Radiative Heat Transfer Research Articles

Impacts of scattering of non-gray gas particulate mixtures on radiative heat transfer and mid-infrared image temperature in a 2D oxy-coal combustion furnace

Impacts of scattering of non-gray gas particulate mixtures on radiative heat transfer and mid-infrared image temperature in a 2D oxy-coal combustion furnace

Phase-transition metamaterial smart window for radiative cooling and privacy protection

This paper proposes a smart window for radiative cooling with adjustable transparency by leveraging the phase transition property of VO2. The proposed smart window exhibits daytime visible light transmission and near-infrared light reflection, all-day radiative cooling, and a nighttime privacy protection feature. It comprises a bottom layer of VO2/Ag/VO2 and top cubic two-dimensional SiO2 gratings, with structural parameters optimized by the genetic algorithm to ensure excellent optical performance. In the daytime, 75.4% visible light transmittance and 87.8% near-infrared reflectance can be achieved by utilizing the dielectric state of VO2. It also achieves low light transmission of 9.8% by using the metallic state of VO2, which is suitable for nighttime privacy protection. Furthermore, it has an all-day outside emissivity of 98.2% for radiative cooling, together with a low inside emissivity of 1.9% for effectively inhibiting the radiation heat transfer. In addition, the proposed structure is insensitive to the angles of incidence and the polarization of light, making it advantageous for radiative cooling. During the daytime, it reduces the temperature by 17.7 K compared to a glass of equal thickness when the non-radiative heat coefficient is 12 W/m2/K. At night, it achieves a cooling power of 124.7 W/m2, achieving a cooling effect of 8.9 K below ambient temperature. The proposed smart window is promising for various application scenarios for radiative cooling and privacy protection and could be used as windows for buildings and vehicles.

Boost heat transfer efficiency through thermal radiation and electrical conductivity in nanofluids

AbstractThermal radiation and electrical conductivity in nanofluids are crucial for their heat transfer characteristics, especially in applications with elevated temperatures or significant radiative heat transfer. The suspension of nanoparticles in suspension contributes to the fluid's electrical conductivity, which is essential for efficient heat dissipation in electronic cooling systems. Understanding the behavior of electroconductive nanofluids is particularly important in electronic cooling applications, where effective heat dissipation is crucial to prevent overheating. A study using a similarity parameter transformed a system of coupled PDEs into a set of nonlinear ordinary differential equations, revealing significant changes in key physical characteristics, such as temperature distribution, cubic concentration field, and velocity field. The study also examined the effects of parameters like Brownian motion, Rayleigh number, Peclet number, thermophoresis parameter, and buoyancy ratio parameter. The research provides valuable insights into the complex dynamics of magnetized non‐Newtonian nanofluids and offers practical implications for applications like microbial fuel cells and heat transmission equipment.

Radiative-conductive heat transfer dynamics in dissipative dispersive anisotropic media

Abstract We develop a self-consistent theoretical formalism to model the dynamics of heat transfer in dissipative, dispersive, anisotropic nanoscale media, such as metamaterials. We employ our envelope dyadic Green’s function method to solve Maxwell’s macroscopic equations for the propagation of fluctuating electromagnetic fields in these media. We assume that the photonic radiative heat transfer mechanism in these media is complemented by dynamic phononic mechanisms of heat storage and conduction, accounting for effects of local heat generation. By employing the Poynting theorem and the fluctuation-dissipation theorem, we derive novel closed-form expressions for the radiative heat flux and the coupling term of photonic and phononic subsystems, which contains the heating rate and the radiative heat power contributions. We apply our formalism to the paraxial heat transfer in uniaxial media and present relevant closed-form expressions. By considering a Gaussian transverse temperature profile, we also obtain and solve a system of integro-differential heat diffusion equations to model the paraxial heat transfer in uniaxial reciprocal media. By applying the developed analytical model to radiative-conductive heat tranfer in nanolayered media constructed by layers of silica and germanium, we compute the temperature profiles for the three first orders of expansion and the total temperature profile as well. The results of this research can be of interest in areas of science and technology related to thermophotovoltaics, energy harvesting, radiative cooling, and thermal management at micro- and nanoscale.

