal blends in comparison to pure coal by recording the gaseous SO 2 concentrations, analyzing the composition of combustion ash by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), and simulating and verifying the fate of sulfur by a thermodynamic equilibrium software (FactSage). In Set A experiments, five combinations of coal and steam-exploded biomass (100/0, 75/25, 50/50, 25/75, 0/100 in percentages by mass) were co-fired in a 1.5 MW th pilot-scale combustor. In Set B, pure coal (100/0) and an 85/15 percent mass blend of coal and torrefied biomass were co-fired in a 471 MW e utility boiler. Woody biomass contains lower amounts of sulfur compared to coal and the linear lowering of SO 2 emissions as a result of co-firing is called the dilution effect. For Set A tests, FactSage predicted, and ash analysis confirmed that calcium was primarily responsible for the synergistic emission reduction (beyond dilution effect) in all the blends, except in pure biomass, where potassium was responsible. During pure coal combustion, 41.1% of the sulfur in the system was absorbed in the ash, compared to 97.0% during pure biomass testing. In Set B tests, the 85/15 coal-biomass blend, showed a 28.1% reduction in SO 2 emissions along with a 22.1% reduction in the lime slurry utilization at flue gas desulfurization (FGD) towers compared to pure coal, which is equivalent to saving 7.4 L of lime slurry per MW e -hour. The results suggest that blending woody biomass with coal can help coal-fired utility boilers meet environmental emission standards and reduce desulfurization costs. These results are important since the current literature is deficient in research conducted at suspension-fired full-scale boilers to reduce SO 2 emissions by co-firing coal and biomass blends. [ABSTRACT FROM AUTHOR]

• Radiative fins with dynamic geometry can influence heat transfer rates in real time. • Self-irradiation decreases turn-down ratio but increases fin efficiency. • Fin efficiency is greatest for collapsed fins and smallest for extended fins. • A turn-down ratio of three or greater is possible with dynamic radiative fins. Efficient heat transfer is critical in the design and optimization of thermal control systems. Static radiative heat exchangers are often simple and reliable systems but typically cannot be adapted to environmental changes. Adaptable radiative heat exchangers can be adjusted in response to variations in the thermal environment or operating conditions and have the potential for increased efficiency and reduced cost. Dynamic control of a radiative heat exchanger is possible through geometric manipulation of a segmented, self-irradiating fin, consisting of rigid panels that are linked by thermal hinges in an accordion arrangement. In this paper, a numerical model is described to predict the temperature profile and efficiency of a radiative heat exchanger, accounting for conduction and self-irradiation. Governing equations are cast in terms of the conduction-radiation interaction parameter, surface emissivity, actuation angle, and the thermal conductance of the hinges linking the panels. Results indicate that a turn-down ratio (largest possible heat rate divided by smallest possible heat rate) of greater than three is possible for realistic panel geometries and materials. Self-irradiation decreases the turn-down ratio, and there is evidence that an optimal number of rigid panels exists for any combination of panel geometry and device temperature. The maximum efficiency occurs when the plates are in the collapsed position, but the heat rate is at a minimum in this configuration. Finally, the properties and geometry of the plates are shown to have a more significant effect on the turn-down ratio than the properties of the thermal hinges. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of drop impingement and thermal atomization on hydrophobic and superhydrophobic (SH) surfaces. Superhydrophobic surfaces having both microscale and nanoscale geometry are considered. Microscale SH surfaces are coated with a hydrophobic coating and exhibit micropillars and cavities which are classified using the surface solid fraction and center to center pitch. The solid fraction and pitch values explored in this study range from 0.05-1.0 and 8-60 μm respectively. Nanoscale textured surfaces are created by applying a blanket layer of carbon nanotubes. Both types of surfaces are further classified by a temperature jump length (λ T). All experiments were conducted at We = 85. Results of atomization as a function of time for the impingement event are provided for several surfaces of varying surface geometry, surface temperature, and temperature jump length. Nanoscale SH surfaces are shown to completely suppress atomization at all conditions explored. Results of the maximum atomization that occurred on a given surface are also shown as a function of the surface temperature. The surface temperature at which the maximum atomization occurs varies with surface geometry. Further, the time after impact when the maximum atomization occurs is also a function of the SH surface parameters. In general, the maximum atomization magnitude and the surface temperature at which maximum atomization occurs each decrease with increasing λ T. Further, the time when maximum atomization occurs increases with increasing λ T. • Drop impingement on superheated superhydrophobic surfaces is explored. • Time varied atomization magnitude is quantified using an image processing technique. • Test surfaces include micro and nanostructured superhydrophobic surfaces. • Atomization is completely suppressed on nanoscale superhydrophobic surfaces. • Atomization data is generalized using a temperature jump length. [ABSTRACT FROM AUTHOR]

