Radiative Heat Transfer Research Articles

Thermo-Mechanical Analysis of Masonry Brick Walls with Embedded Test Specimen Under Fire Exposure

AbstractThe present study is dealing with the heat transfer and deformation of masonry brick walls and an embedded fire safety steel door as well as their mechanical interaction when they were exposed to fire. A numerical approach based on the finite element method was applied to predict the temperatures and deformation. The heat transfer analysis of the wall considered the heat conduction and the radiative heat transfer within the voids of the brick. It was found that the thermal analysis predicted the temperature in the wall with high accuracy. The thermal analysis of the door was limited to the heat conduction and the water vapour transport within the door was neglected. However, the calculated temperatures were found to be reasonable and were further used for the structural analysis. When the door was placed in a central position in the wall, the predicted deformation of the wall was in close accordance to the measured data. The analysis of the door deformation showed that the pressure level and its time-dependency inside the steel door is a crucial factor for the simulation’s accuracy. When the door was placed in an asymmetric position, the wall deformation was increasing significantly. This phenomenon was also covered by the simulation, when the stiffness of the wall boundary condition was decreased. Although the numerical model was capable to calculate the deformation during the fire exposure, further research on the pressure inside the door and the mechanical conditions of the wall at the boundaries has to be done.

Thermally radiative nanofluid heat transfer analysis inside a closed chamber with gyrotactic microorganisms

Thermally radiative nanofluid heat transfer analysis inside a closed chamber with gyrotactic microorganisms

Surface plasmon-coupled radiative heat transfer between graphene-covered magnetic Weyl semimetals

Surface plasmon-coupled radiative heat transfer between graphene-covered magnetic Weyl semimetals

Integrated neural network based simulation of thermo solutal radiative double-diffusive convection of ternary hybrid nanofluid flow in an inclined annulus with thermophoretic particle deposition

Numerical simulation of magnetohydrodynamic radiative double-diffusive convective heat and mass transfer of a ternary hybrid nanofluid with thermophoretic particle deposition in an inclined annulus is studied. Both sides of cylinders are preserved at uniform temperatures, while the remaining sides are thermally insulated. The coupled nonlinear partial differential equations are solved using a finite difference approach. The detailed computational results of heat and mass transfer rate, temperature, concentration and flow fields are presented and discussed for a distinct range of significant physical parameters. The results demonstrated that increasing the angle of the inclination factor increases fluid flow. In light of buoyancy, when the annular cavity is set downward, the enhanced shear velocity is transported upwards, where it reaches its optimal temperature. The higher temperature difference leads to augmented dynamic fluid motion, particularly in the radial direction, as the system seeks to balance the thermal energy through convective transfer. The Brownian motion parameter has abrupt mobility of nanoparticles in liquid, which promotes particle collisions with liquid molecules, yielding kinetic energy. Increased values of thermophoretic parameters augment the thermophoresis force. Thermophoretic particle deposition increases the concentration of nanoparticles in an annulus due to the migration of particles from hot to cold regions under the influence of temperature gradient. The heat and mass transfer characteristics of ternary hybrid nanofluid are forecasted through an artificial neural network-based Levenberg–Marquardt backpropagated algorithm. The built model shows the heat and mass transfer rate root mean squared values through the Levenberg–Marquardt algorithm as one and mean squared error values as 1e-07 and 1e-08 respectively.

Effects of cross-sectional shape on the low observability of double serpentine nozzles

