Heat Conduction Research Articles

Domain sampling methods for an inverse boundary value problem of the heat equation

Abstract We investigate the reconstruction of an unknown cavity inside a heat conductor with only single boundary measurement, which is a typical non-destructive testing of defects in material science using thermography. Mathematically, it can be formulated as an inverse boundary value problem for the heat equation. Two domain sampling methods, i.e., the range test (RT) and no-response test (NRT), are developed to realize the reconstruction. We first justify the convergence of the RT, which is based on the analytical extension property of solutions to the heat equation. Then we prove the duality of the RT and NRT by looking at the relation between their indicator functions. Consequently, the unknown cavity can be reconstructed by using either the RT or NRT if the solution associated to the single measurement cannot be analytically extended across its boundary. Next, we design two efficient algorithms for the RT and NRT to reconstruct the unknown cavity numerically. Each algorithm consists of two steps. The first step is to determine an approximation of the unknown cavity by implementing the sampling methods in a coarse grid, while the second step is to improve the reconstruction by using a fine grid in the approximate domain. The numerical results suggest that both algorithms can generate some rough information on the cavity with only one boundary measurement. Finally, by using this information as an initial guess for Newton's method, we improve the accuracy of the mentioned reconstruction results.

Experimental activities about heat conduction in metals

Abstract In this paper we describe two experimental activities regarding heat conduction in metals. The activities were designed according to the Predict-Observe-Explain strategy and are appropriate for primary and secondary school students. The aim is for the students to find out that heat is conducted at the same rate in all directions, regardless of the height difference from the heating point. The alternative idea attempted to be confronted through the aforementioned activities is that heat is considered a substance with fluid’s properties.

Estimation of Subsurface Structure Using Euler Deconvolution Method of Magnetic Data at the Geothermal Area of Sonai Village and its Surroundings, Konawe Regency

It has been carried out research with the aim of determining the subsurface structure at the geothermal area of Sonai Village and its surroundings, Konawe Regency. The data used are magnetic data obtained through field measurements at 126 points in the N180oS direction. After the data were subjected to diurnal and IGRF corrections, a residual (local) magnetic field anomaly of around -150 nT to 90 nT was obtained. On the residual magnetic anomaly map which has been reduced to the Pole (RTP), the Euler Deconvolution (ED) method is applied to the Index Structure N=0 to estimate the subsurface structure in the form of the presence of minor faults, and it is known that there are 5 minor faults at a depth of around 9 to 38 meters. Information on the existence of these faults is then used in 2D modeling. Modeling results show that these minor faults cut through two rock layers, which are the layers composed of conglomerate rocks from the Alangga Formation and peridotites as bedrock from the Ultramafic Complex. One of the minor faults closest to the manifestation area (hot spring) is at coordinates around 4o1’12.412” S and 122o7’24.263” E to 4o1’15.532” S and 122o7’19.561” E with a distance of ±15 meters. The existence of these minor faults is thought to be the migration routes for heat flow or conduction to the surface at the geothermal area of Sonai Village and its surroundings.

Thermodynamic and Kinetic Studies on the Pyrophoricity of Uranium Flakes

The objective of this work was to arrive at quantitative estimates of pyrophoricity of uranium in different geometries. The major source of heat generation was identified to be exothermic chemical reactions of uranium with moist air. Time evolution of temperature was studied for uranium considering 3D conduction and convection heat loss routes using Finite Element Analysis. Auto ignition temperature for uranium flakes was quantified using heat balance equation and was found to be around 500 K. Excess heat generation rates needed to cause auto ignition of uranium flakes at room temperature were also estimated. The major sources of excess heat leading to its ambient ignition could be attributed to friction and other exothermic chemical reactions of process impurities in uranium.

