Abstract

In this study, a computational fluid dynamics (CFD) model is developed for a radio frequency (RF) plasma system designed for powder spheroidization. The electric field is generated analytically by solving the RF coil system, and then the resulting equations are implemented as user-defined functions (UDF) to the CFD model. UDF codes were created and defined in the Fluent program to generate RF plasma. Electromagnetic fields and fluid flow have been modelled in numerical analysis studies, and temperature and velocity distributions were obtained. The effect of this plasma environment on titanium particle temperature is investigated using various particle-feeding gas flow rates. As a result, it is observed that an optimal powder-feeding rate could be determined. It is seen that high particle velocities prevent the attainment of the necessary temperature for melting, while low velocities may cause the temperature to exceed the boiling point. These results conclude that the feeding gas flow rate could be determined for a specific powder size range to obtain the powder temperatures within the melting and boiling temperatures.

Abstract

The heat extraction from the conventional channels under two-phase flow boiling conditions with water as the coolant is investigated numerically in this work. The numerical investigation was carried out by using ANSYS Fluent 2022R1 commercial software by selecting the Rensselaer Polytechnic Institute (RPI) wall heat flux partitioning approach by employing the Eulerian-Eulerian two-phase model. A three-dimensional computational domain was used for the simulation to understand the fluid boiling inside the conventional channel under steady state conditions, focusing on the effect of aspect ratio (AR) on the vapor volume fraction. The simulations were performed for a constant mass flux of 150.46 kg/m²-s with the heat flux value ranging from 10-100 kW/m² and at the inlet subcooled temperatures of 303K, 313K and 323K. The temperature of the channel bottom surface and the heat transfer coefficient (HTC) obtained numerically were compared with the experimental results and it was found that the results matched well. The volume of vapor fraction increased with the increase in heat flux for all values of inlet subcooled temperature considered in this study for all the test sections. At low inlet subcooled temperature, the volume of vapor fraction decreased with an increase in AR at all heat fluxes. However, there was no observable trend at higher heat flux and high inlet subcooled temperature.

Abstract

Work is reported on thermal-induced redshifts of quantum particle plasmon. The redshifts are predicted to be caused indirectly by the quantum size effects. The particles are enlarged when temperature increases, and consequently, quantum size effects modify the plasmon but not the band structure. It has been modeled for metallic quantum particles. The results are also instructive to other quantum systems, such as complex molecules.  Every electron inside the quantum particle is taken into account. Tiny quantum size effects are harvested, and the redshift becomes significant. Experimental evidence is also given for the spectral redshift. Faujasite zeolites were synthesized. Optical spectroscopy has been carried out, and the resulting spectra showed a significant redshift with the increase in temperature.

Abstract

A new method has been proposed to estimate top heat losses of vertical flat plate liquid/air collectors with double glazing. Empirical relations have been developed for the temperatures of glass covers, thus facilitating the calculation of individual heat transfer coefficients.  The values of individual heat transfer coefficients therefore obtained can be used in the proposed analytical equation for the estimation of the top heat loss coefficient of the vertical collector with double glazing.  The analytical equation has been developed for collector tilt angle of 60 to 90 degrees, plate temperature of 323 K to 423 K, absorber coating emittance of 0.1 to 0.95, air gap spacing of 20 mm to 50mm between the plate and inner glass cover, air gap spacing of 20 mm to 50mm between glass covers, wind heat transfer coefficient of 5 W/m²K to 30 W/m²K, and ambient temperature of 263K to 313K. The accuracy of the analytical equation has been validated for the said range of variables in comparison to numerical solutions, and the values of the top heat loss coefficient are found to be within 2.5 percent compared to numerical solutions.  

Abstract The Method of Discretization in Time (MDT) is a hybrid numerical technique intended to alleviate upfront the computational procedure of timedependent partial differential equations of parabolic type upfront. The MDT engenders a sequence of adjoint second order ordinary differential equations, wherein the space coordinate is the independent variable and time becomes an embedded parameter. Essentially, the adjoint second order ordinary differential equations are considered of “quasistationary” nature. In this work, the MDT is used for the analysis of unsteady heat conduction in regular bodies (large wall, long cylinder and sphere) accounting for nearly constant thermophysical properties, uniform initial temperature and surface heat flux. In engineering applications, the surface heat flux is customarily provided by electrical heating, radiative heating and pool fire heating. It is demonstrated that the approximate, semianalytical temperature solutions of the first adjoint “quasistationary” heat conduction equations using the first time jump are easily obtainable for each regular body. For enhanced acccuracy, regression analysis is applied to the deviations of the dimensionless surface temperature as a function of the dimensionless time for each regular body.

