Heat Conduction Research Articles

A Novel Case of Cooling and Heating in Rectangular Lid-Driven Cavities: Interplay of Richardson Numbers in Streamlines and Isotherms

The thermal and dynamic behavior of SiO2 nanofluid was studied in a rectangular lid-driven cavity using the finite difference method. A non-adiabatic lid and a hot section at the bottom wall were considered in different heating and cooling cases. Three novel study cases were studied: a standard temperature at Th (heat conduction through the left-side walls), a high hot temperature, 2Th (heat conduction through the left-side walls), and a 2Tc high cold temperature (heat conduction through right-side walls). The Richardson number was varied between 10 and 100, and the lid direction. With a Richardson number of 10, the streamlines in the different cases tended to the formation of a central vortex with small vortices on the side walls, and the isotherms tended to a central one near the lower wall’s heated section and the homogenized temperature in the center of the cavity. At a Richardson number of 100, the streamlines produced a division in the cavity through a central vortex due to the heating of the bottom wall; this affected the isotherms, generating a prominent one in the center of the cavity and others near it. The generating decreased in the temperature near the bottom and top walls but increased in the middle of the cavity. The standard temperature case tended to behave similarly to the high cold temperature case but presented different temperatures, while the high hot temperature case generally maintained a slightly different behavior. These effects were more noticeable with the lid direction opposite X.

Shannon Entropy in Uncertainty Quantification for the Physical Effective Parameter Computations of Some Nanofluids

The main aim of this study is probabilistic computer simulation of the effective physical parameters of fluids containing nanoparticles. A deterministic model following the rule of mixtures and some semi-empirical formulas are employed to calculate effective density, heat conductivity, heat capacity, as well as viscosity for the given nanofluid. This models is randomized here using the Monte-Carlo simulation apparatus for estimation of the Shannon entropy of all these physical parameters, which is the crucial novelty of this study. The volume fraction of the nanoparticles is assumed for this purpose as the Gaussian uncertainty source with the given first two moments. The basic probabilistic characteristics of the nanofluids’ homogenized parameters have also been determined here for some validation of Shannon entropy variations in addition to the statistical disorder of the nanoparticle fraction. These research findings contribute to advancing nanofluidic and microfluidic research, offering robust tools for uncertainty analysis and enhancing the reliability of physical parameter predictions in applications requiring high numerical and/or experimental precision.

Anisotropic Heat Conduction of Silicon Nanocube through Strain Gradient Engineering.

Precise control of directional heat flow is essential for advancing applications such as microchip cooling and building thermal regulation. However, existing methods often face challenges related to manufacturing complexity, structural instability, and limited reversibility. Here, we present strain-gradient-induced crystal symmetry breaking as an effective strategy to achieve anisotropic heat conduction. We model a uniaxially bent silicon nanocube and predict an anisotropy ratio of 1.20 at a strain gradient of 0.44%/nm (12% bending strain). This anisotropy arises from two distinct types of strain within the bent lattice: static strain along the axial direction, which significantly impedes heat conduction, and dynamic strain in the transverse directions, which poses a minimal effect on heat flow. The static strain broadens the phonon spectrum and induces phonon overdamping, thereby enhancing scattering and leading to marked reductions in the thermal conductivity. These findings highlight strain-gradient-induced phonon spectrum engineering as a reversible and robust method for directional thermal regulation.

