Metal Heat Research Articles

Improved Method for Methane Pyrolysis Rate Measurement using Molten Metal Catalysts for Turquoise Hydrogen Production

Abstract To develop low-$$\hbox {CO}_2$$ CO 2 emission ferrous metallurgical process, $$\hbox {H}_2$$ H 2 -based ironmaking processes are being actively developed. Several technologies are being developed to provide a sufficient mass of $$\hbox {H}_2$$ H 2 in an environmentally friendly manner. One of such processes is “turquoise” $$\hbox {H}_2$$ H 2 , based on a natural gas pyrolysis such as $$\hbox {CH}_4$$ CH 4 (g) $$\rightarrow $$ → 2$$\hbox {H}_2$$ H 2 (g) + C(s), thereby minimizing $$\hbox {CO}_2$$ CO 2 emission. The reaction could be catalyzed using molten metals in a bubble column reactor. Therefore, the selection of the molten metal catalyst is important for enhancing the reaction efficiency and for minimizing the production cost. In the previous research of the present authors, a new methodology for the pyrolysis rate measurement was introduced by employing an electromagnetic levitation heating of catalytic molten metals followed by quadrupole mass spectrometer (QMS) analysis to assist in the selection of the catalyst metal. However, a potential source of error in this technique was identified. Therefore, two modifications of the methodology are reported in the present study: (1) changing the heating and feed gas supply patterns and (2) gas analysis technique from QMS to Gas Chromatography (GC). Accordingly, the reported pyrolysis rate of pure In, Ga, Bi, Sn, and Cu of the previous study was revised in the present study. It was revealed that Ga and In emitted non-negligible amounts of $$\hbox {H}_2$$ H 2 upon heating, even without the fuel gas ($$\hbox {CH}_4$$ CH 4 ). This was regarded as a noise in the $$\hbox {H}_2$$ H 2 signal measured by GC. On the other hand, Cu, Sn, and Bi did not show the noticeable $$\hbox {H}_2$$ H 2 (noise). The modified method provides $$\hbox {H}_2$$ H 2 production rate by the pyrolysis, by separating the noise in the regime of the chemical reaction control at the surface of the molten metals. $$1^\text {st}$$ 1 st -order reaction was confirmed. Graphical Abstract

Low cross talk, low P π silicon optical switch based on highly balanced couplers and folded phase shifters

The cross talk and power consumption of the 2 × 2 optical switch is a key metric in the design of large-scale photonic integrated circuits (PICs). We build a theoretical model of a 2 × 2 Mach–Zehnder interferometer (MZI) optical switch, taking into account both imbalances in the arm loss and the coupler splitting ratio. The splitting ratio imbalance requirement for a given switch cross talk is summarized, which provides a guideline for the switch design. A 2 × 2 multimode interference (MMI) coupler design with low excess loss (<0.14 dB) and low imbalance (<0.13 dB) over the C-band is given. Its robustness to width variations up to ±40 nm is demonstrated. The 2 × 2 MZI switches with such an MMI are fabricated on a silicon-on-insulator (SOI) substrate using both electron beam (EB) and deep ultraviolet (DUV) lithography. The EB and DUV MMI switches exhibit cross talk of <−35 dB and <−30 dB over 40 nm, respectively. Folded configurations are used for both the silicon waveguides and the metal heaters to increase the power efficiency, resulting in a Pπ of ∼8 mW.

