Lyotropic liquid crystalline nanostructures formed by self-assembly in an aqueous medium are of fundamental interest and crucial for therapeutic applications, encapsulation of nutraceuticals, tissue engineering, and diagnostics. The biomimetic lipid bilayer building blocks impart biodegradable properties and low toxicity of the created nanoassemblies. The question of synergistic or quenching effects on the resulting bioactivity arises from the coencapsulation of multiple antioxidants (e.g., vitamin E (VitE), curcumin (CU), or coenzyme Q10) in nanocarriers of mixed nonlamellar-phase lipids (e.g., amphiphilic monoglycerides or plasmalogens with long polyunsaturated fatty acid (PUFA) chains). The response to this question should favor phytochemical-based therapies against oxidative stress and inflammatory disorders using sustainable nanomedicines. Herein, we investigate the nanodispersion of multicomponent antioxidant/lipid mixtures using the copolymer Pluronic F127 and three PEGylated amphiphiles (TPGS-PEG1000, MO-PEG2000, and DSPE-PEG2000). The purpose is to establish possible relationships between the amphiphilic pharmaceutical compositions, structural stability, degradability in the biological cell culture medium, and the effects on antioxidant activity. The structures and the topologies of the phytochemical-loaded mesophases were revealed by synchrotron small-angle X-ray scattering and cryogenic transmission electron microscopy imaging. We found that encapsulated antioxidants (CU, Q10, or VitE) fine-tune the lipid bilayer properties and the nanostructure of the self-assembled systems to form lamellar (L), inverted hexagonal (HII), or cubic (Im3m) liquid crystalline phases. The results demonstrated that the composition of the nanoassemblies (lipids, dispersing agents, and antioxidants) governs the structural organization through changes in the interfacial curvature and miscibility effects. A minimal toxicity of the nanoassemblies was observed in vitro using the human neuroblastoma cell line (SH-SY5Y). The biodegradability/stability of the nanodispersions was linked with gradual dynamic changes in nanoparticle size distribution in the biological cell culture medium (DMEM). The established enhanced reactive oxygen species (ROS)-scavenging activity of the liquid crystalline nanoformulations is of interest for developing safe pharmaceutical nanosystems for multitargeted delivery of poorly soluble phytochemicals.
Marianna Di Pietrantonio, Giacomo Russo, E. Guerra
et al.
State-of-the-art systems used to supply superconducting magnets in nuclear fusion devices introduce significant energy losses and impact the power quality of the external electrical grid. Additionally, current leads that transition from room to cryogenic temperatures represent a major source of heat load for the cryogenic system. While these are notable drawbacks in current experiments, they could become critical obstacles for the feasibility and costeffectiveness of future fusion reactors. Flux pumps are contactless, compact systems capable of inducing currents in superconductors with minimal operational losses. Several smallscale experiments have already demonstrated the feasibility of this concept, but no engineering designs or prototypes have yet been developed specifically for fusion magnets. As part of a research initiative focused on designing various types of flux pumps tailored to fusion applications, this paper outlines the general advantages of this approach, particularly in terms of energy consumption, but also in terms of compactness, modularity, and reliability. The numerical analysis presented focuses on the design of a flux pump intended to supply the DTT toroidal field coils. However, the developed model and insights are broadly applicable to a wide range of scenarios.
The intermetallic transition metal B2‐structured aluminide RuAl is a candidate material for use in various applications, including microelectronics and structural materials under demanding conditions, for example, as oxidation‐ and corrosion‐resistant materials. In contrast to other B2 transition metal aluminides, which usually suffer from brittle material behavior at room temperature, RuAl exhibits comparatively good room‐temperature ductility, in combination with further promising properties. Therefore, RuAl thin films are attracting interest as potential protective and functional surface engineering materials. The synthesis of RuAl thin films by physical vapor deposition, especially magnetron sputtering, is however complex and utilizes codeposition and multilayer from elemental sputtering targets and subsequent annealing procedures. Herein, an alternative route toward single‐phase B2‐structured RuAl thin films by nonreactive DC magnetron sputter deposition at low substrate temperature from a powdermetallurgically manufactured Ru50Al50 compound target is described. The influence of the deposition parameters on the constitution, microstructure, and selected properties of RuAl thin films is studied. It is shown that especially the Ar process gas pressure has a significant impact on their composition and morphology. X‐ray diffraction and transmission electron microscopy with selected‐area electron diffraction indicate that the films are single‐phase RuAl with B2 structure.
