Local Thermal Gradient Research Articles

Matching and performance analysis of a solid oxide fuel cell turbine-less hybrid electric propulsion system on aircraft

Advanced low-carbon propulsion technology is one of the major initiatives to address aviation environmental challenges. In this paper, a solid oxide fuel cell turbine-less hybrid electric propulsion system is developed. It is a new engine, in which the power consumed by the compressor comes from a fuel cell, not a turbine. The aircraft's propulsion comes from the high-velocity exhaust discharged from the nozzles. To make the key fuel cell work properly and determine the system operating parameters, it is necessary to study the matching and performance of the hybrid electric propulsion system. In this study, a performance analysis model of the hybrid electric propulsion system is established. In particular, a one-dimensional fuel cell is simulated to obtain its localized thermal gradient. The results show that the hybrid electric propulsion system has a satisfactory performance under the design conditions. It is superior to the gas turbine-based engine in performance, and they have different performance trends. The operating range of compressor pressure ratio is determined. The sensitivity analysis shows that in addition to compressor pressure ratio, Mach number, reforming temperature, and fuel utilization have a great influence on the performance, which is worthy of further study.

Temporal and spatial effects of large airport construction and operation on the local thermal environment.

New construction has resulted in impervious surfaces increasingly replacing natural landscapes, altering surface radiation, thermal properties, and humidity in urban areas. Based on Landsat-8 data, the temporal and spatial impacts of the construction of Dalian Jinzhouwan Airport and Beijing Daxing Airport on the thermal environment were studied. The local thermal gradient (LTG) of the airport before and after construction is compared. The results showed that after the completion of the airport, the LTG value of Daxing Airport increased by 0.033 and that of Jinzhou Bay Airport increased by 0.009. After the airport operation, LTG values increase again. Daxing Airport added another 0.053, and Jinzhou Bay Airport added another 0.127. Two land classification models (land use type, LUT; local climate zone, LCZ) were used to explore the relationship between land use type and LTG. The results show that the increase of alloy buildings after the completion of the airport has a great influence on the thermal environment of the two study areas. The operation of airports will further enhance this effect. Our study can provide a reference for the influence of large-scale traffic construction on the urban thermal environment.

Dual-responsive nanomotors for deep tumor penetration and subcellular arrangement

The tumor tissue delivery of nanomaterials and the components’ intracellular location are particularly critical for the effect of tumor treatment. However, the abominable conditions in the tumor microenvironment hinder nanomaterials’ penetration, inducing the therapeutic action only on the surface of tumor tissue. And it is low-efficiency for therapy to spread nanomaterials in relatively expansive cytoplasm or organelles nonspecifically. Herein, we employed a near-infrared (NIR) light-induced self-propelled doxorubicin-loaded zeolitic imidazolate framework-8 capped copper sulfide Janus nanoparticles (CuS-ZIF-8-Dox JNPs) for deep tumor penetration and cancer therapy. The rocket-like Janus structure was rapidly synthesized by a dual-solvent method. Under NIR light irradiation, the rocket-like CuS-ZIF-8 JNPs showed directional wide-range motion. In addition, benefiting from the pH-responsive degradation of ZIF-8, various components were conveyed to the appropriate locations after cell internalization, i.e., Dox targeted the nucleus, and CuS nanoparticles escaped from lysosomes to the cytoplasm. Taking advantage of the local thermal gradient under the NIR light irradiation and intracellular arrangement for different components, this Janus nanocomposite displayed a deep tumor penetration, and achieved NIR and pH dual-responsive photothermal-enhanced chemodynamic therapy and chemotherapy in vitro and in vivo.

Geochemical exploration in Mesillas geothermal area, Mexico

This work presents results of geochemical exploration in the promising geothermal area of Mesillas, Nayarit, in the western border of the Mexican Volcanic Belt. The assessment of the geothermal resource was based on a geochemical approach which consisted in: (i) mapping and geological survey, (ii) chemical characterization of geothermal manifestations, (iii) diffuse flux analysis (CO2 and H2S), (iv) temperature at depth calculations using both classical and integrated multicomponent geothermometry.. Additional to the technical work, social dissemination of geochemical issues was attempted by designing and distributing a geomap among local people. The geological survey identified five andesitic units in an area of ∼1.5 km2, where 25 thermal springs discharge Na–CO3 water with temperatures between 47 and 90 °C, and pH ∼9. Geothermometric calculations indicate a bottom temperature between 125 °C and 130 °C. Andesites show high permeability generated by intense fracturing related with normal fault systems with trend NW-SE, SW-NE, NS, and EW. Surface hydrothermal alteration is mainly argillic with silicification. CO2 and H2S hydrothermal degassing are mainly restricted to thermal springs aligned in the NW-SE direction. Thermal springs with high temperature, highest degassing and high presence of hydrothermal alteration occur in the south-southwest zone of the geothermal area (MOL10, MOL13, MOL14 and MOL15); they correspond with NW-SE structural alignment. Furthermore, the estimated range of temperature at depth using geothermometers is 125–130 °C, and the surface temperature is on average 20 °C; considering local thermal gradient, it was estimated an equilibrium depth of 2.0–2.1 km. These results indicate that the Mesillas geothermal prospect may be classified as a medium temperature system with good permeability that may be exploited for electricity production as well as direct uses.

