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We develop the theoretical foundation to determine the thermal conductivity of a single nanowire by using the optical contrast of the metallic and insulating domains of a VO 2 nanowire excited with either a temperature difference or a laser beam. Considering the temperature dependence of the VO 2 thermal conductivity, the heat flux and the temperature profile along a VO 2 nanowire are obtained and used to derive explicit expressions for the position of the metal/insulator domain interface as a function of the thermal excitation. This relation determines the variations of the metallic and insulating domains' lengths, which can be employed to retrieve the thermal conductivity of a single nanowire bonded to a VO 2 one. Furthermore, the advantages and disadvantages of each thermal excitation are discussed along with the appearance of invariants driving the one-dimensional nonlinear heat conduction along VO 2 nanowires. [ABSTRACT FROM AUTHOR]

We develop the theoretical foundation to determine the thermal conductivity of a single nanowire by using the optical contrast of the metallic and insulating domains of a VO 2 nanowire excited with either a temperature difference or a laser beam. Considering the temperature dependence of the VO 2 thermal conductivity, the heat flux and the temperature profile along a VO 2 nanowire are obtained and used to derive explicit expressions for the position of the metal/insulator domain interface as a function of the thermal excitation. This relation determines the variations of the metallic and insulating domains' lengths, which can be employed to retrieve the thermal conductivity of a single nanowire bonded to a VO 2 one. Furthermore, the advantages and disadvantages of each thermal excitation are discussed along with the appearance of invariants driving the one-dimensional nonlinear heat conduction along VO 2 nanowires. [ABSTRACT FROM AUTHOR]

This paper established a three-dimensional transient MHD model of a high-current multi-component vacuum arc under a transverse magnetic field (TMF) to simulate the dynamic characteristics of plasma parameters in the uniform motion mode of a contracted arc under lower TMF. The model considered the ionization–recombination process among the multi-components and used the P1 model to calculate the thermal radiation losses. The simulation results show that the ion number density of The TMF arc is on the order 1024 m−3, and when the plasma temperature reaches 4.3 eV, the effects of thermal radiation cannot be ignored. The majority of the plasma from the cathode and anode undergo acceleration and then deceleration before finally intersecting at the center of the arc, creating an extreme value of the density and the pressure, where a large amount of kinetic energy is converted into internal energy. The arc will be bent and deflected under the action of the ampere force, and the deflection of Cu3+ is especially obvious. The TMF affects the collision strength of the jet in the intersection area and, thus, affects the ion density, in which the change of Cu2+ is dominant. The ionization–recombination process of ions is mainly determined by the electron temperature, which is affected by the arc current. As the current decreases, Cu1+ increases and Cu2+ and Cu3+ decrease, and the change in ionization rate is the main reason for the change in the proportion of each ionic component; the heat flux density to the anode and cathode is on the order of 1010 W/m2, which heats the front of the arc and ensures the stable movement of the arc. Meanwhile, due to the high ion number density, the ion heat flux accounts for the main part of the heat flux, and the anode exhibits a higher proportion of ion heat flux. [ABSTRACT FROM AUTHOR]

This paper presents BubbleID, a sophisticated deep learning architecture designed to comprehensively identify both static and dynamic attributes of bubbles within sequences of boiling images. By amalgamating segmentation powered by Mask R-CNN with SORT-based tracking techniques, the framework is capable of analyzing each bubble's location, dimensions, interface shape, and velocity over its lifetime and capturing dynamic events such as bubble departure. BubbleID is trained and tested on boiling images across diverse heater surfaces and operational settings. This paper also offers a comparative analysis of bubble interface dynamics prior to and post-critical heat flux conditions. [ABSTRACT FROM AUTHOR]

To address the challenges faced by designers of multi-field coupled cooling systems for high heat flux chips, this paper proposes a "near-source" microchannel cooling strategy and establishes a thermal–flow-force electrically coupled model for chips. The effects of chip Joule heat and cooling water flow rate on the cooling performance with respect to multi-field coupling effects were studied. The impact of multi-field coupling effects was revealed, and a method for enhancing microchannel cooling performance in light of multi-field coupling effects is proposed. The results indicated that considering multi-field coupling effects in the microchannel cooling process leads to a deterioration in the thermal performance of chips, accompanied by a significant increase in electrical fluctuations and thermal deformation amplitude. Compared to chips upstream of the cooling water, chips downstream subjected to thermal cascade effects were more sensitive to multi-field coupling effects. Moreover, the temperature variance index, output current, and strain energy density of high heat flux chips were positively correlated with Joule heat but inversely proportional to the Reynolds number of the cooling water for cases in respect of multi-field coupling effects. Additionally, serpentine microchannels maximized the operational performance of high heat flux chips by reducing temperature of chip by up to 55.1%, decreasing strain energy density by 96.7%, and increasing input potential by 120%. [ABSTRACT FROM AUTHOR]