Abstract

In response to the prevailing energy crisis, this research focuses on elevating the potential of lithium niobate (LN) thin films for advanced optoelectronic applications. Employing electron beam evaporation, films undergo precise annealing (700°C to 1100°C), revealing a structural evolution through X-ray diffraction—crystallite sizes transition from 69.34 nm (unannealed) to 47.90 nm (1100°C). Scanning electron microscopy captures the transformation from coarse grains to photonic crystal clusters, while energy dispersion X-ray analysis discloses LN's composition (97.27 wt.% oxygen, 2.73 wt.% niobium). Rutherford backscattering spectroscopy illustrates surface damage post-Helium ion implantation, proportionate to depth. UV-VIS spectrophotometry highlights a significant blue shift in the optical band gap (3.70 eV to 2.52 eV), with further reduction at 700°C (2.48 eV) and a climactic shift at 1100°C (2.68 eV). This study not only addresses the pressing energy crisis but also emphasizes the indispensable role of lithium niobate in shaping the future of optoelectronics. It provides insights into tailoring LN properties for sustainable advancements in optoelectronic devices, marking a crucial chapter in our collective journey towards energy resilience. The urgency of innovation in the face of global challenges is underscored, marking a crucial chapter in our collective journey towards energy resilience.

Abstract

This research investigates the effects of drying on some selected vegetables, which are Telfaria occidentalis, Amaranthu scruentus, Talinum triangulare, and Crussocephalum biafrae. These vegetables were collected fresh, sliced into smaller sizes of 0.5 cm, and dried in a convective dryer at varying temperatures of 60.0 ℃, 70.0 ℃ and 80.0 ℃ respectively, for a regulated fan speed of 1.50 ms⁻¹, 3.00 ms⁻¹ and 6.00 ms⁻¹, and for a drying period of 6 h. It was discovered that the drying rate for fresh samples was 4.560 gmin⁻¹ for Talinum triangulare, 4.390 gmin⁻¹ for Amaranthu scruentus, 4.580 gmin⁻¹ for Talinum triangulare, and 4.640 gmin⁻¹ for Crussocephalum biafrae at different controlled fan speeds and regulated temperatures when the mass of the vegetable samples at each drying time was compared to the mass of the final samples dried for 6 h. The samples are considered completely dried when the drying time reaches a certain point, as indicated by the drying rate and moisture contents tending to zero. According to drying kinetics, the rate of moisture loss was extremely high during the first two hours of drying and then steadily decreased during the remaining drying duration. The rate at which moisture was removed from the vegetable samples after the drying process at varying regulated temperatures was noted to be in this trend: 80.0 ℃ > 70.0 ℃ > 60.0 ℃ and 6.0 ms⁻¹ > 3.0 ms⁻¹ > 1.5 ms⁻¹ for regulated fan speed. It can be stated here that the moisture contents have significant effects on the drying rate of the samples of vegetables investigated because the drying rate decreases as the regulated temperatures increase and the moisture contents decrease. The present investigation is useful in the agricultural engineering and food engineering industries.

Abstract Based on the application of phase diagram calculation technique (CALPHAD), the Fe-Nd-B magnetic materials were investigated, and alloy design and microstructure evolution concerning. According to the thermodynamic database of Fe-Nd-B ternary system, the equilibrium solidification process of Fe78Nd15B7 alloy is simulated, and we explained well the reason of this experimental phenomenon by the metastable extension of the equilibrium phase diagram.

Abstract

The use of porous media to simplify the thermohydraulic of a nuclear reactor is the topic of recent research. As a case study, the rector of 200 kW installed at Missouri University of Science and Technology is modeled in this paper. To help this objective, a fundamental CFD examination was completed to supplement the neutronics investigation on the present reactor. Characteristics of thermal energy removal from a typical research reactor are modeled by numerical thermal transport in porous media. The neutron flux is modeled by the nodal expansion method. For the thermo-hydraulic part, a three-dimensional governing equation is solved by an iterative method to find the steady-state solution of fluid flow and temperature in loss of coolant condition where the heat produced in the reactor core is removed by free convection. The profiles of heat flux for various power levels are benchmarked. Pressure, temperature, and velocity contours in the power passage were assessed at 300 kW and 500 kW power levels. To reduce the computational cost, a porous media approach for the whole geometry was utilized. The numerical results agree with the experimental results. The developed model can be used for safety and reliability analysis for various loss of coolant accidents.

Abstract

A large number of publications devoted to a new class of materials - high-entropy alloys (HEA), is associated with their unique chemical, physical and mechanical properties both in cast materials and in various classes of coatings and refractory compounds.

As a result of the research, the features of solid-soluble high-entropy alloys based on BCC and FCC phases have been revealed. These include the role of the most refractory element in the formation of the lattice parameter, the relationship of distortion with elastic deformation, and the contribution of the enthalpy of mixing to the strength and modulus of elasticity.  This made it possible, on the basis of Hooke's law, to propose a formula for determining the hardness of the HEA based on the BCC and FCC phases.