USE OF PULVERIZED COAL FUEL FOR PREHEATING SCRAP

Preheating of scrap in the converter is an actual area of ​​research in modern metallurgy. The growing requirements for energy efficiency and the reduction of raw material costs encourage the development of new technological solutions to increase the share of scrap metal in the charge of converter production. Traditional methods are often limited to the use of no more than 25% of scrap, which is associated with difficulties in its uniform heating and the possible formation of a liquid phase as a result of local overheating. The work evaluates the effectiveness of traditional and experimental technological solutions, such as two-tier and fuel-oxygen nozzles. The stages of ignition and burning of lump coal and pulverized coal fuel and their influence on the uniformity of scrap heating were studied. Experimental studies have shown that with a specific oxygen consumption of 1-1.35 m³/kg of pulverized coal fuel, uniform heating of scrap metal is ensured without the risk of melting the upper layers. During the use of a fuel-oxygen lance, the following features of heating scrap metal using pulverized coal fuel, which was blown in an oxygen ring shell, were discovered: - during the combustion of coal dust in an oxygen environment, due to the significant total surface of coal particles, the bulk of volatile СmНn does not have time to separate before the beginning particle ignition, and carbon burns at the same rate as volatiles. This contributes to the formation of high-temperature torches with great luminosity, which effectively affect the surface of the scrap; - the coefficient of use of blown oxygen and pulverized coal fuel is significantly higher than when using lump gas coal during heating of any duration. This is due to the greater luminosity of the formed torches, which contributes to the intensive absorption of thermal energy by the surface of the scrap; - the time required to heat the surface of the scrap metal to the specified temperature is reduced, which allows you to avoid the formation of a liquid component that can lead to undesirable consequences, such as uneven heating or damage to the converter lining. Based on the results of experimental studies, the relationship between the specific oxygen consumption and the flame temperature was established. The ability to control the temperature regime during the heating of scrap metal indicates the prospects of using a fuel-oxygen nozzle made of PVP to optimize the converter production process. For the full implementation of the technology, additional research and industrial testing are needed to optimize processes and increase production efficiency.

MATHEMATICAL MODEL OF METAL SCRAP HEATING IN THE CONVERTER WITH A COAL TORCH

Increasing requirements for energy efficiency and the level of competitiveness of domestic metal products led to the development of new technological solutions to increase the share of scrap metal in the charge of oxygen-converter melting. Data on temperature distribution in the working space of the converter and in the layer of scrap metal during its pre-heating using standard oxygen or special fuel-oxygen nozzles are limited and do not go beyond the scope of scientific assumptions. The results of numerous simulations of the process of heating metal scrap in the working space of an oxygen converter with a high-temperature torch formed by burning pulverized coal fuel in an oxygen stream using a fuel-oxygen nozzle are presented. A mathematical model of heating scrap metal in the working space of the converter with a pulverized coal torch was built and its software implementation has been done in the Visual Studio 2022 environment in the C# language. With the help of the model, a series of RO-calculations was carried out, which proved its qualitative adequacy of the process under consideration. The results of the calculation with the determination of the fields of velocities and temperatures in the working space of the converter during the heating of scrap metal are presented. It was established that the direction of heat transfer is determined by gas flows caused by a high-temperature torch. Upon reaching the metal scrap, the gas flows lead to its gradual heating, which generally corresponds to the qualitative picture of the simulated process.The dependence of the distribution of gas flows on the shape of the surface of the scrap loaded into the converter is shown. It was established that local vortices can form in the depths of the scrap surface during heating by a high-temperature torch. But the general characteristic of the gas-dynamic picture in the working space of the converter is the formation of two global vortices: one near the torch with counterclockwise rotation (in the sections shown), and the other clockwise with the formation of downward gas flows near the inner surface of the converter. These vortices mainly determine the thermal pattern in the working space of the converter and, in particular, the fact that the scrap near the wall of the converter will warm up less.