Investigation of the melting and solidification processes of a phase change material in cylindrical annular enclosures: A parametric study for energy densification in hot water tanks

The present study focuses on the analysis of the effect of the phase change material (PCM) cavity size on the melting and solidification processes for application to thermal energy densification in a hot water tank through latent heat thermal energy storage in cylindrical annular cavities. A 2D axisymmetric composite geometrical pattern is considered, formed by a phase change material surrounded by a conductive and an insulating material. A parametric study is conducted on the phase change material cavity size, and the results are presented using non-dimensional numbers: Fourier number, Rayleigh number, and aspect ratio. Two approaches have been developed based on local and global analyses. The local one showed the predominance of the conductive or convective heat transfer process concerning the influence of the phase change material size, and thus the Rayleigh number, on the evolution of the solid/liquid interface and streamline shapes. The global one allowed correlations for melting and solidification Fourier numbers with respect to the Rayleigh number and aspect ratio to be built from simulation data. Two parameters for each process have been identified and defined from the present study: the critical Fourier number and the aspect ratio constant. The critical Fourier number corresponds to the maximum Fourier number that the phase change material needs to achieve for a melting or solidification process. The aspect ratio constant provides information on the phase change material aspect ratio value where the Rayleigh number no longer influences the process. In the case of the melting process, this parameter is an indication that convection has reached a maximum intensity and no longer influences the process. Finally, this study proposes a suitable aspect ratio for optimizing the melting process: 19.32, and another for optimizing the solidification process: 16.29.

Use of Modified Organic and Inorganic Phase Change Materials for the Development of Personal Cooling Device

The human body needs comfort in every condition. Human health is significantly impacted by heat. The ambient air temperature rises in hot weather, which causes the human body to become fatigued and exhausted. Phase Change Materials (PCM) can solve this problem with high latent heat absorption values and a wide range of phase change temperatures. The objective is to develop a PCM-based cooling device that is safe, readily available, and easy to use in normal routine life. A personal cooling system, such as a cooling vest using PCM, can assist in preventing heat-related issues. In this study, Polyethylene Glycol-600 (PEG-600) and modified glauber salt are selected as thermal energy storage materials with melting temperatures of 18–22°C and 27°C, respectively. Graphene Oxide (GO) nanoparticles were synthesised and mixed into the PEG-600 to enhance its thermal conductivity and latent heat of fusion. GO nanoparticles were prepared by Modified Hummer’s method (MHM) and characterised by Fourier’s Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The latent heats and melting ranges of GO/PEG-600 and modified glauber salt were investigated by Differential Scanning Calorimetry (DSC). The addition of 0.6 wt.% GO to PEG-600 results in an increase in thermal conductivity of 6.1% and latent heat of 8%. The PCMs are encapsulated in aluminium packs, sealed, and kept in a cooling device. The developed cooling vest provides cooling for up to 95 minutes. The cooling vest is recharged by keeping it below 10°C for 20 minutes. The developed personal cooling device provides a passive, inexpensive, and safe cooling system by extracting heat from the human body.

Deep thermal state on the southern margin of the Zhangzhou Basin based on the electrical conductivity model

Exploring the internal spatial and thermal structure of the Zhangzhou Basin is of great scientific significance in understanding the properties of the deep heat sources and the heating mechanism of hot springs in this region. This study estimates the temperature distribution within the upper mantle of the Basin's southern margin using the Arrhenius equation and Hashin-Shtrikman bounds based on a two-dimensional crust-mantle electrical resistivity model. We also employ a layered simulation technique to calculate the crustal temperature distribution using a one-dimensional steady-state heat conduction equation, constrained by the upper mantle's top and ground surface temperatures. This approach displays the characteristics of the longitudinal variations and horizontal inhomogeneities in crust-mantle temperature. Additionally, we estimate the heat flow values within the study area. Our findings reveal that: (i) the upper mantle (at depths of 30 - 50 km) exhibits a temperature range of 700 - 1100 °C, with the presence of local Moho and upper mantle uplifts; (ii) the crustal temperature spans from 21 - 900 °C, with a diminishing influence of the upper mantle uplift area on crustal temperature at shallower depths; (iii) the surface heat flow values derived from our simulations range between 87 and 100 mW/m2, averaging at 93.23 mW/m2; (iv) the exploration of dry heat rock in this region is likely to reach a depth of at least 6 km. These results suggest that the genesis of hot springs in the study area is not solely influenced by the heat energy extracted from large-area granitic surrounding rocks during a long transport process, but is also considerably affected by local deep thermal anomalous bodies and deep-large faults.