When temperature exceed 36 degrees with a large area and linger for minimum three or more days can be considered as heat wave (HW). In the Pre-monsoon, the sun ray drops down on the ‘Thar’ desert (India) and the foothill of the Himalayas vertically, the area makes a hot-tempered zone. That is why, these regions produce a trough of low and there is a possibility to advect temperature towards Bangladesh. The south/south westerly wind carries a high amount of moisture over Bangladesh. The heat capacity of moisture is higher than that of dry air. Solar insulation, temperature advection and moisture incursion are three main phenomena that are responsible for HW condition. Veering is also responsible for especially severe and very severe HW conditions. The present study is accompanying with all category’s frequency of heat wave days (HWD) and HW for the Pre-monsoon (March to May) over most of the stations (34) of Bangladesh for the period 1990-2019. Microsoft excel, Surfer and Arc GIS software have been used for data calculation, however, linear trend analysis and Mann-Kendall test have been used to draw the trend of HW frequency. The highest numbers of HWD are found in Jashore (30.9 days) of all types of events whereas the highest frequencies of HW are found in Rajshahi (4.2333) during pre-monsoon season. The lowest numbers of frequency of HWD and HW, both are found at Chattogram. April is the hottest month in Bangladesh. On the basis of frequency of HWD, the obtained highest hot places are Jashore, Chuadanga, Rajshahi, Ishurdi and Satkhira. while in Kutubdia and Teknaf, no HW is found at all. Among 30 years, 2014 is found the hottest year and 2018 is the recorded lowest hot year. By Mann-Kendall test, the HW trend of M. Court, Mongla, Patuakhali and Chandpur have indicated positive significant value, and Mymensing station has given only negative significant value. From spatial distribution, it shows the hottest areas which are south western and middle-western parts of Bangladesh. Journal of Engineering Science 14(2), 2023, 59-67
Processes involving droplet impact and subsequent freezing occur widely in practical engineering applications. In the present study, a visualization experimental setup is utilized to investigate the effects of the impact of single millimeter-scale droplets on curved surfaces at room and low temperatures. The influences of the Weber number We, wall temperature, and wall wettability on the dynamics of droplet impact and the characteristics of ice formation are examined. The morphological evolution of droplet impact and the variations of the dimensionless spreading coefficient are analyzed. The results indicate that at high We (We = 277), droplets reach their maximum spread on cold walls in a shorter time than on room-temperature walls, and their peak spreading coefficient is smaller. Upon impact with a cold wall, droplets exhibit a spread–splatter behavior. Low temperatures suppress the oscillatory behavior of droplets on a curved wall. In the case of a hydrophilic wall surface, as the impact We increases from 42 to 277, the impact mode gradually transitions from spread–retract–freeze to spread–splatter–freeze. The maximum spreading coefficient first increases and then decreases with increasing impact We. At high We (We = 277), the wall wettability has a minimal effect on the dynamics of droplet impact and freezing, with a spread–splatter–freeze mode being exhibited for both hydrophobic and hydrophilic walls, and the final freezing morphology is similar.
To address new challenges in the design of current and future advanced cryostats, guidelines can be developed by leveraging successful technical experience with existing cryostat assemblies. A brief review of eleven representative advanced cryostat designs is presented, based on six typical cooling methods, including cryogen baths, dry cryostats, mixed-cooling method, continuous cryogen flow, dilution refrigeration, and demagnetization. Also provided are engineering figures, tables-plots, and equations that can be used to design, configure, and optimize the thermal performance of cryostats. The following technical data are introduced: optimal Carnot power versus temperature for various two heat intercept stations in cryostat support, ten representative performances of different MLI blankets at various (Th-Tc), and a graphical summary of the ‘MLI patch-cover-crack’ experiments, among others. The cold mass thermally isolated in cryostats could be a quantum apparatus, test specimen, instruments in-space, or superconducting (SC) devices. The cryostat must provide all functional interfaces for obtaining the required data. The design methodologies for crucial components of a cryostat are discussed in-depth, including: 1) creating a lightweight support structure and placing thermal anchors in optimal locations, 2) designing MLI systems with cost-effective thermal shields, and 3) constructing sophisticated structures to accommodate heavy RF couplers or current leads.
Intermetallic γ‐TiAl based alloys are innovative structural materials dedicated to applications in the automotive and aeronautic industries. Especially their low density, high specific yield strength, and excellent resistance against creep and oxidation make them a suitable choice for structural high‐temperature components in combustion engines. However, further improvement of their properties and processability is required to conquer new application areas and facilitate cost‐effective production. While the incorporation of additional alloying elements is a promising possibility, their effects on the phase transformations and phase equilibria need to be considered rigorously. In this context, this review provides a detailed survey of the research work on the influence of technically important alloying elements on the Ti–Al phase diagram. First, an introduction to the fundamentals of the phase transformations in γ‐TiAl based alloys and the consequences of changed cooling conditions, relevant for example to the latest developments within the field of processing, is given. Afterward, the alloying elements, categorized with respect to their stabilization effect, are discussed and their particularities are highlighted. Topics covered include established ternary phase diagrams and isoplethal sections, the stabilization of additional phases as well as the influence of alloying elements on the microstructure of modern engineering intermetallic γ‐TiAl based alloys.