(Hf 1/3 Zr 1/3 Ti 1/3)C and (Hf 1/2 Zr 1/3 Ti 1/6)C middle-entropy carbide ceramics were successfully prepared using polymer-derived ceramic method. The study examines the microstructural evolution, phase composition changes, and ablation behavior of these two ceramic materials when subjected to an oxyacetylene flame at varying heat fluxes. The experimental results indicate that at a heat flux of 5 MW/m2, the mass and linear ablation rates of (Hf 1/3 Zr 1/3 Ti 1/3)C ceramic are −0.837 mg/s and 1.857 μm/s, respectively. In contrast, (Hf 1/2 Zr 1/3 Ti 1/6)C ceramic exhibits significantly superior ablation resistance, with rates of −0.315 mg/s and −0.745 μm/s. This underscores the critical role of compositional adjustments in enhancing the ablation performance of the ceramic. During ablation, (Hf 1/2 Zr 1/3 Ti 1/6)C forms an optimal amount of (Hf, Zr)TiO 4 healing phase, which contributes to the development of a stable oxide film consisting of an m-(Hf, Zr, Ti)O 2 oxide skeleton and a (Hf, Zr)TiO 4 liquid phase. This structure effectively resists high-velocity airflow erosion and oxygen penetration. Additionally, the formation of a carbonaceous oxide interlayer strengthens the bond between the oxide layer and the carbide matrix, further improving the material's ablation resistance. The study highlights the significant influence of compositional ratio control on the ablation behavior and mechanisms of carbide ceramics, providing a robust foundation for their application in high-temperature thermal protection technologies. [ABSTRACT FROM AUTHOR]

The effect of longitudinal ventilation on hydrogen jet fires was investigated in tunnel. The extended flame length, temperature, and thermal radiation flux were measured for nozzle diameters (1∼5.12 mm), tilt angles (30–60°) and pressures (1–4 MPa). The results indicate that the longitudinal wind speed has a suppressive effect on the extended flame length on the ground. The extended flame length on the ground decreases with increasing wind speed. Longitudinal ventilation also has a suppressive effect on the gas temperature around the flame, and the maximum temperature difference decreases with increasing wind speed. Based on the geometric model of the extended flame, a fitted relationship between the dimensionless extended flame length and the longitudinal wind speed was established. Additionally, a fitted relationship between the dimensionless peak flame temperature and the normalized position was also proposed. • Longitudinal ventilation hydrogen jet fire experiments were conducted in a model tunnel. • Longitudinal ventilation effects on flame behavior, temperature and radiation were focused. • The formulas of dimensionless flame length and temperature were proposed. • The maximum temperature difference decreases with increasing wind speed. [ABSTRACT FROM AUTHOR]

High-pressure liquid hydrogen pumps are the key equipment for the large-scale and efficient transfer of liquid hydrogen. Accurately predicting the in-cylinder heat transfer is crucial for optimizing the performance of high-pressure liquid hydrogen pumps. This paper numerically studies the unsteady heat transfer and fluid flow in the cylinder of a reciprocating liquid hydrogen pump, considering thermal conduction in the cylinder wall. The thermal conduction process in the cylinder wall of the high-pressure compression cylinder and its impact on the temperature distribution and heat flux are analyzed. Additionally, the effects of cylinder wall materials on temperature distribution, fluid flow, and heat transfer are studied. Finally, the calculation results are compared with the predictions of three existing empirical correlations for in-cylinder heat transfer. Among these, Annand's correlation accurately predicts the Nusselt number in comparison with the calculation results. This work can provide theoretical support for the thermal design and structural optimization of high-pressure liquid hydrogen pumps. • A CFD model of thermal conduction in the cylinder wall is proposed. • A high-temperature zone of 24 K forms due to in-cylinder heat transfer. • Thermal diffusivity of wall material impacts the in-cylinder heat transfer. • SUS316 is more beneficial for enhancing the pump performance. • Annand's correlation can accurately predict in-cylinder heat transfer. [ABSTRACT FROM AUTHOR]

