Radiative Heat Transfer Research Articles

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.

Galerkin finite element analysis on radiative heat transfer in titanium dioxide-polyalphaolefin nanolubricant past a convergent/divergent channel with non-uniform heat source/sink effect

The current study inspects the radiative heat and mass transport of a polyalphaolefin (PAO) – based nanolubricant flow consisting of titanium dioxide (TiO2) nanoparticles in a convergent/divergent channel with thermophoresis, Brownian motion, and non-uniform heat source/sink effects. The mathematical modelling of the present problem results in a system of complex non-linear partial differential equations (PDEs). The Galerkin finite element method (GFEM) is adopted to solve complex equations and to obtain the solution for the field variables in convergent/divergent channels. The results revealed that as the values of Brownian motion get higher, the temperature dispersal in the channel quickens, whereas the concentration profile slows down. The rise in the value of the thermophoresis parameter increases the thermophoresis force, which causes liquid particles to be dispersed in the stream. The heat transmission rate increases with an increase in radiation parameter values.

Numerical exploration of radiative heat transfers in a magneto bioconvection Maxwell fluid passing through a spinning disk

Numerical exploration of radiative heat transfers in a magneto bioconvection Maxwell fluid passing through a spinning disk

Study on analogy principle of overall cooling effectiveness for high temperature cooling structure considering thermal radiation heat transfer

With the continuous advancement of aero-engine technology, the performance of hot-end components such as combustion chambers and turbines has significantly improved, leading to a rapid increase in the working environment temperature surrounding these components and an increasingly prominent thermal radiation effect. Due to the non-gray body characteristics and spectral selectivity of thermal radiation, it is difficult to replicate the actual working environment of turbine components under laboratory conditions, causing many scholars to ignore or simplify the thermal radiation effect. Focusing on the overall cooling effectiveness of hot-end components such as turbine guide vanes, this paper proposes a method for modeling the overall cooling effectiveness of cooling structures under radiation-convection coupling conditions by matching parameters such as Burger number (Bu) and Boltzmann number (Bo). Based on the impingement effusion plate model and turbine guide vane model, this study investigates the matching of the overall cooling effectiveness under full coupled heat transfer for cooling structures in high and low operating conditions in laboratory settings. Additionally, the effects of momentum ratio, temperature ratio, and gas composition on the overall cooling effectiveness are examined. The results indicate that this matching method can provide important references for the design of hot-end components such as turbine blades.

Cross-sectional zero-dimension temperature model for thin-walled circular tubes in space environment

A sufficiently accurate, yet computationally efficient prediction of temperature field is essential for design of spacecraft structures. This paper presents a model dimension reduction method for thermal analysis of thin-walled circular tubes in space environment, which takes into account radiation heat transfer among the internal surfaces besides heat conduction along the circumferential direction and radiative emission from the external surface. Temperature distribution on the tube cross section is approximated by a series of harmonic functions, so that a one-dimensional problem is reduced to that of zero dimension. The relation between average and perturbation temperatures that depend only on time is broadened to fully coupled one. By comparison to the previous model and the plane finite element model, the accuracy and economy of the new model are illustrated. The results show that internal radiation exchange plays an important role in thermal analysis of thin-walled circular tubes used extensively in spacecraft appendages. Furthermore, differences between present and previous models are analyzed and a two-way analysis of variance is performed to determine the effect of various physical and geometric parameters on the temperature distribution and response of the tubes. The work can be further developed to analyze thermally induced deformation and vibration of spacecraft structures.

Simultaneous use of convection and radiation heat transfer for Iranian pistachio drying using catalytic heater - numerical and experimental study

This study presents a comprehensive investigation into the simultaneous use of convection and radiation heat transfer for Iranian pistachio drying using a catalytic heater. Both experimental and numerical analyses were conducted to evaluate the performance of the proposed system. The experimental setup involved a catalytic infrared heater, which provided a consistent temperature of approximately 370 K within the drying chamber. The results indicated that the drying time was reduced by 40% compared to traditional hot air drying methods, with an average moisture reduction rate of 0.8% per minute. The numerical analysis, conducted using computational fluid dynamics (CFD) simulations, supported the experimental findings, showing a uniform temperature distribution across the pistachios and efficient heat transfer. The catalytic heater demonstrated a combustion efficiency of 98%, with CO emissions below 10 ppm and zero NOx emissions, highlighting its environmental benefits. Overall, the combined experimental and numerical results confirmed that the proposed catalytic heater system not only enhances drying efficiency but also significantly reduces energy consumption and greenhouse gas emissions compared to conventional drying methods.

An experimental setup for studying conduction and radiation heat transfer in a rotary drum

This study presents the development of a novel heating system that aims to bridge the experimental gap for analyzing both radiation and conduction heat transfer in a rotary drum. The experiments were conducted by loading the drum with 4 mm silica glass beads at varying fill levels (10 %, 17.5 %, and 25 %) and rotation rates (2, 5, and 10 RPM), and monitoring the temperature evolution with an infrared camera. Higher fill levels resulted in lower average particle bed temperatures, while rotation rate influenced the contact time between particles and the drum wall and the exposure to radiative heat. A rotation rate of 5 RPM resulted in the highest average bed temperature due to optimal contact and exposure time for conduction and absorption of radiative heat, respectively. Thus, a balance between adequate particle mixing and optimal contact/exposure time is crucial for maximizing heat transfer efficiency in rotary drums exhibiting conduction and radiation.

Enhanced radiative heat transfer and modulation using VO2-based metasurfaces

Enhanced radiative heat transfer and modulation using VO2-based metasurfaces

Experimental study on internal heat transfer among adjacent rooms for building energy efficiency with housing vacancy consideration

With the expansion of the real estate sector and the rise of tourist resorts, many individuals now own multiple properties, resulting in a substantial number of homes remaining vacant for extended periods or being used seasonally. Despite being unheated, rooms in these vacant properties continue to transfer heat to adjacent heated rooms. While previous research has explored the heat transfer between non-heated and heated rooms based on their relative positioning, few studies have considered the dynamic aspects of this process. To fill this gap, we developed a scaled-down model to replicate real-world conditions and conducted experiments to track the dynamic temperature changes between non-heated and heated rooms in different configurations. The heat transfer mechanism was analyzed, and a theoretical model was constructed to quantify the dynamic heat exchange. This model accounts for variations in both convective and radiative heat transfer between rooms. Initial findings suggest that heat transfer to a non-heated room below a heated space can reach 28 % of the total heat supplied, while heat transfer to an upper adjacent room can account for 16 %. The peak heat transfer is observed after 5–10 h of heating. These results provide valuable insights for optimizing space heating, promoting energy-saving practices, and improving indoor heating efficiency, alongside offering actionable recommendations for behavioral energy conservation.