Crystallographic Variability in Additive Manufacturing

The crystallographic textures produced during additive manufacturing can be understood, predicted, and manipulated by varying the grain nucleation and growth processes. The resultant textures are primarily dictated by the melt pool geometry, which defines the local thermal gradient and thus the preferred crystal growth directions, as well as the scan strategy, which controls the propagation of grain orientations into subsequent layers. This texture can be diluted through heterogeneous nucleation of new grain orientations, which can occur through a variety of mechanisms. This ability to control the texture during additive manufacturing can enable the location-specific control of properties as a function of position in the build.

Spark plasma extrusion of binder free hydroxyapatite powder

Abstract This work explores the possibility of manufacturing dense and nanocrystalline hydroxyapatite (HA) large monoliths by spark plasma extrusion (SPE). This method combines uniaxial mechanical compression, high temperature, and electromagnetic field to promote the extrusion and sintering of HA powder in one single step. The results show that the binder-free extrusion of pre-compacted HA powder is feasible at a temperature similar to the temperature at which nanocrystalline HA shows superplastic behavior. The extrusion continues throughout the sliding and rotation of the particles, and also due to the grain boundary sliding, up to the point where no more material is available, thus producing monoliths of nearly 30 mm in length and 10 mm in diameter. The dehydration and smooth surface of the powder appear as paramount factors to facilitate the HA extrusion without additives. The extruded HA preserved the stoichiometry and nanometric grain size and exhibited preferential microstructural alignment in the direction of extrusion. The material experiences local thermal and pressure gradients during extrusion, producing different densification and hardness along its length. The SPE of HA will benefit the healthcare field by offering new processing approaches of bone substitutes and osteosynthesis devices.

Ferromagnetic domain wall manipulation using optically induced thermal gradients

Magnetic domain walls can be manipulated by thermal gradients. A local thermal gradient can be generated by illuminating the surface of a thin film sample with a focused femtosecond laser beam in relation to its intensity profile. We investigate the magnetic domain structures of a ferromagnetic [Co/Pt]3 multilayers under laser illumination. We create thermal gradients by either a stationary or a moving pulsed laser beam. Following the laser illumination, we use x-ray circular magnetic dichroism as a magnetic contrast mechanism in photoemission electron microscopy in order to image the magnetic domains. Our experimental results show that the domain walls drift towards the regions of higher temperature and align themselves parallel to the laser beam motion, leading to domains elongated in that direction.

Hierarchical Organization of Single Crystal Polymorphs of Azobenzene Chromophore in Anisotropic Media Subjected to Local Thermal Gradients upon Cold Spraying.

The present article entails the emergence of diverse crystal polymorphs following thermal quenching into various coexistence regions of binary azobenzene chromophore (ACh)/diacrylate (DA) solution and of azobenzene/nematic liquid crystal (E7) mixture. Development of various crystal topologies encompassing rhomboidal and hexagonal shapes can be witnessed in a manner dependent on thermal quenched depths into the crystal + liquid coexistence region of ACh/DA system. Upon spraying with compressed carbon dioxide (CO2 ) fluid, the local temperature gradient is generated resulting in spherulitic morphology showing discrete lamellae undergoing twisting locally in some regions and branched dendrites or seaweeds in another. When ACh/E7 blend is sprayed using compressed CO2 fluid, hierarchical organization of various discrete faceted single crystals including needle, rectangular, rhombus, and truncated hexagonal crystals radiating from the spherulite core can be discerned in a brighter region (off cross-polarization) polarized optical microscopy (POM) and nematic disclination in a darker cross-polarized region. Of particular interest is that the observed faceted single-crystal polymorphs in ACh/E7 may be contrasted to the lamellar twisting and branching observed in the ACh/DA system and plausible mechanisms of polymer spherulitic growth are discussed.