Based on the fact that with an increase in temperature in high-entropy alloys, the values of the modulus of elasticity, distortion and enthalpy of mixing will obey the same laws, a formula is proposed for determining the yield strength depending on the test temperature of solid-soluble HEA based on BCC and FCC phases. A formula based on the role of the most fusible metal in the alloy is proposed to calculate the melting point of solid-soluble materials.  

Abstract

Access to clean drinking water is universally recognized as a fundamental human right, yet millions globally still lack safe water. Contaminants such as heavy metals, organic compounds, and microbial pathogens pose significant health risks. Traditional water purification methods, while effective, often come with high costs and may not remove all types of contaminants. There is a need for more accessible and comprehensive solutions to improve drinking water quality. This study aims to explore the efficacy of activated carbon as a viable solution for enhancing drinking water quality and to identify the mechanisms through which it purifies water. The research involved a review of existing literature on activated carbon, including its various forms (powdered, granular, black carbon filters) and sources (coal, coconut shells, wood, peat). The study analyzed the physical and chemical processes of adsorption and the factors influencing these mechanisms. Activated carbon significantly increases surface area and adsorption capacity, enabling effective removal of a diverse range of pollutants, including volatile organic compounds (VOCs), chlorine, heavy metals, and certain harmful microbes. The findings suggest that activated carbon is a promising and cost-effective alternative for improving drinking water quality, with potential applications in various contexts to enhance public health and access to safe water.

Abstract

Heat transfer enhancement (HTE) is a topic of everlasting importance in thermal engineering research. The latest focuses in this field are on nanosolutions for more efficient thermal transmission fluids (a) and designs of metallic foams (b) Metallic foams provide extended surfaces for HTE and possess advantages such as a high value of Cp, high thermal conductivity (TC) and being light weight. nanosolutions, on the other hand, can be used as an efficient HT medium as they exhibit higher TCs in comparison to base fluids. This review paper summarizes the physical properties of nanosolutions and or within the metal foam, focusing on HT and flow properties of nanosolutions, metal foam and combined NS-metal foam systems. The inspiration novelty for this review is the basic transference identifications for the HT enhancement of nanosolutions in porous media. The aim of the work is to provide insight on how nanosolutions in conjunction with porous media can be useful for HTE.

Abstract The two-phase flow in micro/mini channels is of fundamental importance for many interesting applications, such as cooling of micro-electronic components and devices by a compact heat exchanger, material processing and thin-film deposition technology, bioengineering, and biotechnology. This article discusses significant developments made in the past ten years by researchers in the fields of pool boiling and convective boiling, using water, nanofluids, and refrigerants as the working fluids. The literature's data is examined in terms of improvements and declines in the critical heat flow and nucleate boiling heat transfer.Conflicting data have been presented in the literature on the effect that nanofluids/refrigerants have on the boiling heat-transfer coefficient; however, almost all the researchers have noted an enhancement in the critical heat flux during nanofluid/refrigerant boiling. Several researchers have observed nanoparticle deposition at the heater surface, which they have related to the critical heat flux enhancement

Abstract

Heat transfer fluids (HTFs) are critical in numerous industrial processes, enabling efficient heat exchange and precise temperature control. HTF degradation, primarily from thermal cracking and oxidation, negatively impacts system performance, reducing fluid lifespan and increasing operational costs, thus necessitating regular monitoring and proactive management. This review assesses optimal sampling frequencies for organic and synthetic HTFs, considering degradation mechanisms, relevant analytical parameters, and the economic advantages of proactive monitoring. The objective of this review is to examine HTF degradation mechanisms, compare organic and synthetic fluid properties and their impact on sampling frequency, and discuss strategies for optimising system performance and extending fluid life through effective HTF condition management. The article highlights the importance of fluid management, including appropriate fluid selection, to optimise system and fluid health, which is crucial for maximising their lifespans, ensuring safe operation, and minimising costs.

Abstract Proposed herein is an environment-friendly method to realize oil/water separation. Nylon mesh is exposed to atmospheric pressure plasma for surface modification, by which micro/nano structures and oxygen-containing groups are created on nylon fibers. Consequently, the functionalized mesh possesses superhydrophilicity in air and thus superoleophobicity underwater. The water pre-wetted mesh is then used to separate oil/water mixtures with the separation efficiency above 97.5% for various oil/water mixtures. Results also demonstrate that the functionalized nylon mesh has excellent recyclability and durability in terms of oil/water separation. Additionally, polyurethane sponge slice and polyester fabric are also functionalized and employed to separate oil/water mixtures efficiently, demonstrating the wide suitability of this method. This simple, green and highly efficient method overcomes a nontrivial hurdle for environmentally-safe separation of oil/water mixtures, and offers insights into the design of advanced materials for practical oil/water separation.