Origami tessellations have been proposed as a mechanism for control of radiative heat transfer through the use of the cavity effect. This work explores the impact of a changing projected surface area and varying apparent radiative properties on the net radiative heat transfer of an accordion fold comprised of V-grooves. The net radiative heat transfer of an accordion tessellation is obtained by a thermal energy balance at the cavity openings with radiative properties of the cavities given as a function of various cavity parameters. Results of the analytical model are experimentally confirmed. An accordion tessellation, constructed of stainless-steel shim stock, is positioned to achieve a specified fold angle and placed in a vacuum environment while heated by Joule heating. A thermal camera records the apparent temperature of the cavity openings for various fold angles. Results are compared to apparent temperatures predicted with the analytical model. Analytically and experimentally obtained temperatures agree within 5% and all measurements fall within experimental uncertainty. For diffusely irradiated surfaces, the decrease in projected surface area dominates, causing a continuous decrease in net radiative heat transfer for a collapsing accordion fold. Highly reflective specular surfaces exposed to diffuse irradiation experience large turn-down ratios (7.5× reduction in heat transfer) in the small angle ranges. Specular surfaces exposed to collimated irradiation achieve a turn down ratio of 3.35 between V-groove angles of 120deg and 150deg. The approach outlined here may be extended to modeling the net radiative heat transfer for other origami tessellations. [ABSTRACT FROM AUTHOR]

Highlights • Superhydrophobic surfaces act as nucleation sites for mass transport. • Nucleating bubble behavior depends on the underlying micro-structure. • Large bubbles form and impede heat transfer. Abstract This work experimentally explores sub-boiling pool nucleation on micro-structured superhydrophobic surfaces. All surfaces tested were submerged in a 20 mm deep pool of water and heated from below to maintain a constant surface temperature, while the side walls of the pool were insulated, and the top was covered. Three thermocouples positioned in the pool obtain the average pool temperature. A heat flux sensor is placed directly beneath the surface to measure the heat flux supplied to the pool. Free convection heat transfer coefficients are obtained for the sub-boiling temperature range of 40–90 °C. Six surface types are studied: smooth hydrophilic, smooth hydrophobic, superhydrophobic with rib/cavity structures, superhydrophobic with rib/cavity structures and additional sparsely spaced ribs to close off the cavities, circular posts, and circular holes. It is found that structured superhydrophobic surfaces provide cavities for nucleation to occur. More dissolved air effervesces from the water as the surface temperature increases due to an increased level of supersaturation and convection. The nucleation leads to large air bubble formations that reduce the overall convection coefficient when compared to the smooth surfaces. For the rib/cavity structured surfaces, the bubbles form in an anisotropic manner and are aligned with the surface structure. More bubbles are observed on the superhydrophobic surfaces where the cavities are bounded. Since water's ability to dissolve air is dependent on temperature, heat and mass transfer cannot be treated independently on any of the superhydrophobic surfaces studied here. [ABSTRACT FROM AUTHOR]