DETERMINATION OF FACTORS AFFECTING THE STABILITY OF WELDED TIPS OF OXYGEN LANCE

It has been established that the most likely cause of crack formation is differences in the chemical composition of the welding wire, the material of the Laval nozzle and the outer cage of the lance tip. For example, the difference in copper content is 6.79%. The microstructures of the weld, Laval nozzle metal, and outer lance tip rim were analyzed and compared along the cross section of the weld location. Microcracks located along the grain boundaries were detected, which is probably due to the appearance of weak compounds with low ductility and non-propagation at the grain boundaries. In the structure of welds, accumulations of oxygen inclusions along the boundaries of crystallites were found, which leads to copper embrittlement and can contribute to weld failure. Freezing a layer of converter slag with low thermal conductivity on the tip surface reduces the thermal conductivity of the formed slag metal layer and heat transfer to the cooling water. Even if there is a 1 mm layer of slag on the surface of the weld, thermal conductivity decreases by 79-95%, depending on the thickness of the slag and its properties, respectively. If there is a layer of slag on the surface of the weld, the heat transfer decreases by 51-56% (at 1 mm of slag) and by 72-88% at 20 mm, respectively.In order to prevent the formation of cracks between the Laval nozzle and the outer cage of thehandpiece, it is advisable to follow the following recommendations when performing welding operations. In the simplest case, the first welded layer should be performed using a non-consumable electrode (tungsten or graphite) in an argon or helium atmosphere, which will ensure the formation of a reliable, tight weld around the entire circumference of the nozzle. To reduce stresses in the weld, subsequent welded layers should be performed in alternating directions. A more effective option is the technology according to which, after the first weld is applied, the nozzle is connected to the tip from the inside with a partial (discrete) or continuous weld, which minimizes the likelihood of failures and can ensure the sealing of the tip when the initial cross-section of the Laval nozzles increases to the critical ignition diameter. The implementation of an internal weld will reduce mechanical loads on the external weld, especially when using metal hose expansion joints, and increase the strength of the welded joint as a whole.

Experimental and numerical investigation on photovoltaic/thermal characteristics of an integrated PV/T-PCM system with metal fin and heat exchange pipe

Experimental and numerical investigation on photovoltaic/thermal characteristics of an integrated PV/T-PCM system with metal fin and heat exchange pipe

A novel silicon carbide plate-fin heat exchanger and its thermal and hydraulic performance for SOFC cathode air preheater application

This paper focuses on a novel silicon carbide (SiC) plate-fin heat exchanger (PFHE) for the cathode air preheater application of Solid Oxide Fuel Cells (SOFCs). An innovative assembly method and a reliable connection structure with the system's metal pipelines were proposed, and then a prototype of the SiC PFHE with offset strip fins was developed. Additionally, a performance testing apparatus for the SOFC cathode air preheater was built. Based on this testing setup, experimental studies and application validation on the heat transfer and flow characteristics of the SiC PFHE were conducted. Finally, the application prospect of SiC PFHE in SOFC systems was further evaluated and compared with metallic plate heat exchangers. The results indicate that the assembly structure and test procedure of the SiC PFHE not only realize the reliable high temperature sealing, but also effectively reduce the thermal stress of SiC ceramic material. Essential parameters such as overall heat transfer coefficient, Colburn factor, and friction factor reveal consistent trends with existing literature under various operating conditions at average Reynolds number in the range from 84 to 361. The SiC PFHE has significant advantages in upper operating temperature limit and high temperature structural integrity and reliability.

Ultrafast Laser-Induced Thickness-Limited Sintering of Metal Nanoparticle Film for Ultrathin Flexible Microelectronic Devices.

Laser sintering of metal nanoparticles (NPs) has been widely used in flexible microelectronic device fabrication, wherein the sintered layer thickness is a key factor affecting the mechanical stability and conductivity. In this work, ultrathin flexible electronic circuits on flexible substrates with robust bonds and excellent conductivity have been fabricated through ultrafast laser-induced thickness-limited sintering of the metal NP film. When the laser fluence is below the damage threshold of the metal NP film, sintered layer thickness can be controlled by the laser parameters. The maximum thickness of the dense sintered NP layer is limited to 355, 421, 491, 527, and 647 nm at laser pulse durations of 0.3, 5, 10, 15, and 20 ps, respectively. This thickness-limited sintered layer is mainly determined by the plasmonic photothermal absorption of metal NPs and heat transfer within the NP layer. Due to the nonthermal process under intense ultrafast laser irradiation, the metal-polymer interaction can be further enhanced with minimal damage on substrates. The resistivity of the as-received Ag NP film decreases to 6.32 μΩ·cm after laser sintering at a pulse duration of 20 ps. Meanwhile, the relative resistance of the NP film increases to 2.7, 1.7, and 1.03 after 105 bending cycles, 500 tape peeling cycles, and water flow impinging for 60 min, respectively. This thickness-controlled ultrathin Ag NP film fabricated by ultrafast laser sintering exhibits excellent mechanical robustness and electrical conductivity, which shows great promise in ultrathin flexible microelectronic devices.