Numerical simulation of fluid–structure interaction for solid rocket engine nozzle ablation

When a solid rocket engine is ignited, the throat lining of the nozzle is prone to chemical ablation owing to high-temperature gas erosion, resulting in thrust loss. In this paper, a coupled fluid–solid model for thermochemical ablation on the nozzle wall is established based on the multi-component Navier–Stokes equations, SST k-ω turbulence model, finite-rate chemical reaction model on the nozzle wall, variable transport properties of the nozzle material, and the heat conduction equation. Compared with the experimental data, the maximum error of the calculated ablation rate was 4.37%, validating the effectiveness of the model. Subsequently, the effects of different combustion chamber components, pressures, and temperatures on the ablation rate of the carbon–carbon (C/C) throat lining were studied. The results indicate that the temperature at the nozzle throat was the highest, resulting in the maximum ablation rate. As the Al mass fraction at the nozzle inlet increased, the thermochemical ablation rate of the nozzle decreased with a lower oxidizer mass fraction. The inlet pressure and temperature of the nozzle were positively correlated with the ablation rate, with the temperature having a more significant impact than the pressure. These findings provide theoretical guidance for the thermal protection design of rocket engine nozzles.

Heat conduction dynamics: a study of lie symmetry, solitons, and modulation instability

Heat conduction dynamics: a study of lie symmetry, solitons, and modulation instability

Physical and Mathematical Modeling of the Process of Warming of the Greenhouse Soil

Statement of the problem. One of the main components of heat exchange in summer and seasonal greenhouses is investigated, i. e., the distribution of the temperature field in the heated soil. Results. Under the assumption of homogeneity of the semi-bounded space, which is a soil massif, the heat conduction equation with constant thermal and physical parameters is solved. It is shown that using the principle of superposition of solutions, as well as the properties of linearity and homogeneity of the equations, it is possible to apply (in order to study the dynamics of the temperature field in the closed ground of summer greenhouses) the method of heat waves with periodically changing boundary forces. In addition, the effectiveness of the application of mathematical physics methods using the dimension method in finding a partial solution to the heat conduction equation in order to model the process of soil heating in the conditions of a seasonal greenhouse is shown. Conclusions. Analytical expressions are obtained that allow us to determine the degree of heating of the soil layer of the summer greenhouse depending on the fluctuations of the temperature wave. For the soil of seasonal greenhouses, an expression was obtained for the change of the temperature gradient on the surface of the soil depending on the time of heating.

Numerical Study of Hydrate Dissociation and Heat Stimulation by Hot Water Injection in Gas Hydrate Reservoirs

ABSTRACTHot water injection has been a simple and promising method of thermally stimulating the extraction of hydrates, which promotes the dissociation of natural gas hydrates and improves gas production. However, the temperature region influenced by injecting hot water requires further research and evaluation. In this study, a computational model of the temperature field in the hydrate reservoir during hot water injection with the finite volume method, considering coupled gas–liquid two‐phase flow, heat conduction, and hydrate dissociation, was developed. The model focuses on hot water injection vertical wells completed with slotted liners in the Shenhu Sea area hydrate reservoir, which can consider the heterogeneity of porosity, permeability, and saturation. It also analyzes the effects of injection volume, injection rate, hot water temperature, and other factors on the variations in temperature and pressure distribution. The results indicate that selecting the appropriate injection volume, the temperature of hot water, and the injection rate can promote hydrate decomposition and expand the range of heat stimulation reservoir temperature. Reservoir heterogeneity leads to heterogeneity of the hydrate dissociation front and temperature influence range, and the influence range of heat stimulation is larger than homogeneous reservoir.

Computer Simulation and Speedup of Solving Heat Transfer Problems of Heating and Melting Metal Particles with Laser Radiation

The study of the process of laser action on powder materials requires the construction of mathematical models of the interaction of laser radiation with powder particles that take into account the features of energy supply and are applicable in a wide range of beam parameters and properties of the particle material. A model of the interaction of pulsed or pulse-periodic laser radiation with a spherical metal particle is developed. To find the temperature distribution in the particle volume, the non-stationary three-dimensional heat conductivity equation with a source term that takes into account the action of laser radiation is solved. In the plane normal to the direction of propagation of laser radiation, the change in the radiation intensity obeys the Gaussian law. It is possible to take into account changes in the intensity of laser radiation in space due to its absorption by the environment. To accelerate numerical calculations, a computational algorithm is used based on the use of vectorized data structures and parallel implementation of operations on general-purpose graphics accelerators. The features of the software implementation of the method for solving a system of difference equations that arises as a result of finite-volume discretization of the heat conductivity equation with implicit scheme by the iterative method are presented. The model developed describes the heating and melting of a spherical metal particle exposed by multi-pulsed laser radiation. The implementation of the computational algorithm developed is based on the use of vectorized data structures and GPU resources. The model and calculation results are of interest for constructing a two-phase flow model describing the interaction of test particles with laser radiation on the scale of the entire calculation domain. Such a model is implemented using a discrete-trajectory approach to modeling the motion and heat exchange of a dispersed admixture.