This study numerically evaluated Al 2 O 3 , SiO 2 , and their hybrid nanofluids (HNFs) at mixing ratios of 10:90, 30:70, and 50:50 in a water–BioGlycol (BG) mixture at a 0.5% volume concentration to evaluate the thermal–hydraulic performance of these coolants in proton-exchange membrane fuel cell (PEMFC) stacks. A three-dimensional conjugate heat transfer model was developed and analyzed under variable heat flux conditions, with simulations performed using various Reynolds numbers (Re; 50–350) and volume flow rates (VFRs; 400–2000 mL/min). The results indicated that associating the thermal performance of HNFs to Re is inaccurate owing to the influence of HNF properties. Under fixed Re conditions, HNFs exhibited superior thermal performance, whereas, at constant VFRs, they showed a decline in thermal performance. HNFs require substantially higher pumping power than the base fluid BG40% to maintain the PEMFC stack temperature. Therefore, BG40% is more effective in maintaining PEMFC temperature stability and efficiency. • Hydrothermal performance of Al 2 O 3 –SiO 2 HNFs in a PEMFC is numerically studied. • Relating HNFs' thermal performance to Re alone can lead to inaccurate conclusion. • BG40% offered the best hydrothermal performance among all considered coolants. [ABSTRACT FROM AUTHOR]

Understanding the thermal comfort and safety of diverse populations within indoor settings requires a quantitative understanding of the primary heat exchange pathways between occupants and their surroundings: radiation and free convection. Thus far, however, free convective heat transfer coefficients have only been determined for the average Western adult. To this end, we investigated how variation in body shape impacts free convection heat transfer using an experimentally validated numerical model. The multiphysics model was compared against experiments conducted using the thermal manikin ANDI ("Advanced Newton Dynamic Instrument") in a climate-controlled enclosure across five air-to-skin temperature differences ranging from 4.9 to 13.9°C. The difference between measured and simulated heat fluxes for the whole body, and per anatomical region, was typically <5%, occasionally reaching 15–20%, for some body regions due to physical features not modeled in the virtual ANDI model. Using the validated model, we simulated free convection around a family, or diverse group, of virtual manikins representing the 1st to 99th percentile body mass index (BMI) and height variation in the United States adult population. Our results show that the free convection heat transfer coefficient is independent of human sex and height but decreases slightly with increased BMI. However, the variation from the average manikin in the whole body and regional free convection coefficients with BMI was small, not exceeding 8% and 16%, respectively. Furthermore, our regression coefficients and exponents can be derived from the theorical correlation for free turbulent convection from a vertical plate, which also explains the observed independence of the heat transfer coefficient from the manikins' height. Overall, these findings demonstrate the general applicability of using an average body shape in indoor thermal audits and/or overheating risk assessments to understand thermal comfort and heat stress. The results and valid application of the model support critical insights for human health, productivity, and well-being connected to heat and cooling in buildings. [ABSTRACT FROM AUTHOR]

The thermal oxidation stabilization of polyacrylonitrile (PAN) copolymer is a highly exothermic process. It significantly impacts the quality of the finished PAN‐based carbon fiber, which is often addressed by adding appropriate comonomers. This paper synthesized guanidine crotonate (GCA) as a comonomer and copolymerized with acrylonitrile (AN) to prepare P(AN‐GCA). DSC analysis revealed that when compared to PAN and P(AN‐CA) copolymers, the initial exothermic temperature, maximum exothermic heat flux, and heat flux of P(AN‐GCA) copolymer were greatly reduced. FT‐IR spectroscopy showed that the degree of pre‐oxidation increased with the increasing comonomer GCA content, indicating that the addition of comonomer GCA could promote PAN pre‐oxidation cyclization and improve the copolymer's degree of pre‐oxidation. The activation energies of PAN and P(AN‐GCA) were 160 and 126 KJ/mol, respectively. It was shown that the addition of GCA could effectively reduce the activation energy of the cyclization reaction of the polymer while simultaneously promoting it. TGA analysis shows that the introduction of GCA improves the copolymer's thermal stability, and the yield at 800°C is more than 54%, which is at least 19% higher than PAN homopolymer. P(AN‐GCA) has the potential to be carbon fiber precursor. [ABSTRACT FROM AUTHOR]