Vertically aligned carbon nanotube array (VANTA) coatings have recently garnered significant attention due in part to their unique material properties including light absorption, chemical inertness, and electrical conductivity. Herein we report the first use of VANTAs grown via chemical vapor deposition in a 2D interdigitated electrode (IDE) footprint with a high height-to-width aspect ratio (3:1 or 75:25 µm). The VANTA-IDEs were functionalized with an antibody (Ab) specific to the human cancerous inhibitor PP2A (CIP2A)—an oncoprotein that is associated with a variety of malignancies such as oral, breast, and multiple myeloma cancers. The resultant label-free immunosensor was capable of detecting CIP2A across a wide linear sensing range (1−100 pg/mL) with a detection limit of 0.24 pg/mL within saliva supernatant—a range that is more sensitive than the corresponding CIP2A enzyme linked immunosorbent assay (ELISA). These results help pave the way for rapid cancer screening tests at the point-of-care (POC) such as for the early-stage diagnosis of oral cancer at a dentist's office. [ABSTRACT FROM AUTHOR]

Multiple reflections in a cavity geometry augment the emission and absorption of the cavity opening relative to a flat surface in a phenomenon known as the cavity effect. The extent of the cavity effect is quantified using apparent absorptivity and apparent emissivity. Analysis of complicated thermal systems is simplified through application of apparent radiative properties to cavity geometries. The apparent radiative properties of a specularly-reflecting, gray, isothermal V-groove have been derived analytically, but these results have not been validated experimentally or numerically. Additionally, the model for apparent absorptivity of an infinite V-groove subjected to partial illumination in the presence of collimated irradiation is not available. In this work, the following existing models for a specularly-reflecting V-groove are collected into a single source: (1) the apparent absorptivity of a diffusely irradiated V-groove, (2) the apparent emissivity of an isothermal V-groove and (3) the apparent absorptivity of a V-groove subject to collimated irradiation with full-illumination. Further, a new analytical model is developed to predict the apparent absorptivity of an infinite V-groove subject to collimated irradiation with partial-illumination. A custom, Monte Carlo ray tracing solver is used to predict the apparent radiative properties for all cases as a means of numerical verification by comparing the ray tracing data with the results from the new model in this work and the previously existing models. For diffuse irradiation, the analytical model and ray tracing data show excellent agreement with an average discrepancy of 4.4 × 10 −4 , verifying the diffuse-irradiation analytical model. Similar agreement is found for collimated irradiation, where the full and partial illumination models indicate average discrepancies of 4.9 × 10 −4 and 4.6 × 10 −4 when compared with ray tracing data. [ABSTRACT FROM AUTHOR]

This work experimentally studies the effects of single wall heating on laminar flow in a high-aspect ratio superhydrophobic microchannel. When water that is saturated with air is used as the working liquid, the non-wetted cavities on the superhydrophobic surfaces act as nucleation sites and allow air to effervesce out of the water and onto the surface when heated. Previous works in the literature have only considered the opposite case where the water is undersaturated and absorbs air out the cavities for a microchannel setting. The microchannel considered in this work consists of a rib/cavity structured superhydrophobic surface and a glass surface separated by spacers. The microchannel is 60 mm long by 14 mm wide and two channel heights of nominally 183 μm and 366 μm are explored. The superhydrophobic side is in contact with a heated aluminum block and a camera is used to visualize the flow through the glass side. Thermocouples are embedded in the aluminum to record the temperature profile along the length of the channel. Temperatures are maintained below the boiling temperature of the working liquid. The friction factor-Reynolds product ( fRe ) is obtained via pressure drop and volumetric flow-rate measurements. Five surface types/configurations are investigated: smooth hydrophilic, smooth hydrophobic, superhydrophobic with ribs perpendicular to the flow, superhydrophobic with ribs parallel to the flow, and superhydrophobic with ribs parallel to the flow with several breaker ridges perpendicular to the flow. The surface type/configuration has a significant impact on the mass transport dynamics. For surfaces with closed cell micro-structures, large bubbles eventually form and adversely affect fRe and lead to higher temperatures along the channel. When degassed water is used, no bubble nucleation is observed and the air initially trapped in the superhydrophobic cavities is quickly absorbed by the water. [ABSTRACT FROM AUTHOR]