Spontaneous heat current and ultra-high thermal rectification in asymmetric graphene: a molecular dynamics simulation

Non-equilibrium molecular dynamics simulations reveal the existence of a spontaneous heat current (SHC) in the absence of a temperature gradient and demonstrate ultra-high thermal rectification in asymmetric trapezoid-shaped graphene. These unique properties have potential applications in power generation and thermal circuits, functioning as thermal diodes. Our findings also show the presence of negative and zero thermal conductivity in this system. The negative thermal conductivity could enable the design of a conductive heat machine that pumps heat from the cold side to the hot side without additional energy consumption, functioning as a 'full-free refrigerator'. Meanwhile, zero thermal conductivity paves the way for the development of high-efficiency thermoelectric devices. Simulations were performed in two scenarios: with hydrogenated edges and without them. To ensure the reliability of the results, Reactive Empirical Bond Order and Tersoff potentials were employed. Finally, we examined how the SHC and the temperature difference at which the heat current is zero depend on the sample length, system width, and system temperature.

Perspective on phase change composites in high-efficiency solar-thermal energy storage

To clarify future research directions, this study first analyzes the heat transfer process of solar-thermal conversion and then reviews solar-thermal phase change composites for high-efficiency harnessing solar energy. The focus is on enhancing heat absorption and conduction while aiming to suppress reflection, radiation, and convection. Most advancements have concentrated on improving absorption and thermal conductivity, while reducing the aforementioned unfavorable processes remains less explored. In the current research, the best results show that the solar-thermal conversion efficiency has approached the theoretical limit (100%), and a typical thermal conductivity has reached 33.5 W/(m·K). However, further enhancement of the absorption and conduction remains a challenge, highlighting the need for structural modifications and grafting. Other factors hindering conversion efficiency have received limited attention and warrant further in-depth investigation, with the potential to reduce reliance on fossil fuels and contribute to environmental sustainability.

Combined Flow and Temperature Nonuniformity in Compact Cross‐Flow Three‐Fluid Heat Exchangers

ABSTRACTCryogenic processes often involve the heat interaction of multiple fluids and are highly sensitive to even minor variations in operating conditions. Hence, flow and temperature nonuniformity adversely impact the performance of thermal systems, and their combined occurrence can be especially detrimental. The transient response and thermal effectivity of a cross‐flow three‐fluid heat exchanger are investigated while considering the flow and temperature nonuniformity at the inlet section. Four modes of combined flow and temperature nonuniformity are opted, which replicates the pragmatic situation existing in the working of heat exchangers, and the effectivity of the thermal system is evaluated by its alignment with the uniform flow mode. Flow nonuniformity is implicated in both the inlet section and within the core all along with the effect of fluid back mixing. The “Dankwert's” boundary condition is specifically used to account for the effects of axial dispersion within the fluids. The model incorporates longitudinal heat conduction in partition walls, with the “finite difference method” employed to solve the partial differential equations. To the best of our knowledge, the present study is the first attempt to analyze both the transient response and effectivity of three‐fluid heat exchangers under combined flow and temperature nonuniformity. It is learned that thermal effectivity is degraded by 31.5% and enhanced by 1% under flow nonuniformity mode QPQ and temperature nonuniformity mode 1 respectively. Under the combined mode of both, the effectivity settles down somewhere amid both and is found to be degraded by 8%. The higher NTU comes up with a sharp peak in temperature distribution, which makes the core more prone to cracks.