Analysis of Thermal Isotropy of Parallelepiped Shape of Bronze Samples for Mechanical Engineering Applications

Objective: The need to find out whether the specimens are ‘thermally thin’ or not is the basis for applying the law of conservation of energy or the Fourier differential equation of heat conduction in finding the time dependence of the specimen temperature. The aim of this study is to find out the thermal field distribution in a parallelepiped shaped bronze specimen and to verify the Bio number. Methods: A number of external variables make it difficult to maintain a monotonic change in sample temperature during the ‘heating’ stage. These factors led to the use of the cooling method to study tiny samples with low inertia of the thermal process. We used the cooling method to experimentally verify the isotropy of the thermal field in the sample and to study the kinetics of cooling relative to the sample axes over a wide range of temperatures. Results: It was found out that in natural air cooling the main mechanisms are conductive, convective and radiative heat transfer. The contribution of thermal radiation to the cooling process is noticeable at high temperatures. It was found that the typical cooling time increases with sequential radiative, conductive and convective heat transfer. By extending the temperature study area to, for the first time, we were able to observe each component of the heat transfer process independently. The values of the typical cooling time on all axes correspond to the experimental error bounds. It was found that the temperature value of the sample is independent of the coordinates and depends only on time. In this case, the law of conservation of energy can be used to explain the dependence of body temperature on cooling time. Conclusion: It is shown that the sample under study is ‘thermally thin’, i.e. the thermal field is constant in all directions. In this situation, the thermal balance equation should be applied rather than the Fourier differential equation of heat conduction, since the temperature gradient inside the body is practically zero. The results obtained are of great importance for the study of cooling processes of metallic products in thermal power engineering, heat engineering and thermophysics.

Radiative heat transfer to enhance the performance of liquid metal-based phase change heat sink under natural convection condition

Liquid metal phase change materials have the advantages of high thermal conductivity and high volumetric latent heat, which are expected to address the growing challenges of thermal management of advanced electronics. In previous studies, the effect of radiative heat transfer from fins of a phase change heat sink on thermal management performance has rarely been considered. In this study, radiative coating materials with high emissivity were prepared and coated on the fins of the liquid metal phase change heat sink. The effect of radiative heat transfer on the performance of liquid metal phase change heat sink was investigated. The experimental results of continuous heating under natural convection conditions show that the introduction of the radiative coating with an emissivity of 0.9298 can extend the time for the surface temperature of the heat source to reach 100 °C by 9.4%, while shortening the recovery time of the phase change heat sink by 14.9%. The results of high-power cyclic heating indicate that the high emissivity coating can reduce the peak temperature by 16.6 °C in the tenth working cycle. A simplified numerical model was subsequently developed and validated to determine the specific effects of phase change and radiative heat transfer on the overall thermal control performance. The radiation-enhanced liquid metal phase change heat sink proposed in this study is simple and maintenance-free. It is expected to address the thermal management issues of electronic devices that cannot use active cooling or operate in thin-air environments.

High-Quality Conductive Network Films Constructed from Carbon Nanotube/Carbon Nanofiber Composites via Electrospinning for Electrothermal Applications.

In this study, carbon nanotube (CNT)/carbon nanofiber (CNF) composite electrothermal films were prepared by electrospinning, and the effects of the CNT content and carbonization temperature on the electrothermal properties of the CNT/CNF composite films were investigated. The experimental results demonstrated that the conductivity of the CNT/CNF composite electrothermal film (0.006-6.89 S/cm) was directly affected by the CNT content and carbonization temperature. The electrothermal properties of the CNT/CNF positively correlated with the CNT content, carbonization temperature, and applied voltage. The surface temperature of CNT/CNF can be controlled within 30-260 °C, and continuously heated and cooled 100 times without any loss. The convective heat transfer with air is controllable between 0.008 and 31.75. The radiation heat transfer is controllable between 0.29 and 1.92. The prepared CNT/CNF exhibited a heat transfer efficiency of up to 94.5%, and melted a 1 cm thick ice layer within 3 min by thermal convection and radiation alone.