A localized collocation method based on nonsingular fundamental solutions for steady-state heat conduction analysis in heterogeneous materials

A localized collocation method based on nonsingular fundamental solutions for steady-state heat conduction analysis in heterogeneous materials

Optimizing Syngas Production from Municipal Solid Waste Gasification: A Dual Reactor Fluidized Bed Study with Steam and CO2 as Gasification Agents

The escalating production of municipal solid waste (MSW) poses significant environmental and health hazards due to air, water, and soil pollution. Utilizing MSW as an energy source through gasification offers a promising solution to mitigate these impacts. This study investigates the gasification of MSW using a Dual Reactor Fluidized Bed, a thermal technology that converts solid substrates into usable gaseous fuels. The primary objective is to optimize the quality of the produced syngas by employing specific gasification agents, namely steam and CO2, and their mixtures. The research examines the effect of these agents on H2/CO ratios across a wide range of low operating temperatures, from 400°C to 700°C, using silica sand as a heat conduction medium between interconnected combustion and gasification reactors. The results demonstrate that the composition of syngas is strongly influenced by gasification temperature fluctuations. Increasing temperatures from 400°C to 700°C correlate with higher concentrations of CO and H2 in the syngas. The use of steam as a gasification agent yields H2 concentrations up to 25%, while transitioning from steam to CO2 leads to a substantial increase in CO composition, reaching 22.73%. Further analysis reveals that the H2/CO ratio decreases from 1,78 with steam and 0.64 with CO2, highlighting the crucial role of gasification agents in syngas quality. This study underscores the potential for optimizing syngas production from MSW by manipulating gasification temperatures and transitioning between different agents (steam, CO2, and their mixtures), resulting in an overall increase in the calorific value of the produced gas. These findings emphasize the opportunity to transform substantial environmental challenges associated with MSW into promising sustainable energy solutions through advanced gasification technologies.

Effect of electrically aligned polycrystalline diamond flakes on the through-plane thermal conductivity of heat conduction sheets

Heat conduction sheets, which are composed of a thermally conductive filler and a base elastomer matrix, are important for dissipating heat from devices to a heat sink. Alignment of the heat-conducting two-dimensional filler particles enhances the thermal conductivity of the heat conduction sheet. In this study, we prepared polycrystalline diamond (PCD) flakes and then electrically aligned the PCD flakes in the through-plane direction of heat conduction sheet samples. The PCD flakes were fabricated by pulverizing a synthesized PCD thin layer. The typical size of the PCD flakes was ∼1 μm in thickness and ∼35 μm in diameter. The PCD flakes were electrically aligned in a polydimethylsiloxane (PDMS) matrix by applying alternating high voltage with parallel-plate electrodes. The heat conduction sheet containing 20 wt% aligned PCD flakes in the matrix exhibited high through-plane thermal conductivity of 0.47 W m−1 K−1, while that of the heat conduction sheet with aligned granular diamond filler particles was 0.37 W m−1 K−1. The high thermal conductivity comes from the formation of a large contact area between the filler particles and flake network by electrical alignment in the heat conduction sheet.

Exploring the intermittency of magnetohydrodynamic turbulence by synchrotron polarization radiation

Context. Magnetohydrodynamic (MHD) turbulence plays a critical role in many key astrophysical processes, such as star formation, acceleration of cosmic rays, and heat conduction. However, its properties are still poorly understood. Aims. In this work, we explore how to extract the intermittency of compressible MHD turbulence from synthetic and real observations. Methods. We used three statistical methods, namely the probability distribution function, kurtosis, and scaling exponent of the multi-order structure function, to reveal the intermittency of MHD turbulence. Results. Our numerical results demonstrate that: (1) the synchrotron polarization intensity statistics can be used to probe the intermittency of magnetic turbulence, by which we can distinguish different turbulence regimes; (2) the intermittency of MHD turbulence is dominated by the slow mode in the sub-Alfvénic turbulence regime; and (3) the Galactic interstellar medium (ISM) in the low latitude region corresponds to the sub-Alfvénic and supersonic turbulence regime. Conclusions.We have successfully measured the intermittency of the Galactic ISM from synthetic and realistic observations.