When unmanned combat aerial vehicles (UCAVs) egress from the battlefield after attacking the target, the defensive radar systems detect signals reflected by the cavity structure of the nozzle and engine of the UCAVs, threatening their survivability. Infrared (IR) guided missiles can also threaten them by detecting the gaseous plume and hot engine parts. We present a comprehensive investigation of the effects of the cross-sectional shape of double serpentine nozzles on thrust, IR signature, and radar cross section (RCS), which are associated with propulsive performance and low observability. The fillet radius and cross-sectional shape of the nozzles were considered as the main design variables. The thermal flow field was analyzed using the compressible Navier-Stokes equations, while the IR signature was analyzed with the radiative heat transfer equation with a narrow band model. The RCS was calculated using a multi-level fast multipole method of full Maxwell's equations instead of the approximate methods often employed. The double serpentine (DS) nozzle with an elliptical cross-section showed high pressure recovery and a 9.66 % lower IR signature than the DS nozzle with a rectangular cross section. The maximum RCS and mean RCS were lowest for the DS nozzle with an elliptical cross section, with a maximum difference in maximum RCS of 383 % and mean RCS of 90 % compared with the DS nozzle with a rectangular cross section. The DS nozzle with an elliptical cross section distributes the current more evenly across the central part of the engine than the DS nozzle with a rectangular cross section. The DS nozzle with an elliptical cross-section showed excellent nozzle performance with a negligible difference in thrust. In addition, the results show that the cross-sectional shape of the nozzles has different levels of impact on thrust and pressure recovery (negligible), IR signature (limited), and RCS (significant).

Modulation of radiative heat transfer by higher-order topological phonon polaritons

Modulation of radiative heat transfer by higher-order topological phonon polaritons

Highly efficient spectrum-splitting solar energy utilization based on near- and far-field thermophotovoltaics

Improving the efficiency of solar energy utilization systems is of great importance in solar energy utilization. Near-field thermophotovoltaic cells can achieve a high power density and, therefore, efficiently utilize radiative heat transfer. An efficient spectrum-splitting solar energy utilization system based on near- and far-field thermophotovoltaics was proposed. The input solar energy was divided by the splitter, and the two parts of the energy were utilized differently. The concentration ratio can determine the energy input of the system, which can affect the photoelectric conversion efficiency of the system. Further, the vacuum distance can modulate the near-field radiative heat transfer, thus significantly impacting system performance. Based on the fluctuation dissipation theorem and Maxwell's equations, a system model was constructed and calculated using the optimal design method, and the effects of these parameters were investigated. Moreover, the optimal efficiency was obtained under different operating conditions. The optimal cascade system efficiency reached 39.93 % at a concentration ratio of 3000, which was 15.59 % higher than that of a single photovoltaic system. Thus, this study proposes a method for the efficient utilization of solar energy. In addition, it provides guidance for the subsequent design and construction of spectrum-splitting cascade systems based on near- and far-field thermophotovoltaics.

Detailed radiation modeling of two flames relevant to fire simulation using Photon Monte Carlo — Line by Line radiation model

This work reports benchmark data sets for radiative heat transfer in two distinct fire configurations obtained from the Measurement and Computation of Fire Phenomena (MaCFP) working group database. The cases include a 19.2 kW non-sooting turbulent methanol pool fire and a 15 kW sooting ethylene flame (referred to as the FM burner). The base configurations were simulated with large eddy simulation (LES) approaches using two different codes, namely FireFOAM and Fire Dynamics Simulator, respectively. Multiple frozen snapshots from these LES runs were radiatively evaluated using a photon Monte Carlo radiation solver and a line-by-line spectral model. The results were presented at three levels: Firstly, the radiative fields, including radiative emission, reabsorption, and heat flux contours, were shown. Secondly, the global radiative contributions from molecular gas species, soot, and wall boundaries were compared. Thirdly, a detailed spectral analysis of radiative fields for different components within five distinct spectral bands was presented. In the case of the non-sooting methanol pool fire, the radiative emission from CO2 predominates. However, for the radiation reaching the boundaries, both CO2 and H2O contribute almost equally. Conversely, for the sooty FM burner configuration, radiative emission from soot, CO2, and H2O all contribute similarly. In terms of radiation reaching the boundary, soot is the primary contributor in FM Burner. In the methanol pool fire, the pool surface receives a comparable contribution from CO2, H2O, and burner rim radiation, whereas, for the FM burner, the burner inlet surface primarily receives radiation from soot.