Texture evolution in a CrMnFeCoNi high-entropy alloy manufactured by laser powder bed fusion

Additive manufacturing (AM) techniques including laser powder bed fusion have been widely used to produce metallic components with microstructures and mechanical properties distinctly different from the conventionally manufactured counterparts. Understanding how AM parameters affect the evolution of microstructure, including texture, of these AM metallic components is critical for appropriate manipulation of their processing and therefore their mechanical properties. Here we conducted a systematic investigation of texture evolution of a face-centred cubic CrMnFeCoNi high-entropy alloy cuboid fabricated using laser powder bed fusion. Our results showed that the texture evolutions along the build direction were different between the corner and central parts of the sample. Detailed analysis suggested that the texture evolution is closely related to local thermal gradient, which is a property that can be manipulated through changing AM parameters. The different textures lead to the significant variations of mechanical properties within the sample.

Enzyme-Based Mesoporous Nanomotors with Near-Infrared Optical Brakes.

As one of the most important parameters of the nanomotors' motion, precise speed control of enzyme-based nanomotors is highly desirable in many bioapplications. However, owing to the stable physiological environment, it is still very difficult to in situ manipulate the motion of the enzyme-based nanomotors. Herein, inspired by the brakes on vehicles, the near-infrared (NIR) "optical brakes" are introduced in the glucose-driven enzyme-based mesoporous nanomotors to realize remote speed regulation for the first time. The novel nanomotors are rationally designed and fabricated based on the Janus mesoporous nanostructure, which consists of the SiO2@Au core@shell nanospheres and the enzymes-modified periodic mesoporous organosilicas (PMOs). The nanomotor can be driven by the biofuel of glucose under the catalysis of enzymes (glucose oxidase/catalase) on the PMO domain. Meanwhile, the Au nanoshell at the SiO2@Au domain enables the generation of the local thermal gradient under the NIR light irradiation, driving the nanomotor by thermophoresis. Taking advantage of the unique Janus nanostructure, the directions of the driving force induced by enzyme catalysis and the thermophoretic force induced by NIR photothermal effect are opposite. Therefore, with the NIR optical speed regulators, the glucose-driven nanomotors can achieve remote speed manipulation from 3.46 to 6.49 μm/s (9.9-18.5 body-length/s) at the fixed glucose concentration, even after covering with a biological tissue. As a proof of concept, the cellar uptake of the such mesoporous nanomotors can be remotely regulated (57.5-109 μg/mg), which offers great potential for designing smart active drug delivery systems based on the mesoporous frameworks of this novel nanomotor.

A spiral laser scanning routine for powder bed fusion inspired by natural predator-prey behaviour

ABSTRACT Additive manufacturing by laser powder bed fusion (LPBF) requires process parameters that consider both local and global thermal gradients to address material and component quality issues caused by non-uniform heating and cooling. Here, we develop an analogy between natural predator-prey behaviour and heat flow in LPBF, and consequently derive a spiral pattern that is translated into a discrete vector pattern compatible with LPBF. A power optimisation routine is applied to the spiral pattern to maintain constant melt pool depth, and the simulated thermal histories are compared to well-established zig-zag and helix scan patterns. From these results, we propose that the spiral pattern reduces the spatial variation of temperature, while a larger area remains above a specified threshold temperature at the end of the scan. Consequently, the spiral pattern may be promising for printing crack-prone materials, and for parameter optimisation of LPBF overall, and should be experimentally validated in future work.

Chemical design of self-propelled Janus droplets

Chemical design of self-propelled Janus droplets

Local-thermal-gradient and large-scale-circulation impacts on turbine-height wind speed forecasting over the Columbia River Basin

Abstract. We investigate the sensitivity of turbine-height wind speed forecast to initial condition (IC) uncertainties over the Columbia River Gorge (CRG) and Columbia River Basin (CRB) for two typical weather phenomena, i.e., local-thermal-gradient-induced marine air intrusion and a cold frontal passage. Four types of turbine-height wind forecast anomalies and their associated IC uncertainties related to local thermal gradients and large-scale circulations are identified using the self-organizing map (SOM) technique. The four SOM types are categorized into two patterns, each accounting for half of the ensemble members. The first pattern corresponds to IC uncertainties that alter the wind forecast through a modulating weather system, which produces the strongest wind anomalies in the CRG and CRB. In the second pattern, the moderate uncertainties in local thermal gradient and large-scale circulation jointly contribute to wind forecast anomaly. We analyze the cross section of wind and temperature anomalies through the gorge to explore the evolution of vertical features of each SOM type. The turbine-height wind anomalies induced by large-scale IC uncertainties are more concentrated near the front. In contrast, turbine-height wind anomalies induced by the local IC thermal uncertainties are found above the surface thermal anomalies. Moreover, the wind forecast accuracy in the CRG and CRB is limited by IC uncertainties in a few specific regions, e.g., the 2 m temperature within the basin and large-scale circulation over the northeast Pacific around 140∘ W.