Experimental Investigation of Infrared Detection of Debonding in Concrete-Filled Steel Tubes via Cooling-Based Excitation

Debonding in concrete-filled steel tubes (CFSTs) is a common defect that often occurs during the construction phase of CFST structures, significantly reducing their load-bearing capacity. Current methods for detecting debonding in CFSTs using infrared thermography primarily rely on heat excitation. However, applying this method during the exothermic hydration phase presents considerable challenges. This paper proposes the innovative use of spray cooling as an excitation method during the exothermic hydration phase, providing quantitative insights into the heat conduction dynamics on steel plates for infrared debonding detection in CFSTs. The effects of atomization level, excitation distance, excitation duration, and water temperature in the tank on infrared debonding detection performance were examined. The timing of the maximum temperature difference under cooling excitation was analyzed, and the heat conduction characteristics on the surface of the steel plate during the cooling process were explored. A highly efficient and stable cooling excitation method, suitable for practical engineering detection, is proposed, providing a foundation for quantitative infrared debonding detection in CFSTs. This method does not require additional energy sources, features a simple excitation process, and results in a five-times increase in temperature difference in the debonded region after excitation.

Effect of keyhole and lack-of-fusion pores on the anisotropic microstructure and mechanical properties of PBF-LB/M-produced CuCrZr alloy

Abstract Due to the high reflectance and heat conductivity of copper and its alloys, the processing window for laser-based powder bed fusion (PBF-LB/M) processing of high-density copper components fundamentally overlaps with conduction and keyhole melting zones, resulting in the emergence of certain pores in the structure of printed parts. The present research aims to study how the development of process-induced lack-of-fusion or keyhole porosities during the PBF-LB/M process can affect the anisotropic microstructure and mechanical properties of the produced copper alloys. For this purpose, several samples were produced utilizing a similar CuCrZr-feedstock composition but varied process parameters from different areas of the PBF-LB/M processing window, specifically at laser powers of 300 W and 380 W which define the boarders of the conduction and keyhole regimes. X-ray computed tomography (XCT) revealed that the 300-W and 380-W samples achieved relative densities of 98.88% and 99.99%, respectively, with elongated lack-of-fusion pores forming at 300 W and semi-spherical keyhole pores at 380 W. Microstructural analyses employing scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) demonstrated strong anisotropy in different build directions of the samples, owing to the growth of long columnar grains with intense < 101 > orientation along the build directions. Here, the emergence of different types of pores can cause competition between the epitaxial growth of columnar grains and the heterogeneous nucleation of new grains on the layers’ interfaces, thereby significantly varying the grain size, preferred orientation, crystallographic texture, and microstructural anisotropy of the samples. Furthermore, compression tests and nanoindentation measurements of the printed alloys in the longitudinal and transverse directions revealed that the 300 W and 380 W samples exhibited compressive strength anisotropies of 0.061 and 0.072, and average nanoindentation hardness values of 1.3 GPa and 1.5 GPa, respectively. The orientation of elongated lack-of-fusion porosities perpendicular to the loading axis was identified as the most damaging factor, significantly reducing mechanical performance compared to the uniformly distributed keyhole pores.

Stabilization of a coupled bridge system with past history and gurtin-pipkin’s heat conduction

The asymptotic stability of the vertical vibrations of a suspension bridge and the main cables from which the bridge is suspended by the cables is investigated. The history of the materials of the bridge and the effect of heat governed by Gurtin-Pipkin’s thermal law on main cables are taking into consideration. We show that the damping induced by the infinite memory of the bridge and the heat on the main cables are strong enough to stabilize the system.