Honeycomb-like Microthermal Traps on a Photothermal Surface for Highly Efficient Solar Evaporation.

Solar evaporation is an ecofriendly and practical method for seawater desalination. The photothermal layer, which absorbs solar energy and converts it to thermal energy, plays a crucial role in enhancing the efficiency of the evaporator. However, structural design methods for photothermal layers are often complex and energy-intensive. This work reports a simple and efficient strategy for fabricating a necklace-like beaded nanofiber self-organized honeycomb-structured photothermal material. The honeycomb-like cavities form numerous microscale thermal traps, achieving thermal localization while maintaining high energy utilization efficiency, which not only increases light absorption but also facilitates the diffusion and escape of steam. Besides, the hydrophobic honeycomb layer separates the photothermal layer and the interface water, which reduces considerable heat conduction loss and achieves an effective antisalting performance. These functional features endow the evaporator with an evaporation efficiency of 92.9%, and the evaporation rate reaches 2.11 kg m-2 h-1 at 1 sun irradiance, demonstrating its great potential for practical solar-driven seawater desalination under natural sunlight.

Electro-thermal dynamics in superconducting generators: An In-Depth investigation of AC losses and cooling techniques for a 10 MW rotor coil system

In the pursuit of optimizing superconducting generator systems, a comprehensive understanding of their electro-thermal behaviors is crucial. This study builds upon previous research on an 8-pole, 10 MW superconducting generator by Inanir et al. (2022, Journal of Superconductivity and Novel Magnetism, 35(11), 3189) and focuses on an in-depth electro-thermal analysis of the rotor coil system. The emphasis is on assessing the AC losses experienced during transitory current changes. By simultaneously solving Ampere's equation and the heat conduction equation under specific boundary conditions, the research provides a detailed insight into the interaction between electrical and thermal dynamics within the rotor coils. The paper highlights the importance of temperature dynamics in various cooling and current conditions. The results demonstrate that achieving an optimal balance in cooling, particularly with the use of liquid nitrogen, is critical for efficient operation. This study not only advances the understanding of superconducting generators but also highlights potential strategies for improving their reliability and efficiency.

Numerical computations of MHD mixed convection flow of Bingham fluid in a porous square chamber with a wavy cylinder

This work examines the behavior of Bingham fluids in porous media under magnetohydrodynamic (MHD) conditions, addressing a significant issue in fluid dynamics and heat transport. The authors study mixed convection in a porous square chamber with twisted cylinders using COMSOL Multiphysics and finite element techniques. Compared to other research, this one offers a more complicated and realistic model since it integrates Bingham fluid flow and MHD effects in a porous chamber with wavy cylinders. Plotting of streamlines, isotherms, and Nusselt numbers is done for several parameters: Numbers Reynolds (1, 5, 10, 50), Hartmann (0, 25, 50, 100), Bingham (0, 1, 5, 10), Darcy (10−4, 10−3, 10−2, 10−1), and Grashof (102,103,104,105) are among those assigned numbers. According to findings, larger Bn values promote thermal stratification and decrease flow mobility, which results in dominating conductive heat transmission. The nusselt number falls with Ha and Bn but rises with Re, Da, and Gr. The study aims to provide useful insights into several industrial disciplines, such as nuclear power plant architecture and petroleum engineering, by enhancing heat transfer in non-Newtonian fluids under magnetic fields. It also boosts the efficiency of chemical reactors and filters. Based on our findings, for lower Re = 1, the lowest value of Numean is 2.602, while at Re = 50, its values rise to 6.425.