Improving the Efficiency of Applying Thermal Energy into the Formed Protective Coatings Based on Rubber Mastic

Statement of the problem. For the device of a protective coating of tubular metal made of low molecular weight oligodiene (rubber mastic), it is necessary to ensure that the required amount of thermal energy is introduced into the coating material, which, through vulcanization of rubber mastic, forms high physical, mechanical and operational characteristics of the protective layer. This result can be achieved through the development and application of highly efficient heat generating devices. Results. A method for the effective introduction of thermal energy into rubber mastic by induction heating of tubular metal is proposed, and an experimental heat generating device has been developed and constructed that implements this method and provides the necessary heat treatment modes for the composite coating material. Conclusions. The designed heat generating device, which implements an effective method of introducing thermal energy into rubber mastic, allows to ensure the necessary temperature regime in order to form a protective coating with the necessary set of physical, mechanical and operational characteristics.

Ultralow-Power Programmable 3D Vertical Phase-Change Memory with Heater-All-Around Configuration.

Recent advancements in phase-change memory (PCM) technology have predominantly stemmed from material-level designs, which have led to fast and durable device performances. However, there remains a pressing need to address the enormous energy consumption through device-level electrothermal solutions. Thus, the concept of a 3D heater-all-around (HAA) PCM fabricated along the vertical nanoscale hole of dielectric/metal/dielectric stacks is proposed. The embedded thin metallic heater completely encircles the phase-change material, so it promotes highly localized Joule heating with minimal loss. Hence, a low RESET current density of 6-8 MAcm-2 and operation energy of 150-200 pJ are achieved even for a sizable hole diameter of 300nm. Beyond the conventional 2D scaling of the bottom electrode contact, it accordingly enhances ≈80% of operational energy efficiency compared to planar PCM with an identical contact area. In addition, reliable memory operations of ≈105 cycles and the 3-bits-per-cell multilevel storage despite ultrathin (<10nm) sidewall deposition of Ge2Sb2Te5 are optimized. The proposed 3D-scaled HAA-PCM architecture holds promise as a universally applicable backbone for emerging phase-change chalcogenides toward high-density, ultralow-power computing units.

Enhancing resistance welding strength of carbon fiber/polycaprolactam thermoplastic composites through coupling agent‐modified metal heating elements

AbstractThis study investigates the impact of coupling agent‐modified resistance welding heating elements on the welding strength of carbon fiber‐reinforced polyamide 6 (PA6) thermoplastic composites. Silane coupling agent KH550 and titanate coupling agent UP‐201 were used to modify heating elements made of 304 stainless steel mesh. Optimal modification parameters for KH550‐modified stainless steel mesh (SSM) were determined using orthogonal experiments, resulting in maximum single lap shear strength (LSS) of 17.05 MPa under specific welding conditions. Comparative tests demonstrated the enhancement effect of UP‐201‐modified SSM on LSS. Additionally, two experimental schemes were used to study the synergistic enhancement effect of KH550 and UP‐201 on the LSS of resistance welded joints. The findings indicate that both coupling agents improve the welding strength, with significant differences in their individual and combined effects.Highlights This study explores carbon fiber reinforced Nylon 6, an innovative thermoplastic. Analyzed effects of modified heating elements on joint shear strength. Examined silane and titanate coupling agents' effects on weld joint shear strength. Investigated synergistic effects of silane and titanate agents on weld joint strength. Investigated the synergistic enhancement mechanism of silane and titanate agents.