Air-cooling process modelling for cord steel based on fusion approach of mechanism and artificial neural network

In this study, a modelling approach is introduced that fuses the mechanistic model with an artificial neural network (ANN) during the cord steel manufacturing. This involves replacing certain mechanistic calculations with ANN representations, optimizing mechanistic parameters through ANN techniques, and implanting mechanistic equations into the ANN framework to achieve more accurate and efficient calculations of the cooling process. The mechanistic parameters come from the models including Natural Convection Heat Transfer, Forced Convection Heat Transfer, Radiation Heat Transfer and Phase Transition during the air-cooling process. The model demonstrated an average error of 8.6 °C and 5.4 °C, compared to measurement values from two temperature sensors on the air-cooling line, and an average error of 3.3 °C relative to manually obtained temperature.

Experimental and numerical investigation of heat transfer modes on pot surfaces in a power range of a cooking porous burner

The investigation of convective and radiative heat transfers to a cooking pot in a porous burner, coupled with an analysis of the pot's bottom and side contributions to total heat transfer, remains an underexplored area of research. In this study, we adopt a comprehensive approach, combining experimental measurements and 3D numerical models, to explore the practical application of a Silicon carbide porous burner fueled with natural gas in cooking pots with power ranging from 12.15 kW to 31.04 kW. Three primary aspects are examined: differentiating between radiative and convective heat transfer contributions, investigating porous mixing characteristics, and analyzing the burner's thermal and combustion efficiencies. To facilitate this investigation, a dedicated test bench is meticulously designed and constructed, equipped with state-of-the-art measuring instruments to effectively monitor the thermal behavior of the heating process. The results reveal that the higher Damköhler number at higher power, driven by the dominance of chemical time over mixing time, accentuates the importance of chemical reactions in heat transfer to the pot. Moreover, increasing the power leads to a reduction in the burner's overall thermal efficiency, from 29.2% to 18.8%, due to a higher energy waste percentage, escalating from 45.12% at P = 12.15 kW to 65.31% at P = 31.04 kW. This increase in power also strengthens the downward movement of the flame and its detachment from the pot surface. The pot's bottom contribution to total heat transfer ranged from 76.7% to 95.5%, with convection alone accounting for over 98% in all cases. Consequently, optimizing the pot bottom geometry for the purpose of enhancing convection presents promising avenues for significantly boosting thermal efficiency. These findings highlight the potential of the investigated porous burner for efficient and clean combustion in cooking appliances.

Experimental studies on the influence of smoke acceleration effect feedback to the flame behavior in the U shaped shaft of a high-rise building

This paper presents an experimental investigation of the feedback effect with smoke acceleration on flame behaviors in the U shaped shaft of a high-rise building. Heat release rate of the fire, depths and widths of the U shaped shaft are changed. The flame height, vertical maximum temperature in the open shaft and the heat flux distribution on the façade are studied. Results show that the flame height is elongated by the smoke acceleration effect in the U shaped shaft and larger than that in the open space. Correlations for the flame height are established by taking into account the geometries of the U shaped shaft. The vertical maximum temperature in the U shaped shaft first decreases rapidly then keeps room temperature, which are compared with that under stack effect in the staircase. The exponential decay law between the vertical maximum temperature and height is modified. The total heat flux is mainly affected by the width and heat release rate. Radiation heat transfer fraction is larger than 80 % in the continuous and intermittent flame regions, of which the flame emissivity is about 0.53.