The use of carbon nanotubes to create superhydrophobic coatings has been considered due to their ability to offer a relatively uniform nanostructure. However, carbon nanotubes (CNTs) may be considered delicate with a typical diameter of tens of nanometers for a multi-walled CNT; as-grown carbon nanotubes often require the addition of a thin-film hydrophobic coating to render them superhydrophobic. Furthermore, fine control over the diameter of the as-grown CNTs or the overall nanostructure is difficult. This work demonstrates the utility of using carbon infiltration to layer amorphous carbon on multi-walled nanotubes to improve structural integrity and achieve superhydrophobic behavior with tunable geometry. These carbon-infiltrated carbon nanotube (CICNT) surfaces exhibit an increased number of contact points between neighboring tubes, resulting in a composite structure with improved mechanical stability. Additionally, the native surface can be rendered superhydrophobic with a vacuum pyrolysis treatment, with contact angles as high as 160° and contact angle hysteresis on the order of 1°. The CICNT diameter, static contact angle, sliding angle, and contact angle hysteresis were examined for varying levels of carbon-infiltration to determine the effect of infiltration on superhydrophobicity. The same superhydrophobic behavior and tunable geometry were also observed with CICNTs grown directly on stainless steel without an additional catalyst layer. The ability to tune the geometry while maintaining superhydrophobic behavior offers significant potential in condensation heat transfer, anti-icing, microfluidics, anti-microbial surfaces, and other bio-applications where control over the nanostructure is beneficial. [ABSTRACT FROM AUTHOR]

Concentrated solar power (CSP), or solar thermal power, is an ideal technology to hybridize with other energy technologies for power generation. CSP shares technology with conventional power generation and can be readily integrated with other energy types into a synergistic system, which has many potential benefits including increased dispatchability and reliability, improved efficiency, reduced capital costs through equipment sharing, and the opportunity for flexible operation by alternating between energy sources, which can lead to improved overall efficiency through synergy of the different energy sources. Another advantage of CSP technology is the ability to readily store via thermal energy storage (TES), making the intermittent solar resource dispatchable. A review of CSP hybridization strategies with coal, natural gas, biofuels, geothermal, photovoltaic (PV), and wind is given. An overview of different configurations for hybridizing CSP with these other energy sources is also provided. Hybridized CSP plants present different types and levels of synergy, depending on the hybrid energy source, the location of the plant, the CSP technology used, and the plant configuration. Coal, natural gas, and biofuel hybrids with CSP present many opportunities to inject solar heat at various temperatures. These combustible fuels provide reliability, dispatchability, and flexibility but are not entirely renewable solutions (with the exception of biofuels). Geothermal, wind, and PV hybrid designs with CSP can be entirely renewable, but lack some of the benefits of hydrocarbon fuels. Effective geothermal-CSP hybrid designs require low temperature operation where efficiency is limited by the power cycle. Wind-CSP and PVT (photovoltaic/thermal) lack dispatchability, but have other advantages. The pursuit of ideal CSP hybrid systems is an important research topic as it allows for further development of CSP technologies while providing an immediate solution that increases the use of solar power. [ABSTRACT FROM AUTHOR]