Phonon polariton-mediated heat conduction: Perspectives from recent progress

AbstractIt has been well-accepted that heat conduction in solids is mainly mediated by electrons and phonons. Recently, there has been a strong emerging interest in the contribution of various polaritons, quasi-particles resulting from the coupling between electromagnetic waves and different excitations in solids, to heat conduction. Traditionally, the polaritonic effect on conduction has been largely neglected because of the low number density of polaritons. However, it has been recently predicted and experimentally confirmed that polaritons could play significant roles in heat conduction in polar nanostructures. Since the transport characteristics of polaritons are very different from those of electrons and phonons, polariton-mediated heat conduction provides new opportunities for manipulating heat flow in solid-state devices for more efficient heat dissipation or energy conversion. In view of the rapid growth of polariton-mediated heat conduction, especially by phonon polaritons, here we review the recent progress in this field and provide perspectives for challenges and opportunities. Graphical abstract

Quantitative analysis of the impact of room temperature stability on cryostat performance

The constant temperature in laboratories is crucial for precise low-temperature measurements. Currently, there are no reports on the specific temperature needs for such experiments or quantitative analyses of how room temperature fluctuations affect cryostat control. This paper proposes a method to quantitatively analyze these fluctuations and their impact on cryostat temperature control. Taking the cryostat using for 2 K-5 K thermodynamic temperature measurement as the research object, and conducts model simulation and experimental validation. The research results indicate the primary influence on the sphere’s temperature is the time-dependent fluctuation of the room temperature. As temperature fluctuations propagate from the cryostat’s outer casing to the sphere, heat conduction is the dominant factor. The temperature fluctuations inside the system caused by environmental temperature fluctuations can be quantitatively expressed by a simple linear formula, with the coefficient being the fluctuation attenuation rate, which is 6.590 × 10-4 in this system. The deviation between experimental results and simulation results is within 5 %. To keep the sphere’s ambient temperature influence below 0.077mK, or 20 % of cryocooler-induced fluctuations, the room temperature must be controlled within 0.12 °C. In addition, the fluctuation period of room temperature is controlled below 1 h, the 0th flange is thickened, the rod is lengthened, and the material of the rod is changed to G10 above 4.2 K and stainless steel below 4.2 K can also effectively attenuate the influence on system temperature control.

Energy conversion and transport in molecular-scale junctions

Molecular-scale junctions (MSJs) have been considered the ideal testbed for probing physical and chemical processes at the molecular scale. Due to nanometric confinement, charge and energy transport in MSJs are governed by quantum mechanically dictated energy profiles, which can be tuned chemically or physically with atomic precision, offering rich possibilities beyond conventional semiconductor devices. While charge transport in MSJs has been extensively studied over the past two decades, understanding energy conversion and transport in MSJs has only become experimentally attainable in recent years. As demonstrated recently, by tuning the quantum interplay between the electrodes, the molecular core, and the contact interfaces, energy processes can be manipulated to achieve desired functionalities, opening new avenues for molecular electronics, energy harvesting, and sensing applications. This Review provides a comprehensive overview and critical analysis of various forms of energy conversion and transport processes in MSJs and their associated applications. We elaborate on energy-related processes mediated by the interaction between the core molecular structure in MSJs and different external stimuli, such as light, heat, electric field, magnetic field, force, and other environmental cues. Key topics covered include photovoltaics, electroluminescence, thermoelectricity, heat conduction, catalysis, spin-mediated phenomena, and vibrational effects. The review concludes with a discussion of existing challenges and future opportunities, aiming to facilitate in-depth future investigation of promising experimental platforms, molecular design principles, control strategies, and new application scenarios.