Thermohydraulic performance optimization of integrated porous pin fins in microchannel heat sink using shape optimization coupled with NSGA

Micro porous heat sink (MPHS) with enhanced heat transfer performance faces higher pressure drop challenges than conventional heat sinks. Practical applications of MPHS are recently investigated focusing on basic structures. But explorations on complex structures and their performance enhancement are limited. Moreover, the heat conductivity along channel height direction needs further enhancement. To address the problems and extend porous fin designs, we propose a brand-new bionic integrated porous pin fin in MPHS. Procedures of shape optimization coupled with NSGA are applied to the porous fin design. The objective is chosen as figure of merit (FOM) regarding integrated pin fin spacing, solid sub pin fin spacing, and porous zone diameter. This novel method in MPHS investigation helps to find the optimal geometric parameter combination and counter-intuitive design. Then, a detailed performance comparative analysis for the optimized structure is conducted. The results show improvement ratio ranges of FOM are 18.79–––21.65%, 71.84–––108.72%, and 212.7–––231.5%, compared to non-optimized, partially-filled, and fully-filled structures, respectively. This work indicates that the innovative design attains significant energy efficiency improvement, and the novel method is feasible for comprehensive optimization.

Research on the heat conduction, physical and rheological properties of asphalt binder modified with boron nitride

Research on the heat conduction, physical and rheological properties of asphalt binder modified with boron nitride

A novel model for the thermoelastic hydrodynamic lubrication characteristics of the slipper pair in radial piston pumps

Relying on heat conduction and thermoelastic mechanics theories and Takeuti's research, a novel TEHL (thermoelastic hydrodynamic lubrication) model considering thermal effect-induced thermoelastic deformation was developed. The impact of the radial piston pump's slipper pair's working and structural parameters on lubrication under heavy oscillating load was studied. The model was shown to be valid and superior in simulating oil film changes in TEHL, EHL (elastic hydrodynamic lubrication), and HL (hydrodynamic lubrication). It was first used to analyze how different conditions and parameters affect slipper pair lubrication. Thermoelastic deformation simulations were more accurate than previous elastic ones, making results more comprehensive. Friction experiments gave a coefficient of about 0.25 at 400–600 r/min and 0.23 at 600–1000 r/min, while the simulation result was 0.215. The HL model had a thin film, high temperature, and asymmetric pressure at x1 during suction, and increased thickness, decreased temperature, and uniform pressure at y1 during high pressure. In the HL model without deformations, the film was 12.9–14.0 μm thick and 345.7–354.0 K in temperature. In the EHL model with elastic deformation (0.6–2.6 μm), the thickness was 13.6–15.9 μm. In the TEHL model with thermoelastic deformation (0.5–2.1 μm), the thickness was 13.2–15.6 μm and the temperature was 344.4–354.0 K. Also, film thickness, speed, pressure, angle, radius, and ratio significantly affect slipper pair TEHL. This series of simulations proved the proposed model's feasibility for studying TEHL under heavy, variable loads and different structures. The model can optimize pump design parameters, boosting efficiency, and extending service life, and also enables fault prediction and prevention and maintenance strategy optimization, enhancing equipment reliability and production efficiency.

Thermal transport recovery in irradiated SiC mediated by nano-layered stacking faults

We investigate phonon thermal transport and resistance to ion irradiation in nanostructured 3C-SiC using molecular dynamics (MD) simulations. Two-dimensional planar defects in the form of stacking faults (SFs) spaced within nanometer-scale vicinity from each other promote healing of both: radiation-induced point defects (PDs) and thermal conductivity (k) under 10 keV Si ion irradiation number of displacements per atoms (DPA= 0.0016 – 0.034). With the rise of DPA below the onset of amorphization, the decay in k due to PDs and SFs is found to be less rapid than that due to the presence of only PDs. Observed relative recovery of heat conductivity is due to enhanced recombination of Frenkel pair PDs spatially confined between neighboring SFs, as confirmed by collision cascade MD simulations. Calculations from the Boltzmann transport equation combined with the Klemens model are consistent with findings from MD simulations. The interplay between enhanced PD recombination and thermal transport recovery is observed for different types of SFs. Obtained results pave the way to guide the design of nano-engineered nuclear ceramics with simultaneously enhanced radiation tolerance and heat conductive properties.