Abstract The thermo-hydraulic and exergy characteristics of a new design called a triple tube helical coil with an inner triangular twisted tube, TTHCITTT, were explored experimentally. The structure of the new design involved a modified inner twisted fluid path for the inner tube of a triple tube helical coil with an inner triangular twisted tube. The study involved the impact of various designing parameters such as twisted pitch ratio, coil torsion, coil inclination angle, Dean number, and double tube helical coil with an inner triangular twisted tube, as a particular reference. The experimental runs were carried out at a wide range of inner annulus Reynolds numbers from 3000 to 26,900 corresponding to velocities of 0.05 to 2.05 m s−1. The main remarks show that the triple tube helical coil with an inner triangular twisted tube presents superior thermo-hydraulic and exergetic characteristics compared to the double tube helical coil with an inner triangular twisted tube by 73.68%. While the twisted pitch ratio increased from ∞ (smooth) to 4.69, the Nusselt number was enhanced by 24.7% at the expense of increasing the friction factor by 36.4%. The coil torsion presents a noticeable impact on increasing the Nusselt number by 18.8% while the increase in f h is approximately 12%. The coil inclination angles of 0° and 90° present a higher Nusselt number compared to that of 45° by 9.3%. The maximum thermal performance factor reached 2.12 for a twisted pitch ratio of 4.69 and coil torsion of 0.068 and at a coil inclination angle of 90°. The smooth tube predicts a higher exergy destruction rate and dimensionless exergy loss than the corrugated tube by 25% and 26.9%, respectively. New correlations to predict the Nusselt number and the friction factor were correlated. Graphical Abstract
Low temperature engineering. Cryogenic engineering. Refrigeration
Çiğdem Bilici, Mine Altunbek, Ferdows Afghah
et al.
Cryogel-based scaffolds have attracted great attention in tissue engineering due to their interconnected macroporous structures. However, three-dimensional (3D) printing of cryogels with a high degree of precision and complexity is a challenge, since the synthesis of cryogels occurs under cryogenic conditions. In this study, we demonstrated the fabrication of cryogel-based scaffolds for the first time by using an embedded printing technique. A photo-cross-linkable gelatin methacryloyl (GelMA)-based ink composition, including alginate and photoinitiator, was printed into a nanoclay-based support bath. The layer-by-layer extruded ink was held in complex and overhanging structures with the help of pre-cross-linking of alginate with Ca2+ present in the support bath. The printed 3D structures in the support bath were frozen, and then GelMA was cross-linked at a subzero temperature under UV light. The printed and cross-linked structures were successfully recovered from the support bath with an integrated shape complexity. SEM images showed the formation of a 3D printed scaffold where porous GelMA cryogel was integrated between the cross-linked alginate hydrogels. In addition, they showed excellent shape recovery under uniaxial compression cycles of up to 80% strain. In vitro studies showed that the human fibroblast cells attached to the 3D printed scaffold and displayed spread morphology with a high proliferation rate. The results revealed that the embedded 3D printing technique enables the fabrication of cytocompatible cryogel based scaffolds with desired morphology and mechanical behavior using photo-cross-linkable bioink composition. The properties of the cryogels can be modified by varying the GelMA concentration, whereby various shapes of scaffolds can be fabricated to meet the specific requirements of tissue engineering applications.
The performance of a dual evaporator cycle using ejector is compared with a conventional cycle employing pressure reducing valve. In both the systems, high temperature evaporator is considered as a flooded evaporator, thus a separator is employed after the high temperature evaporator. However, low temperature evaporator is a kind of conventional dry evaporator. The comparison of both systems, i.e., conventional and ejector assisted, is done for the same cooling capacities and same dryness fraction at the exit of high temperature evaporator with R134a, R152a, and R1234yf refrigerants. The effects of varying the states of refrigerant at the exit of flooded evaporator, and temperatures of both the evaporators and the condenser are analyzed using Engineering Equation Solver. It is found that the compressor work is reduced in both the cycles with the rise in low temperature evaporator temperature; however, a little variation is observed in the total cooling effect. The cooling effect in high temperature evaporator is increased with the increase in dryness fraction at the exit of the high temperature flooded evaporator, but it is decreased in low temperature evaporator.