Microstructural characterisation of thick-walled wire arc additively manufactured stainless steel

• Microstructural features of a thick-walled WAAM stainless steel part are investigated. • Microstructure exhibits periodically repeating characteristics across the WAAM part. • Oriented and textured structure with large grains at the overlapping region of adjacent fusion zones. • Significant spatial variations in terms of fusion zone shape, grain structure, texture, and phases. Wire arc additive manufacturing (WAAM) is a class of technologies suitable for producing large parts due to its high material deposition and building rates. Among the many possible materials processed by WAAM, austenitic stainless steels, e.g. 316L, are commonly employed. The structure of WAAM 316L thin parts has been studied extensively before. However, multiwalled or thick WAAM 316L parts remain largely unexplored. Hence, in this study, the microstructure of a thick 316LSi WAAM part is characterised in detail. The microstructure of the part consists of large and highly-oriented columnar grains dominated by epitaxial and competitive growth. The overlapping regions between neighbouring fusion zones contain long grains with a dominant <100> texture, which cross several layers and are aligned with the building direction. The grains' internal microstructure consists of an austenite matrix, ferrite with locally varying dendritic morphologies and dispersed oxide inclusions. The texture spatially varies across the part, and this variation is correlated to the local thermal gradient induced by the building strategy and processing conditions used during the manufacturing of the thick-walled part.

Shining new light on the motion of eutectic droplets across surfaces: A PEEM study of PtGe on Ge(110)

Thermally stimulated motion of micron-sized eutectic PtGe droplets on Ge(110) has been studied in situ mainly by photoemission electron microscopy, low-energy electron microscopy, and spatially resolved low-energy electron diffraction. In line with earlier studies of eutectic AuSi, PtSi, AuGe, and PtGe clusters on, respectively, various Si and Ge substrates we find that the motion toward regions at higher temperature is driven by the entropy gain of substrate atoms which become constituents of the droplet during its journey. At \ensuremath{\sim}1100 K, i.e., well above the bulk eutectic temperature, the direction is governed solely by the local thermal gradient, irrespective of eventual crystalline preferences. Access to the diffusivity of the host material (in this case Ge) inside the eutectic droplets shows that this is well above one order of magnitude higher than expected if it was rate limiting for the velocity of the moving droplets. This excludes a significant gradient of the (Ge) concentration inside the droplet and disqualifies dissolution-diffusion-deposition flow as the driving force for motion of the droplets on the surface, as assumed widely hitherto, to explain surface diffusion of eutectic droplets on surfaces. In addition, the interface between the droplet and the surface appears flat and we find no indication for ``endotaxy.'' The droplets make direct contact with the flat Ge substrate through atomic steps, which are abundantly present at the interface. The droplets are surrounded by a $\mathrm{Pt}{\mathrm{Ge}}_{3}$ wetting layer with an ordered (2 \ifmmode\times\else\texttimes\fi{} 1) structure. Dissolution of the edges of the wetting layer at the leading edge of the droplet with an activation energy of 2.2 eV is identified as the rate limiting step for its motion.

A narrative loom of hybrid nanofluid-filled wavy walled tilted porous enclosure imposing a partially active magnetic field

Improved controllability along with enhanced thermal performance in modern thermal devices could be achieved using the combination of partial magnetic fields and hybrid nanofluid flow. The present attempt demonstrates the impact of partially active magnetic fields on the enhanced thermal performance of hybrid nanofluid (Cu–Al2O3–H2O) flow in an oblique wavy porous enclosure. The enclosure is partially heated from the bottom and cooled through its wavy sides and suffers from a partially active magnetic field normal to the sidewalls. The transport equations involving complex wavy walls, localized thermal gradient, porous substance, hybrid nanofluid, partial magnetic fields are solved by the finite volume approach numerically using a written FORTRAN code. The effectiveness of the novel implementation of a partial magnetic field is examined rigorously for wide ranges of variations of active heating length (Lh), active width of the partial magnetic field (Wb) and its positions, magnetic field strength (Ha), the inclination of the cavity (γ), Darcy-Rayleigh number (Ram), Darcy number (Da), and hybrid nanoparticles concentration (ζ) additionally applying no and whole-domain magnetic field. The correlation for the average Nusselt number is derived. Finally, the results conclude that the presence of complex wavy walls enhances the heat transfer of ∼22.16% compared to a plain vertical wall; however, the strength of circulation drops. A partially active magnetic field can be utilized as an effective means to control field variables with a lesser reduction in heat transfer (∼13.97%) compared to the whole domain magnetic field. The middle-centered partial magnetic field offers a significant impact on the overall thermal behavior depending on the active width and intensity of the magnetic field, active heating length, and all other involved parameters. Tilting of the cavity reduces the heat transfer rate.