Enhanced near-field radiative heat transfer between borophene sheets on different substrates

Abstract Near-field radiative heat transfer (NFRHT) has the potential to exceed the blackbody limit by several orders of magnitude, offering significant opportunities for energy harvesting. In this study, we have examined the NFRHT between two borophene sheets through the calculation of heat transfer coefficient (HTC). Due to the tunneling of evanescent waves, borophene sheet allows for enhanced heat flux and adjustable NFRHT by varying its electron density and electron relaxation time. Additionally, the near field coupling is further examined when the borophene is deposited on dielectric or lossy substrates. The maximum HTC is closely related to the real part of the dielectric substrate. As a case study, the HTC on the lossy substrate of MoO3, ZnSe and SiC are calculated for comparison. Our results indicate that MoO3 is the optimal substrate to get the enhanced energy transfer coefficient. It results in a remarkable value of 1737 times higher than the blackbody limit owing to the enhanced photon tunneling probability. Thus, our study reveals the effect of substrate on the HTC between borophene sheets and provides a theoretical guidance for the design of near-field thermal radiation devices.

A platinum-coated staggered reactor to intensify lean hydrogen/air combustion: A large eddy simulation study

Catalytic-aided combustion has been proven effective for premixed hydrogen/air mixtures, particularly under lean to ultra-lean conditions. However, minimising the required catalyst sets a significant challenge because noble metals with high catalytic activity are rare and expensive. Therefore, this study aims to intensify the catalytic combustion process by investigating a non-planar reactor comprising an array of platinum-coated half- and full-cylinders through large eddy simulation. A premixed mixture with a fuel-lean equivalence ratio of 0.15 and an incoming Reynolds number of 3500 based on hydraulic diameter is used. For comparison, a planar reactor without cylinders is also studied under the same operating conditions and with the same amount of platinum-coated surface area. The simulation employs the turbulent kinetic energy sub-grid model and the eddy dissipation concept to model the turbulent catalytic reacting flow. The discrete ordinate model is used to account for radiation heat transfer in the catalytic process. Numerical simulations are validated against experimental results prior to analysis. The findings indicate that the placement of cylinders along the reactor length enhances convective mass transfer and intensifies catalytic combustion, resulting in effective combustion over a smaller catalytic surface. Compared to planar models, non-planar reactors demonstrate a much better H2 conversion efficiency throughout the reactor length, saving nearly 62.5 % of the catalyst.

Integration of Local Wisdom of Natural Color Sasirangan in Project-based Learning with STEAM Approach to train Science Literacy

<span lang="EN-US">Science learning should provide meaningful experiences for students to understand various scientific phenomena in life. Integrating local wisdom in learning can improve scientific literacy because the various concepts learned are witnessed directly by students in life. This research uses theoretical studies to describe the integration of local wisdom of natural color sasirangan in project-based learning with the STEAM approach to improve science literacy.</span><span lang="EN-US"> The STEAM approach is in the form of a) science in the form of the phenomenon of abundant dye water from the pot due to expansion; b) technology in the form of sasirangan fabric dyeing machines; c) engineering in the form of manipulation of the use of natural dyes and fixation; d) art in the form of making sasirangan cloth motifs; e) Mathematics in the form of temperature measurement using a thermometer and heat to increase the temperature of the dye liquid. The stage of making sasirangan cloth consists of making patterns, jalujur, sisit, dye, dedel, washing and ironing. The concept of temperature and heat found in the process of making natural color sasirangan includes; a) the concept of temperature when cooked water slowly becomes hot; b) the concept of expansion on the phenomenon of natural dye water spilling from the pot when cooked; c) the concept of heat is seen in water that has a large mass requires more heat to achieve a certain temperature increase; d) The concept of radiant heat transfer can be proven when the sasirangan cloth is dried in the sun</span>

CFD Analysis of the Effects of a Barrier in a Hydrogen Refueling Station Mock-Up Facility during a Vapor Cloud Explosion Using the radXiFoam v2.0 Code