Tunable Fano resonances at 2 μm waveband based on a single microring resonator

Abstract Development of silicon photonic devices for the 2 μm waveband is urgent since the 2 μm waveband has been considered as a potential communication window for next-generation optical communications. Asymmetric Fano resonances are very promising in the development of devices such as optical switches, sensors, and modulators for the 2 μm waveband. In this paper, a Fano resonance at the 2 μm waveband is theoretically realized by using a silicon-based microring resonator and the thermo-optic effect is employed to tune it. Utilizing this single microring resonator structure instead of the present coupled microring resonator structures, we achieve the Fano resonance with an extinction ratio of 30.5 dB and a slope ratio of 69.3 dB nm−1 at the 2 μm waveband. The metal heater and graphene heater are designed and optimized to achieve the Fano tuning. The thermal-optical tuning efficiencies are 0.46 nm mW−1, 0.61 nm mW−1 and 1 nm mW−1 for the metal heater, the metal heater with air adiabatic slots, and the graphene heater, respectively. This work provides an effective scheme for the formation and tuning of the Fano resonance at the 2 μm waveband, which is conducive to the development of devices and optical communication systems at the 2 μm waveband.

Portable paper-based multicolor sensor for sensitive on-site detection of organophosphorus pesticides using a high-efficiency Au+-induced gold nanobipyramids aspect ratio regulation strategy

On-site visual detection of organophosphorus pesticides (OPs) is crucial for safeguarding environmental and food safety. This study presents a robust, sensitive, and portable paper-based multicolor sensor (PMS) for the on-site detection of OPs. The PMS involves a novel Au+-induced gold nanobipyramids (AuNBPs) morphology transformation reaction within a paper-based analytical device (PAD) coupled with a bienzymatic hydrolysis system. The Au+-induced reaction sensitively regulates the aspect ratio of AuNBPs through Au+ disproportionation, which decreases the length of AuNBPs and simultaneously increases the width, accompanied by distinct multicolor changes. Upon performing in the PAD incorporating easily-prepared AuNBPs-deposited nylon membranes, a metal heater, and an oscillator, the Au+-induced reaction exhibits excellent reaction sensitivity, efficiency, reproducibility, AuNBPs stability, and color uniformity. In the bienzymatic hydrolysis system, acetylcholinesterase (AChE) and choline oxidase hydrolyze acetylcholine to product H2O2, which consumes tris(2-carboxyethyl)phosphine hydrochloride (TCEP), maintaining free Au+ for the disproportionation in the Au+-induced system, while the presence of OPs inhibits AChE activity, preserving TCEP to chelate Au+ and hindering the disproportionation. Under optimized conditions, the PMS exhibited eight dichlorvos concentration-corresponding color changes with a visual detection limit of 30 μg/L and a spectrometry detection limit of 8.1 μg/L. It achieved recoveries of 85.4–101.9 % in river water, drinking water, rice, and Chinese cabbage samples with relative standard deviations (n = 5) < 6 %. Thus, this study offers a portable, sensitive, reliable, and practical on-site detection method for OPs. Additionally, the proposed Au+-induced AuNBPs morphology transformation system within the PAD offers promising alternative strategies for developing other AuNBPs-based colorimetric sensors.

An Investigation of Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating.

Recent progress has seen multiple Ta2O5 polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta2O5 particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an 18O2 atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta2O5 phase or a similar, but not identical, crystalline β-Ta2O5 phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic "H-Ta2O5" phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta2O5. Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta2O5. We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air.

Enhancing the Lap Shear Performance of Resistance-Welded GF/PP Thermoplastic Composite by Modifying Metal Heating Elements with Silane Coupling Agent.