Effects of melt convection on stray grain formation in single crystal superalloys during directed energy deposition

During laser repairing of Ni-based single crystal (SX) superalloys, stray grain (SGs) formation leads to a deterioration of high-temperature properties and hot cracking. The main goal is to prevent SGs formation from forming, which controls the local solidification front thermal gradient ( G ) and solidification velocity ( V ). Meanwhile, the melt pool geometry, which is influenced by melt convection, has a significant impact on G and V . Here, experiments and theoretical calculations were used to study the evolution of the melt pool geometry during melt convection and its effects on the formation of SGs. Melt convection, i.e., Marangoni convection, outperformed thermal conduction in the SX superalloys melt pool during directed energy deposition, as evidenced by the estimated Peclet number and Prandtl number. The integrative impact of laser power, scan velocity, and beam diameters exacerbated Marangoni convection as the laser energy density distribution increased. Marangoni convection caused the melt pool shape to change from a near-semicircle to an undulating morphology, promoting the oriented-to-misoriented crystal growth transition and resulting in high stray grain sensitivity. The heat and mass transport in front of the dendrite tips was altered by Marangoni convection, which aggravated the deviation of the epitaxial dendrite orientation with respect to the substrate. This work provides an in-depth insight into controlling SG formation during additive manufacturing of SX superalloys. • The melt pool geometry transformed from a near semicircle to an undulating morphology by Marangoni convection. • The interaction between the thermal conduction and thermal convection was calculated for SX superalloys. • The mechanism of the melt pool geometry evolution resulting from Marangoni convection was proposed. • Marangoni convection promoted the oriented-to-misoriented transition leading to high sensitivity of stray grains. • Marangoni convection aggravated the epitaxial growth deviation by altering the heat and mass transfer.

Thermo-economic analyses of solid oxide fuel cell-gas turbine hybrids considering thermal cell gradients

The thermodynamic performance of a solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid system has been investigated at steady state operating conditions considering overall cell temperature differences and local thermal gradients inside the SOFC. The obtained simulation results served as input for the thermo-economic evaluation of the SOFC-GT hybrid. The system has been studied at two different operating voltages, various operating pressures, and fuel utilization factors. The results show that operating the system at higher fuel utilization factors and higher pressure ratios results in a substantially increased air flow requirement to maintain acceptable temperature differences and thermal gradients. The highest efficiency is obtained at the higher operating voltage of the two studied scenarios, a moderate pressure ratio of 5 bar and a moderate fuel utilization of 87.6%. However, the lowest cost of electricity is obtained at the lower operating voltage, the same pressure ratio and a lower fuel utilization compared to the highest efficiency case. • Using only GT exhaust gas recuperation achieves highest efficiency. • Pressure ratios around 5 bar achieve highest efficiencies. • Pressure ratios around 5 bar achieve lowest cost of electricity. • Fuel utilization around 85% achieves lowest cost of electricity.

Acoustic Steering Using Thermally Induced Optical Reflection of Sound (THORS)

Using the recently discovered THermally induced Optical Reflection of Sound (THORS) phenomenon, it is possible to generate optically induced, local density barriers in air by the absorption of intense, modulated laser light (the THORS phenomenon), which results in abrupt differences in compressibility of the air at these barriers that can efficiently reflect incident acoustic waves. In this note, we demonstrate the ability to optically manipulate and reflect acoustic waves in air as well as optimize the functional parameters (optical modulation and acoustic frequency) and characterize the effects of common physical parameters, including localized thermal gradients and incident angle of reflection on the efficiency of the resulting acoustic reflection. Finally, the ability to efficiently steer acoustic waves around a physical obstruction using THORS is also demonstrated.

Dendritic Growth Transition During Laser Rapid Solidification of Nickel-Based Superalloy

The dendritic growth transition of nickel-based superalloy in the top region of the laser additive manufactured layer has been studied. The results show that the dendritic growth direction in the top region of the layer is changed from the perpendicular to parallel direction to the laser scanning direction. From the finite element simulation, the dendritic growth transition is found to be attributed to the increased deviation angle between the epitaxial dendritic growth direction and local thermal gradient in the top region of the molten pool. The critical transition angle is revealed to be 70°–80°. The origin of the top transition grains is mostly the re-nucleation sites generated in the last remaining liquid in the top region of the molten pool.