Miniaturization of gas chromatography (GC) instrumentation is of interest because it addresses current and future issues relating to compactness, portability and field application. While incremental advancements continue to be reported in GC with columns fabricated in microchips (referred to in this paper as “microchip columns”), the current performance is far from acceptable. This lower performance compared to conventional GC is due to factors such as pooling of the stationary phase in corners of non-cylindrical channels, adsorption of sensitive compounds on incompletely deactivated surfaces, shorter column lengths and less than optimum interfacing to injector and detector. In this work, a GC system utilizing microchip columns was developed that solves the latter challenge, i.e., microchip interfacing to injector and detector. A microchip compression clamp was constructed to heat the microchip (i.e., primary heater), and seal the injector and detector fused silica interface tubing to the inlet and outlet ports of the microchip channels with minimum extra-column dead volume. This clamp allowed occasional operation up to 375 °C and routine operation up to 300 °C. The compression clamp was constructed of a low expansion alloy, Kovar™, to minimize leaking due to thermal expansion mismatch at the interface during repeated thermal cycling, and it was tested over several months for more than one hundred injections without forming leaks. A 5.9 m long microcolumn with rectangular cross section of 158 μm × 80 μm, which approximately matches a 100 μm i.d. cylindrical fused silica column, was fabricated in a silicon wafer using deep reactive ion etching (DRIE) and high temperature fusion bonding; finally, the channel was coated statically with a 1% vinyl, 5% phenyl, 94% methylpolysiloxane stationary phase. High temperature separations of C10-C40 n -alkanes and a commercial diesel sample were demonstrated using the system under both temperature programmed GC (TPGC) and thermal gradient GC (TGGC) conditions. TGGC analysis of a complex essential oil sample was also demonstrated. Addition of a secondary heater and polyimide insulation proved to be helpful in achieving the desired elution temperature without having to raise the primary heater temperature above 300 °C for high boiling point compounds. [ABSTRACT FROM AUTHOR]

Superhydrophobic surfaces have been shown to reduce drag in single-phase channel flow; however, little work has been done to characterize their drag-reducing ability found in two-phase flows. Adiabatic, air-water mixtures were used to explore the influence of hydrophobicity on two-phase flows and the hydrodynamics which might be present in flow condensation environments. Pressure drop measurements in a rectangular channel with one superhydrophobic wall (cross-section approximately 0.37 × 10 mm) and three transparent hydrophilic walls were obtained. Data for air/water mixtures with superficial Reynolds numbers ranging from 22–215 and 55–220, respectively, were obtained for superhydrophobic surfaces with three different cavity fractions. Agreement between experimentally obtained two-phase pressure drop data and correlations in the literature for conventional smooth control surfaces was better than 20 percent, which is within the accuracy of the correlations. The data reveal a reduction in the pressure drop for two-phase flow in a channel with a single superhydrophobic wall compared to a control scenario. The observed reduction is approximately 10 percent greater than the reduction that is observed for single-phase flow (relative to a classical channel). [ABSTRACT FROM AUTHOR]

High-aspect-ratio, porous membrane of vertically-aligned carbon nanotubes (CNTs) were developed through a templated microfabrication approach for electrochemical sensing. Nanostructured platinum (Pt) catalyst was deposited onto the CNTs with a facile, electroless deposition method, resulting in a Pt-nanowire-coated, CNT sensor (PN-CNT). Convective mass transfer enhancement was shown to improve PN-CNT sensor performance in the non‐enzymatic, amperometric sensing of hydrogen peroxide (H 2 O 2 ). In particular, convective enhancement was achieved through the use of high surface area to fluid volume structures and concentration boundary layer confinement in a channel. Stir speed and sensor orientation especially influenced the measured current in stirred environments for sensors with through-channel diameters of 16 μm. Through-flow sensing produced drastically higher signals than stirred sensing with over 90% of the H 2 O 2 being oxidized as it passed through the PN-CNT sensor, even for low concentrations in the range of 50 nM to 500 μM. This effective utilization of the analyte in detection demonstrates the utility of exploiting convection in electrochemical sensing. For through‐flow at 100 μL s −1 , a sensitivity of 24,300 μA mM −1 cm −2 was achieved based on the frontal projected area (871 μA mM −1 cm −2 based on the nominal microchannel surface area), with a 0.03 μM limit of detection and a linear sensing range of 0.03–500 μM. [ABSTRACT FROM AUTHOR]