Thermoplastic composites are gaining widespread application in aerospace and other industries due to their superior durability, excellent damage resistance, and recyclability compared to thermosetting materials. This study aims to enhance the lap shear strength (LSS) of resistance-welded GF/PP (glass fiber-reinforced polypropylene) thermoplastic composites by modifying stainless steel mesh (SSM) heating elements using a silane coupling agent. The influence of oxidation temperature, solvent properties, and solution pH on the LSS of the welded joints was systematically evaluated. Furthermore, scanning electron microscopy (SEM) was utilized to investigate the SSM surface and assess improvements in interfacial adhesion. The findings indicate that surface treatment promotes increased resin infiltration into the SSM, thereby enhancing the LSS of the resistance-welded joints. Treatment under optimal conditions (500 °C, ethanol solvent, and pH 11) improved LSS by 27.2% compared to untreated joints.

A novel nucleic acid extraction system integrating a switching valve-assisted microfluidic cartridge and a constant pressure pump

BackgroundNucleic acid extraction (NAE) is essential in molecular diagnostics, genetic engineering, and DNA sequencing. While advances in switching valve-assisted, self-contained microfluidic (S2M) cartridges have improved the NAE processes, challenges persist in streamlining workflows, reducing processing times, and enhancing multi-target detection. Achieving these objectives requires precise control of on-chip fluid dynamics and efficient transfer of nucleic acid solutions (NAS) to detection areas. However, research on novel S2M cartridge designs and compatible fluid control systems is still limited. ResultThis study presented an innovative NAE system that integrated an S2M cartridge, a constant pressure (CP) pump, a metal heating bath, a rotating lever, and a magnet. The S2M cartridge contained the reagents for both NAE and detection, while the CP pump provided stable, precise, and rapid fluid delivery, outperforming traditional peristaltic and injection pumps, especially for handling small volumes and reducing pulsation. A custom rotating lever connects reagent chambers, facilitating mixing, cleaning, elution, and NAS transfer. This system showed advantages over manual methods, achieving all processes in 20 min. The CP pump-assisted S2M cartridge enabled rapid MBs re-suspension with a recovery rate of 80 %. The system's sensitivity, repeatability, and ease of use were also confirmed. The NAE system can extract Escherichia coli DNA (50 CFU mL^-1) from food and serum samples and viral DNA (HBV, HCV, HIV) at 200 copies mL^-1 from serum samples. SignificanceThis study highlighted the need for an efficient fluid system in the S2M cartridge for stable NAE. By streamlining NAE and facilitating on-chip reagent preparation, the system enhanced point-of-care diagnostics. Although manual steps remain, the CP pump effectively managed fluid processes, paving the way for automated pathogen detection. Moreover, when combined with visual detection reagents, the NAE system showed promise as a direct molecular diagnostic tool.

Analysis of the aerothermal performance of modern commercial high-pressure turbine rotors using different levels of fidelity

In the field of design and optimization of sophisticated geometries such as film-cooled turbine blades of modern jet engines, Computational Fluid Dynamics (CFD) simulation is commonly employed. As the pursuit for higher turbine entry temperatures intensifies, it becomes crucial for computational analyses to offer accurate predictions of metal temperatures and heat transfer coefficients on these critical components. This study investigates the impact of key physical factors that characterize the operation of these components on the accuracy of the computational model. In particular, the effects of including the exchange of thermal energy between the fluid and solid domains, as well as modelling the unsteady interaction between the rotor and stator are studied. The research focuses on a fully featured one-and-a-half stage high-pressure turbine of a commercial jet engine, utilizing proprietary software for conducting 3D Reynolds-Averaged Navier-Stokes flow simulations. To model the fluid-solid thermal interaction, steady-state Conjugate Heat Transfer (CHT) simulations are performed. The CHT results are then compared with experimental data obtained from a thermal paint test, achieving good levels of agreement. Additionally, phase-lag simulations are executed under adiabatic-wall conditions to evaluate the influence of stator-rotor interaction on near-wall gas temperatures. This work shows that, by modelling the periodic unsteadiness at the stator-rotor interface with a phase-lag technique, the maximum near-wall gas temperature prediction is significantly increased, sometimes more than 100K, with respect to the steady-state model one. Findings from this work also suggest that simplified “strip” source terms used to model the presence of film cooling hole rows on the surface of a blade can be used with satisfactory accuracy only for nominal conditions. The mass flows delivered by each source strip should not be linearly scaled based on mainstream quantities for use in different conditions, but they should be recalculated from scratch for the new conditions.