The Crucial Role of Geothermal Fluids in Reducing the Water and Carbon Footprints of Lithium Mining in Salt Flats Worldwide

ABSTRACT Thermal waters, which often have a high Li concentration, can influence the formation of Li-rich brines in the salt flats. Several studies suggest that geothermal activity accelerates the leaching of Li-rich volcanic rocks in the catchment areas of the closed basins, contributing to higher Li concentrations in brines. Considering that there is no salt flat in Chile or other parts of the world that does not have a present-day (active) or palaeo-geothermal system, there is a need for a holistic geoscientific study of the salt flats to investigate the association between lithium enrichment of brine in the salt flats and geothermal systems present in the host closed basins. The expected results of such studies in different salt flats will help understand the role of geothermal systems in forming economic Li deposits that could be selectively mined sustainably. This is because thermal waters can also concentrate Li in specific horizons, allowing for selective extraction with minimal impact on freshwater aquifers. This would be possible because conductive heating by underlying thermal water could induce circulation (convective overturn) of basin brines within hydrologically connected horizons. Accordingly, this geothermally induced brine circulation may develop a heterogeneous subsurface Li distribution, where thermal waters could be instrumental in forming Li-enriched horizons in subsurface brine. Deciphering and modeling the latter will form a strong and tangible basis for developing environmentfriendly methods for Li mining that will have negligible influence on the groundwater and wetland ecosystems using drilling technologies prevalent in the hydrocarbon industry for extracting particular sedimentary horizons. Further, geothermal systems present in the closed hydrologcal basins could aid in reducing the environmental footprint of Li mining by providing thermal energy for extraction processes and electricity generation using low-enthalpy binary power plants. Considering the focus on direct extraction of Li (DLE) in Chile and neighboring countries, it is necesary to integrate it with geothermal following holistic geoscientific studies involving geological, geochemical and geophysical investigations, validated by exploratory drilling. This will help mitigate environmental challenges associated with current DLE technologies by using geothermal water in the extraction process and expertise from the geothermal industry in brine recharge.

Moisture Induced Changes in Engineering, Thermal and Mechanical Properties of Custard Apple (Annona squamosa L.) Seeds

ABSTRACTPresent research has been carried out to study the physical, thermal and mechanical properties of custard apple seed. The analysis assessed the effect of moisture content (7.8% to 30% d.b.) on diverse engineering properties of custard apple seeds. It was found that as the amount of moisture increased, number of properties, including seed length (L), seed width (W), and seed thickness (T), increased linearly. The results indicated the surface area of seed (Sa), volume of seed (V), angle of repose (θ) and mass of thousand seed (M1000), increased from 199.46 to 218.89 mm2, 181.78 to 210.19 mm3, 17.3° to 31.5°, and 234.63 to 280.46 g, respectively, with an increase in moisture content. The true density (ρt), bulk density (ρb) and porosity increased 19.13%, 15.74%, and 2.2%, respectively as the moisture content increased. The static coefficient of friction (μ) increased as the amount of moisture increased for various surfaces, that is, glass, galvanized iron (GI), and stainless steel (SS) from 0.316 to 0.522, 0.311 to 0.614, and 0.289 to 0.438, respectively. Hardness and thermal property are the two novel characteristics that have been used for seed characterization. When the amount of moisture increased then texture property dropped. Thermal conductivity (λ) and specific heat per unit volume (ρcp) increased from 0.13 to 0.17 W m−1 K−1 and 0.51 to 0.73 MJ m−3 K−1 and thermal diffusivity (α) reduced from 0.25 to 0.18, as the amount of moisture of custard apple seed raised.