• The spectral, directional emissivity of V-groove or corrugated surfaces is studied. • The apparent surface emissivity increases with decreasing V-groove angle. • Less spectral variation and more blackbody like behavior occurs for smaller angles. • Azimuth dependence can be small despite the obvious corrugation. Spacecraft thermal control is entirely reliant upon radiative heat transfer with its surroundings for temperature regulation. Current methods are often static in nature and do not provide dynamic control of radiative heat transfer. As a result, modern spacecraft thermal control systems are typically 'cold-biased' with radiators that are larger than necessary for many operating conditions. Deploying a variable radiator as a thermal control technique in which the projected surface area can be adjusted to provide the appropriate heat loss for a given condition can reduce unnecessary heat rejection and reduce power requirements. However, the radiative behavior of the apparent surface representing the expanding/collapsing radiator changes in addition to the projected surface area size. This work experimentally quantifies the spectral, directional emissivity of an apparent surface comprised of a series of V-grooves (e.g. corrugated surface), as a function of angle and highlights its emission characteristics that trend toward black behavior. The experimental setup for quantifying this apparent radiative surface behavior is described and utilized to show the influence of surface geometry, direction and wavelength. Experiments on test samples were performed at 573 K. The experimental design is validated and demonstrated using fully oxidized, nearly diffuse, copper, corrugated test samples. The results presented in this work demonstrate, for the corrugated oxidized copper surfaces tested, that (1) higher emissivity values correspond to higher wavelengths in the spectral range of 2.5 to 15.4 µm (2) apparent emissivity values increase with decreasing V-groove angle resulting in less spectral variation in emissivity and greater blackbody like behavior, (3) azimuth dependence can be relatively small despite the obvious pattern associated with a corrugated surface, and (4) as the V-groove angle decreases, higher emissivity values are associated with θ → 0 ∘ and ϕ → 0 ∘. Results provide a foundation for future radiator design, improved spacecraft thermal control methods, and improved emissivity testing methods for patterned or angular surfaces. [ABSTRACT FROM AUTHOR]

This work presents a process to determine the preliminary optimal configuration of a concentrating solar power-coal hybrid power plant with low solar augmentation, and is demonstrated on a regenerative steam Rankine cycle coal power plant in Castle Dale, UT, USA (average DNI of 542 W m − 2). A representative plant model is developed and validated against published data for a coal power plant. The simplifications that lead to the representative model from a coal power plant model include combining multiple feedwater heaters, combining turbines, and using a mass-average calculation for extraction steam properties. Comparing net power generation and boiler heating estimates from the representative model to the benchmark power plant, the representative model predictions are accurate to within ± 2.5% of the accepted value. Methods for quantifying solar resource based on geography and simulating a concentrating solar power field arrangement are provided and the solar contribution to electrical power output is estimated using an exergy balance. A financial model is also included to estimate the solar marginal levelized cost of electricity and payback time using a cash-flow analysis. A multi-objective optimization routine is then employed to determine the optimal configuration using the models described in this study. It is shown that a solar augmentation of > 3% of boiler heating is required for a hybrid design to be considered thermodynamically feasible. However, as the augment fraction is increased, the financial benefit from fuel savings is insufficient, without a carbon tax, to offset the higher capital cost. Optimization results, constrained to a maximum solar field size of 20 ac, are also provided assuming a common carbon tax value (16 USD sh.tn. − 1). The resulting optimal design for the Castle Dale Plant with a carbon tax and no premium indicates the use of parabolic trough collector technology at an augment fraction of k = 9 % to bypass feedwater heater 6. The resulting marginal solar levelized cost of electricity is 9.5 x 10 -4 USD kWh − 1 with an estimated payback time of 25.2 years. With a green energy premium price of 0.018 USD kWh − 1 and no carbon tax, the payback time reduces to 3.9 years. This process can be applied to a subcritical Rankine cycle coal power plant for which operating data and meteorological data are available to evaluate preliminary hybridization feasibility. • Method to determine an optimal hybridized solar-coal power plant is presented. • A representative model for different coal plant configurations is presented and validated. • Multi-objective optimization incorporates solar resource, LCOE, solar collection, and plant model. • Results indicate a green energy premium or carbon tax is required for reasonable payback time. [ABSTRACT FROM AUTHOR]

An abstract of the article "Infrared Visualization of the Cavity Effect Using Origami-Inspired Surfaces" by Mitchell J. Blanc and colleagues is presented.