Forecasting the flame geometry and ground received radiative heat fluxes of two parallel adjacent fires of hydrocarbon fuel with crosswinds

Radiative heat transfer in fires is a critical parameter and a key aspect of gas storage and fire prevention design. In this study, the flame geometric scale characteristics and ground-received radiative heat fluxes from two parallel adjacent hydrocarbon fuel fires with crosswinds were examined. The separation distance between the two parallel flames, crosswind speed, and heat release rates were considered. The experimental results indicated that the flame tilt angle of the two parallel flames increased with increasing crosswinds. The horizontal flame length scale of the two adjacent parallel flames first increased with the crosswind until a critical point was reached, followed by a fluctuation with a further increase in the wind speed. To further quantify this flame phenomenon, a physical model of the flame interaction between two parallel fires under the effects of crosswinds was proposed. The model analyzed major factors affecting the geometrical parameters of the flame, including the inertial force caused by the crosswind, thermal buoyancy from flame combustion, and the interaction and separation distance between the two fires. Additionally, correlations between the flame tilt angle and the horizontal flame length scale of the two adjacent flames were proposed. It was also demonstrated that the ground-received downstream radiative heat fluxes were the dominant parameters determining flame spread. Based on the assumption of the flame geometry of two adjacent parallel fires, the viewing factor was revised, and the relationship between the position of the radiant point and the horizontal length of the flame was considered in the flame model. Furthermore, based on the updated viewing factor of two parallel adjacent flames, a prediction model of ground-received radiative heat fluxes was proposed, which successfully estimated the variation of ground-received downstream radiative heat flux profiles along the centerline of the two parallel flames under crosswind conditions. This estimation is crucial for future fire research, particularly cross-wind-related experiments.

Verification of a metamaterial with gradient particles and its near-field radiative heat transfer property

Verification of a metamaterial with gradient particles and its near-field radiative heat transfer property

Experimental Study of Near-field Radiative Heat Transfer Between Large-Area Polar Dielectric Films

Utilizing polar dielectric films can improve the performance of near-field thermophotovoltaic system. To confirm the enhancement of near-field radiative heat transfer (NFRHT) achieved by large-area polar dielectric films, we built an experimental setup and observe NFRHT between two 250 nm-thick SiO2 films on intrinsic Si substrate with an area 5 × 5 mm2. The two films are supported by SiO2 nano-spacers with a height of 302 nm. Temperature difference between the two films varies from 13 K to 42 K at room temperature. The observed near-field radiative heat flux closely matches the theoretical values, which surpasses substrate-only system by up to 9.87 times and could reach up to 7.45 times that of blackbody radiation due to excitation of the surface photon polaritons modes. These results demonstrate the effectiveness of polar dielectric films in enhancing NFRHT.

PERFORMANCE OF WATER COOLING FOR RADIATION HEAT FLUX FUEL STORAGE TANK

Full-surface fire on fuel storage tank emits high radiation heat transfer. As a fire protection strategy, the water curtain cooling system is activated to reduce the temperature on the adjacent tank surface. Therefore, the present work predicts and analyses the radiation heat flux and the maximum flame temperature of different types of fuels. Further, this analyses the effect of fuel total mass on radiation heat flux and maximum flame temperature and observes the effect of distance between two tanks on radiation heat flux distribution. The relationship between water cooling flow rate and outlet water temperature that absorbed radiation heat flux has been studied. The study has been conducted by using the Consequence modeling software trial version. The modeling setup of the tank is 17 m in height with 65 m inner diameter, and the meteorological data used are 5.4 m/s wind speed with north wind direction at atmospheric pressure in order to imitate the worst-case fire scenario. The results reveal that the gasoline fuel emitted the highest heat flux value of 11.03 kW/m2 and the raw gasoline sample emits the lowest heat flux value of 9.14 kW/m2. Furthermore, the total mass of the fuel shows no effect on the maximum flame temperature of 958.51°C. According to the findings, the critical tank distancing is 36 m and thus the appropriate tank distancing of 40 m is highly recommended by the standard. The result shows that the water cooling rate of 4.1 lpm/m2 is an excellent practice of water cooling to cool down the temperature of the fuel tank which is exposed to radiation heat flux.