Experimental Study on Startup Performance of a High-temperature Liquid Metal Heat Pipe with Fins

Experimental Study on Startup Performance of a High-temperature Liquid Metal Heat Pipe with Fins

Numerical method research and characteristics analysis on frozen start-up process of high-temperature heat pipe

Future space exploration technology requires a long-life and reliable power source that is not reliant on solar energy. Space micro-reactors are able to meet this need, with Heat Pipe Cooled Reactors (HPR) emerging as a notable type of space micro-reactor that has attracted widespread attention in recent years. The HPR utilizes high-temperature alkali metal heat pipes for heat transfer, which presents certain complexities due to the solid state of the alkali metals working medium at room temperature. This results in a three-phase transition during the high-temperature heat pipes start-up process, which significantly impacts the heat transfer characteristics and dynamic behavior of the HPR start-up process. Consequently, thorough research is necessary in this area. Numerical simulation is a crucial tool that can effectively analyze, predict, and guide experiments. This article utilizes the Finite Volume Method (FVM) to develop a simulation code for high-temperature heat pipe frozen start-up. Various physical models are integrated to describe different components of the heat pipe: the container is represented by a two-dimensional axisymmetric heat conduction equation, the wick region utilizes a Fixed Grid Method (FGM) to depict the melting process of the medium, and the vapor channel is described through a two-dimensional axisymmetric compressible laminar flow. The wick region and vapor channel are coupled through the evaporation and condensation of the medium. For the vapor channel, numerical methods such as SIMPLE and PISO are used for solving. Adaptive time step and OpenMP acceleration are employed in the code to enhance computational efficiency. Finally, by comparing the calculated results with experimental data, the feasibility and accuracy of the code are assessed, highlighting special phenomena during the start-up process. The findings confirm that the developed code accurately predicts parameter changes during start-up, and can serve as a heat pipe analysis module for multi-physics coupling analysis of HPR.

Numerical simulation of electrically-pumped overgrown III-V microwire lasers on silicon

Electrically-pumped III-V lasers on Si by aspect ratio trapping (ART) techniques have been a promising candidate for Si-based light sources. Although the lasers based on the ART approach enable large-scale integration and are compatible with complementary metal-oxide semiconductor processes, the sub-micron size laser structure suffers from severe metal absorption loss and heat accumulation. In this paper, we propose a novel Si-based III-V multi-quantum well laser by ART methods. The overgrowth of III-V microwires is adopted, with additional {110} quantum wells (QWs) generated during epitaxy. Through numerical simulation, the mode loss of the overgrowth structure is reduced from 3.59 dB/cm to 0.96 dB/cm, the threshold current is decreased by 42.5% and the output power is increased by 91.7% under pulsed conditions. Due to the growth of QWs on {110} planes, the injection efficiency of the device increases, leading to an improvement of performance. The effects of temperature and cavity length on the lasing characteristics of the device under continuous wave (CW) conditions are also analyzed that the proposed structure can realize CW lasing at room temperature. Moreover, the device deterioration caused by growth defects is discussed, which can be improved by high reflection coating. The suggested Si-based overgrowth III-V microwire laser has great potential to integrate high-density electrically-pumped light sources for silicon photonics.