Increases in speeds and traffic density in railway sector impose challenges on the modern disk-pad brake systems such as higher temperatures and stresses resulting in hot-spots and a degraded system performance. The prediction of disk thermal behavior under challenging conditions has become an important engineering issue. In this study, a model is developed using the finite difference method (FDM) with realistic time-dependent boundary conditions and experimental convection correlations with non-uniform time-step size features. A previous numerical/experimental study on the thermal behavior of railway disc brake is partly adopted and enhanced. The results of the developed model agree well with the results of the previous study. A practical prediction method for thermal stresses in the disk is applied using the axial temperature distributions at several time instants from locations with highest temperature. Furthermore, same configuration of the disc with the pad is modelled in Simcenter STAR-CCM+ which is a validated commercial CFD software to compare the results and computation times with that of the developed model. Using this model, an investigation has been conducted on the effect of temperature-dependent material properties on thermal behavior. The developed numerical model can simulate the conditions experienced by a railway disk in a relatively new standard considering the transient thermal behavior and axial thermal stress distribution with relatively low computational time and reasonable accuracy. Also, valuable insights are obtained on the effect of variable thermal properties of the disk and convection correlations on the disk thermal behavior.
Engineering plastics are a group of plastics that are commonly used in industry because of their low density and enhanced mechanical and thermal properties. They can replace metals in many advanced fields, such as aerospace, aircraft and automobiles. With the introduction of cellular structure, engineering plastic foams present a further reduction of density as well as adding the properties of thermal insulation, sound insulation and mechanical damping. The traditional foaming methods for engineering plastics mainly use chemical foaming agents or combustible physical agents. Due to the high temperature resistance of engineering plastics, the chemical foaming method requires an inorganic foaming agent with a high decomposition temperature. Lower decomposition of the inorganic foaming agent results in a high foam density, for example, a 10–30% mass reduction. Physical foaming agents such as pentane, butane and acetone are also used in the extrusion foaming of PC, PET and PEI. Unfortunately, these physical foaming agents are flammable and exhibit poor cell nucleation ability, resulting in a cell size as large as 200–300 μm or even larger. In recent years, the microcellular foaming technology using supercritical CO2 or N2 fluids has received much attention from both academy and industry. CO2 and N2 are inert gases, which are environmentally more friendly, inexpensive and easy to obtain compared to the flammable agents, and can achieve supercritical state under mild conditions. Supercritical fluids have high solubility and high gas diffusivity in engineering plastic matrices, which is beneficial for inducing a large number of cell nuclei through a pressure quenching or temperature rising process. Therefore, the supercritical fluid physical foaming technology can induce a microcellular structure or even a nanocellular structure in engineering plastic foams, which endows the foams with excellent mechanical, thermal insulation and dielectric properties. This gives engineering plastic foams prospects for important applications in structural, acoustic, thermal insulation, flame-retardant and dielectric fields. For this special section, 17 articles from experts in the field of polymer foaming who focus on various engineering material systems such as ABS, UHMWPE, PEI, PEEK, PEN, etc., and various foaming technologies, such as extrusion foaming, injection foaming and autoclave foaming, to prepare engineering plastic foams with adjustable cell structures have been included. This special section also reports some novel polymer physical foaming technologies, such as micro-extrusion foaming of PEEK fiber and in-situ foaming and 3D printing of biomimetic porous PEI structure. In addition to the preparation of various engineering plastic foams, this section also focuses on the mechanical and functional properties of the foams.
The present paper investigated the relationship between low temperature impact toughness and microstructure of bainite in coarse-grained heat affected zone (CGHAZ) and intercritically rehazed CGHAZ (ICCGHAZ) of an offshore engineering steel from both the microstructure morphological and crystallographic aspects. In this work, six groups of samples simulated CGHAZ and ICCGHAZ were designated at three different cooling rates. The Charpy test results showed that the toughness in CGHAZ decreases dramatically with decrease of cooling rate, which was attributed to the microstructural evolution from lath bainite to granular bainite, accompanying with the size increase of Bain zone and the change of M/A morphology from film to block. The increase in hardenability by cooling rate promotes more crystallographic variants from different Bain groups. Meanwhile, the combination with controlled inter-spacing of block boundaries by self-accommodation below the critical Griffith crack length, micro-crack can be arrested by these high angle grain boundaries thereby suppressed brittle fracture initiation and increased fracture properties. However, the variation in toughness of ICCGHAZ is not a concern, since obtaining excellent toughness is scarcely accessible even if the matrix microstructure is analogous to CGHAZ. It was due to the formation of coarse M/A constituents (~2 μm) necklacing at the prior austenite grain boundary. The visualized crystallography suggested that the impact toughness was partially correlated to the configuration manner and the size of Bain zones as well via promoting highly misoriented angle (>45°) boundaries, which in turn effectively deflected or arrested the brittle crack propagation.