A CFD (computational fluid dynamics) analysis to investigate the effects of the installation of a barrier in a hydrogen refueling station (HRS) mock-up facility, with a dummy vehicle and dispensers in the vapor cloud region, during a hydrogen-air explosion using a gas mixture volume of 70.16 m3 was conducted to determine whether the radXiFoam v2.0 code with the established analysis methodology to predict the peak overpressure can be utilized to evaluate the safety of a HRS with such a barrier installed in a large city in the Republic of Korea. The radXiFoam v2.0 code was developed on the basis of the XiFoam solver in the open-source CFD software OpenFOAM-v2112 by modifying C++ source codes in several libraries and governing equations so as to ensure effective calculations of the hydrogen-air chemical reaction and radiative heat transfer through water vapor in a humid air environment and to remove unnecessary warning messages that arise when using the radXiFoam v1.0 code. First, we conducted a validation analysis on the basis of measured overpressure datasets from a near field to a far field of a vapor cloud explosion (VCE) site in the HRS mock-up facility to evaluate the uncertainty in prediction datasets by radXiFoam v2.0. After this validation analysis, we undertook CFD sensitivity calculations by installing barriers with heights of 2.1 m and 4.2 m at a horizontal distance of 2.3 m from the VCE region in the grid model used for the validation analysis to assess the effects of these barriers on reducing the peak overpressure of the blast wave. From these calculations, we judged that the radXiFoam v2.0 code can accurately simulate the effects of the barrier during a VCE, as the calculated overpressure reduction values according to the barrier height are reasonable on the basis of previous validation results from Stanford Research Institute’s explosion test with such a barrier. The results herein imply that the radXiFoam v2.0 code is feasible for use in HRS safety when barrier installation must meet the technical regulations of the Korea Gas Safety Corporation in a large city.

Enhancing Near-Field Radiative Heat Transfer between Dissimilar Dielectric Media by Coupling Surface Phonon Polaritons to Graphene’s Plasmons

Enhancing Near-Field Radiative Heat Transfer between Dissimilar Dielectric Media by Coupling Surface Phonon Polaritons to Graphene’s Plasmons

Crystal surface heat transfer during the growth of 300mm monocrystalline silicon by the Czochralski process

This paper investigated the lower heat transfer efficiency of ingot after increasing the size of Czochralski monocrystalline silicon. To improve the heat transfer efficiency, industrial Czochralski monocrystalline furnaces use water-cooling jackets to enhance crystal heat transfer. Through two-dimensional modeling, radiative heat transfer between monocrystalline silicon and the water-cooling jacket was investigated. The results showed that the effective radiation on the crystal surface decreased, then increased, and then decreased again. Numerical simulations showed that the maximum effective radiation on the surface was greater than 60 000 W/m2, which represents a significant increase in the heat flow density compared with the radiation of the crystal without using water cooling. According to the angle factor definition, a model of the radiative heat transfer angle factor between the water-cooling jacket and silicon rod was established. The dynamic correlation equation between the radiation angle factor and geometrical parameter of the hot zone, solidification rate, and solidification time was derived. Finally, a water-cooling jacket suitable for growing large monocrystalline silicon rod was designed according to the model, which improved the growth efficiency of the crystals. The results of the study are of great significance for optimizing water-cooling jackets.

Thermal Analysis of Infrared Heater as an Alternative Heat Source for Flexitank Application Using CFD

The heating pad was a mechanism for heating elements using steam as a heat source and heating the liquid inside a flexitank to liquidise for easy discharge completely. Alternative heat sources such as infrared, electric, and exothermic reactions may improve thermal performance for the heating process. Infrared heating is chosen for this study due to its efficient radiation heat transfer compared to conduction and convection. This study aims to determine the optimal infrared heater configuration to improve the time to liquidify fluid on the flexitank for easier discharge. Nine flexitank and infrared heater geometries were made using SolidWorks with different heater positions and heating element thicknesses. Each geometry was simulated using Ansys Mechanical to study the thermal performance of radiation heat transfer with three different heating element materials. The heat output and energy input obtained from the simulation were used to calculate heating time and energy efficiency, respectively. The effects of each parameter were studied to determine the best configuration of the infrared heater in terms of heating time, energy consumption and both. The results showed that the position of the heater plays the most crucial role in determining the heating time and energy consumption, as a heater position that produces a larger heated surface area on the flexitank can reduce heating time. The thickness of the heating element and its material contributes a minor impact on heating time and energy consumption. Increasing thickness would lower the heating time and increase energy efficiency if the thickness improves heat retention capabilities. Increasing material emissivity will increase the heating time. Higher conductive materials would use more energy compared to lower conductive materials. The heating time was improved by about 30% compared to a steam heating pad. Energy consumption was reduced by about 85% compared to a small steam generator. In conclusion, the infrared heater was a promising alternative as a heat source for flexitank applications.