Ballistic transport enhanced heat convection at nanoscale hotspots

Along with device miniaturization, severe heat accumulation at unexpected nanoscale hotspots attracts wide attentions and urges efficient thermal management. Heat convection is one of the important heat dissipating paths at nanoscale hotspots but its mechanism is still unclear. Here shows the first experimental investigation of the convective heat transfer coefficient at size-controllable nanoscale hotspots. A specially designed structure of a single-layer graphene supported by gold-nanorod array is proposed, in which the gold nanorods generate hundreds of nanometers heating sources under laser irradiation and the graphene layer works as a temperature probe in Raman thermometry. The determined convective heat transfer coefficient (1928+155 −147 W m−2 K−1 for the 330 nm hotspot and 1793+157 −159 W m−2 K−1 for the 240 nm hotspot) is about three orders of magnitude higher than that of nature convection, when the simultaneous interfacial heat conduction and radiation are carefully evaluated. Heat convection, thus, accounts to more than half of the total energy transferred across the graphene/gold nanorods interface. Both the plasmon induced nanoscale hotspots and ballistic convection of air molecules contribute to the enhanced heat convection. This work reveals the importance of heat convection at nanoscale hotspots to the accurate thermal design of miniaturized electronics and further offers a new way to evaluate the convective heat transfer coefficient at nanoscale hotspots.

Enhancing orthogonal finishing machining of Ti6Al4V with laser-ablated tool geometry modifications

Finishing machining of Ti6Al4V, known for its high strength and heat conduction resistance, demands optimisation to achieve high-quality end products. This study explores modifying the chip contact length on the rake face and altering the flank face with a cavity to minimise process forces and temperatures while maintaining cutting edge integrity. The research validates the manufacturability of ultra-short pulsed laser-ablated tool geometry modifications, indicating potential for industrial scale-up. Extensive experimental evaluations under dry conditions assess the impact of tool modifications at various feed rates for planing and turning. Significant reductions in process forces and temperatures were observed with rake face modifications, particularly at a cavity distance of approximately 34 µm. Ideal performance was noted for feed rates between 0.035 and 0.045 mm for planing and 0.040 to 0.045 mm/rev for turning. Smoothed Particle Hydrodynamics (SPH) simulations employing a Johnson-Cook material model were used to analyse chip formation and to predict the process forces. These simulations revealed a clear change in the chip formation and lower process forces and temperatures. The SPH results closely matched experimental outcomes, with a discrepancy of less than 7 % in cutting forces for both tool types, although feed forces were underestimated by about 50 %. The effect of the tool modification is reflected accurately at the respective feeds.

Size effect modellings of axial compressive failure of RC columns at low temperatures

This paper applied a thermal-mechanical sequential coupled mesoscopic simulation method to explore the axial compression performance and the corresponding size effect of Reinforced Concrete Columns confined by Stirrups (i.e., RCCS) at low temperatures, with considering the interaction between concrete meso-components and steel bars as well as the low-temperature effect of mechanical parameters. Based on the heat conduction analysis, the axial compression mechanical failure behavior of RCCS with four structural sizes (i.e., 267 × 267 × 801, 400 × 400 × 1200, 600 × 600 × 1800 and 800 × 800 × 2400 mm) and two stirrup ratios (i.e., 1.26% and 2.89%) at different temperatures (i.e., T = 20, −30, −60 and −90°C) was subsequently simulated. The effects of temperature, structural size and volume stirrup ratio on axial compression properties were quantitatively discussed. The results showed that the peak strength of RCCS increased with the decreasing temperature, and the smaller-sized RCCS showed a stronger effect of low-temperature enhancement. Both the residual strength and displacement ductility coefficient decreased with the decreasing temperature. The peak strength, residual strength and displacement ductility coefficient of RCCS decreased with the increasing structural size, showing obvious size effects. The size effect on peak strength increased with the decreasing temperature, (the maximum increase was nearly 140%), but the size effect on displacement ductility coefficient decreased (the maximum decrease was nearly 70%). The peak strength, residual strength and ductility were enhanced with the increasing volume stirrup ratio, which was helpful to reduce the influence of size effect. Finally, an improved size effect theoretical model was proposed, which can effectively predict the axial compressive strength of RCCS with different structural sizes and stirrup ratios at room and low temperatures. The present research results can provide reference for the large-scale engineering application of RCCS in low-temperature environments.