Vegetation characteristics significantly influence the impact of wildfires on individual building structures, and these effects can be systematically analyzed using heat transfer modelling software. Close-range light detection and ranging (LiDAR) data obtained from uncrewed aerial systems (UASs) capture detailed vegetation morphology; however, the integration of dense vegetation and merged canopies into three-dimensional (3D) models for fire modelling software poses significant challenges. This study proposes a method for integrating the UAS–LiDAR-derived geometric features of vegetation components—such as bark, wooden core, and foliage—into heat transfer models. The data were collected from the natural woodland surrounding an elevated building in Samford, Queensland, Australia. Aboveground biomass (AGB) was estimated for 21 trees utilizing three 3D tree reconstruction tools, with validation against biomass allometric equations (BAEs) derived from field measurements. The most accurate reconstruction tool produced a tree mesh utilized for modelling vegetation geometry. A proof of concept was established with Eucalyptus siderophloia, incorporating vegetation data into heat transfer models. This non-destructive framework leverages available technologies to create reliable 3D tree reconstructions of complex vegetation in wildland–urban interfaces (WUIs). It facilitates realistic wildfire risk assessments by providing accurate heat flux estimations, which are critical for evaluating building safety during fire events, while addressing the limitations associated with direct measurements. [ABSTRACT FROM AUTHOR]

This study investigates the use of h-BN particles as fillers, focusing on tailoring surface chemistry to enhance the thermal conductivity of epoxy composites. By enriching the interface between h-BN particles with amino-silane groups and the epoxy matrix through controlled surface modification, thermal performance, and interfacial bonding were improved. To achieve a high degree of functionalization, h-BN particles were oxygenated to 13.6 atomic percent (at. %) through thermal treatment, followed by reduction using 3-amino-propyl-3-ethoxy-silane (APTES), which increased the amino content by 3.5% at. % under optimized reaction conditions. During composite manufacturing, 10 wt.% functionalized h-BN particles were reinforced into the epoxy matrix, increasing bulk thermal conductivity by 53%, from 0.2 W/mK to 0.34 W/mK. Heat flux simulations with ANSYS confirmed the interface interactions and thermal performance, with silanized h-BN achieving the highest heat flux of 70 W/mm2, aligning well with experimental results. While silanization improved thermal conductivity by strengthening interfacial bonding between h-BN and the epoxy matrix, it introduced brittleness, making the composites stiffer and more fragile. However, the silanized h-BN composite showed a 57.14% increase in toughness compared to neat h-BN, while the highest flexural modulus of 4126 MPa was achieved with neat h-BN. [ABSTRACT FROM AUTHOR]

In this paper, by means of two general lemmas applicable to a wide variety of cases, we present a general formulation for the stability numbers associated with the thermoelastic Bresse system with heat flux given by Cattaneo's law and use it to show exponential stability of shear-damped versions of this system. [ABSTRACT FROM AUTHOR]

This study investigates the Walters' B fluid in two-dimensional boundary layer flow through a porous medium of an exponentially stretching sheet. In the face of Newtonian heating, the Cattaneo-Christov heat flux model which expresses the thermal relaxation time is examined together with heat generation/absorption for the heat equation. The resulting equations of the model are resolved into non-dimensional forms, which are further performed by the Homotopy Analysis Method. The key findings along with the result obtained demonstrated that the Cattaneo-Christov heat flux which depicts the thermal relaxation time makes low the temperature field, indicating that the neighbouring particles crave for more time for the heat to fall deeper, while heat generation/absorption, as well as Newtonian heating, permit the quick infiltration of thermal sequel to the quiescent fluid which in turn aids the dryness of the materials. Meanwhile, the variation in local Weissenberg number triggers viscoelasticity whose application is crucial for the processing of the polymer in industries and other related disciplines. [ABSTRACT FROM AUTHOR]

3-D numerical simulations based on diffusion combustion technology were employed to optimize the multi-stage air/gas supply system in a coke oven battery with 7.1 m coking chambers. In the heating flues, the Eddy-Dissipation Concept (EDC) model and the ideal gas model were utilized to numerically investigate diffusion combustion. What is more, the radiation between the flue gas and the silicon brick was calculated using the Discrete Ordinates (DO) model. After validating the reliability of the model with field-measured data, insights into the temperature field and gas flow in the heating flue, and heat flux distribution over the heating wall were obtained. To characterize the vertical heating uniformity, an index of the standard deviation of the heat flux over the vertical heating walls was proposed. By optimizing the multi-stage air/gas supply design of heating flues, the vertical heating uniformity was improved by 60% according to the index values. The approach developed in this work can be a useful tool for the design of large-capacity coke oven batteries at different scales. [ABSTRACT FROM AUTHOR]