Mechanisms of flame spread over convex polymethyl methacrylate building material

Polymethyl methacrylate (PMMA) is a widely used combustible building material in convex structures, such as highway sound barriers and building façades. However, most flame spread studies focus on flat surfaces. This study investigates flame spread along convex surfaces through a series of burning experiments with varying curvatures and widths. The average path flame spread rate increases along with a bigger curvature and width. By introducing a dimensionless average path flame spread rate, an empirical correlation linking the average path flame spread rate with sample width and curvature is proposed. In reality, flame spread over convex surface exhibits a distinct time-varying process. For a large curvature, the transition of the flame shape from a wall-fire regime to a pool-fire regime is observed during the process. Moreover, as curvature and width increase, the flame spread transitions from a two-stage process (regime I) to a three-stage process (regime II). In regime II, the transient flame spread rate initially decreases, then increases, and finally decreases again. This behavior is due to the shift from convection dominance to radiation dominance, although radiant heat transfer significantly influences regime I as well. During this transition, a two-peak phenomenon in radiant heat flux emerges, indicating the onset of regime II. Based on this phenomenon, a power-law correlation between curvature and sample width as the critical criterion for triggering regime II is determined. The results of this study have implications concerning the fire safety design of buildings.

Relationship between temperature gradient and growth rate during CZ silicon crystal growth

Temperature distribution in the growing crystal is the most important parameter that determines the grown-in-defects, growth rate, etc. There is a discussion either higher growth rate leads to larger thermal gradient or smaller thermal gradient. In this study, in order to make clear the reason of this discrepancy, the effects of growth rate on the shape of melt/crystal interface, and temperature distribution in growing crystal were investigated by numerical modeling. Firstly, as increasing the growth rate, the shape of melt/crystal interface becomes more concave. And temperature gradient along center axis on growing crystal increases as increasing the growth rate. On the other hand, temperature gradient along surface of growing crystal decreases as increasing the growth rate. To obtain higher growth rate, heat transfer should be enhanced. Along the center axis, heat transfer in vertical direction by heat conduction is dominant. Then concave interface shape and larger thermal gradient along center axis were obtained. In the periphery of grown crystal near the triple points, because of concave interface shape, heat transfer in radial direction, and radiative heat transfer from growing crystal become more important than heat transfer in vertical direction. Then smaller thermal gradient along the growing crystal surface was obtained. This surface temperature profile agrees well with Abe’s measurement results. It is cleared that higher growth rate leads to the higher heat transfer, and melt/crystal interface shape, and temperature distribution in growing crystal are determined by the balance of growth rate and heat transfer between heat conduction in vertical direction and heat conduction in radial direction combined with radiation heat transfer from crystal surface.

Conductive paths generation using topology optimization for worst-case thermal design in space systems

Designing thermal systems for space platforms is a challenging task due to the wide variability in thermal conditions during the orbit and the strict constraints imposed by other subsystems. Several strategies have been developed to address these challenges while minimizing the thermal control subsystem’s signature, encompassing different algorithms optimize components positions in the platform. When relocation is not possible, thermal couplings between components can be modified to enhance heat transfer and achieve more uniform temperature distribution. To design optimal thermal paths in 2D space structures, in this paper a topology optimization framework based on the Heaviside Projection Method is introduced, using the Lumped Parameter Method (LPM) and taking the radiation heat transfer into account. The algorithm’s performance is tested on a Printed Circuit Board (PCB) by designing an optimal copper layer to meet specific thermal requirements under both extreme hot and cold conditions. Results show a significant improvement in thermal compliance for all components with the addition of this high-conductivity layer. Additionally, a reduction method is introduced to transfer the material distribution from the optimization to a coarser mesh of any size, which is useful to facilitate its implementation in existing software, where a large number of degrees of freedom can be a limitation.