Thermal Performance Evaluation of a Single-Mouth Improved Cookstove: Theoretical Approach Compared with Experimental Data

This work aims to address the knowledge gap in the thermal efficiency performance of a locally made cookstove in Mali. Despite the fact that the thermal efficiency of cookstoves is a crucial aspect of cooking, the performance of commercially produced cookstoves in Mali has not been thoroughly studied. In this context, the thermal efficiency of a single-mouth biomass stove has been investigated using a theoretical and experimental approach. First, the fundamental principles of physics for the three forms of heat transfer were applied. Then, the theoretical thermal efficiency of the stove was calculated based on the percentage share of energy gains and losses for the respective heat transfer modes. This analysis shows that the highest energy gain is achieved by radiation heat transfer from the flame and the fuel bed, followed by convection heat transfer to the bottom and sides of the pot, respectively. In order to validate the findings, the theoretical results have been compared with the experimental data at a case study site in Katibougou, Mali. Accordingly, the experimental thermal efficiency is slightly lower than the theoretical value, with a measured value of 27% compared to the theoretical value of 31.45%. The theoretical thermal efficiency can be closer to the experimental efficiency if the combustion losses caused by incomplete combustion of the fuel are taken into account.

Entropy and radiative heat transfer analysis in water-based nanofluid flow with Catteneo-Christov heat flux

Entropy and radiative heat transfer analysis in water-based nanofluid flow with Catteneo-Christov heat flux

Radiative heat transfer analysis of a concave porous fin under the local thermal non-equilibrium condition: application of the clique polynomial method and physics-informed neural networks

Radiative heat transfer analysis of a concave porous fin under the local thermal non-equilibrium condition: application of the clique polynomial method and physics-informed neural networks

Radiative flow of clay nanoparticles on the lubricity of Williamson drilling fluids across a vertical surface in a Darcy-Brinkman porous medium

Drilling fluids are essential for extracting gases and oils from rocks and soil. To increase drilling fluid efficiency, clay nanoparticles are crucial. The use of clay particles in drilling fluids increases their thermal conductivity, viscosity, and boiling point, hence giving resilience to high temperatures and controlling fluid costs. Therefore, this research examines the convection radiative flow and heat transfer incorporated in the Williamson nanofluid with a heat source/sink. The effective thermophysical properties of clay nanofluid are represented quantitatively by using Maxwell-Garnett and Brinkman's formulas. The leading PDEs with physical boundary conditions that control the flow phenomena are predetermined. These PDEs are converted into ODEs using the similarity method, and dual solutions are then found by using an effective bvp4c solver. The effects of mixed convective, permeability, Williamson constraint, heat source/sink, nanoparticle volume fraction, and radiation parameters were all thoroughly studied quantitatively and theoretically. The Nusselt number and skin friction are calculated and displayed in tabular form as well as graphical form along with the velocity and temperature profiles. Multiple solutions are observed in the shrinkable sheet as well as the buoyancy assisting flow. The findings demonstrate that the Nusselt number rises noticeably when volume concentration increases. In addition, the permeability parameter expands the boundary layer thickness in the lower solution, while the contrary behavior is observed in the upper solution.

Differential models for radiative heat transfer in scattering media: applications in aerospace engineering

Differential models for radiative heat transfer in scattering media: applications in aerospace engineering

Experimental and numerical investigation on the effect of ease allowance of clothing on thermal comfort

The heat transfer within the microclimate of clothing directly affects the thermal sensation of the human body, holding significant implications for both heat dissipation and cold protection. To investigate the variations in the heat transfer performance of the microclimate under the clothing influenced by distinct air gap thicknesses and diverse body postures, twelve female subjects participated in experiments wearing T-shirts with various ease allowances, conducting tasks in both sitting and standing positions within a climate chamber set at 20 °C and 50 % RH. Physiological parameters and subjective evaluations of comfort were recorded. Additionally, we constructed a three-dimensional model of the air gap featuring realistic morphology for numerical simulations of microclimatic heat transfer in a standing posture. The experimental results indicate that air gap thickness significantly impacts core temperature, mean skin temperature, local skin temperature, and thermal sensation. While postural differences did not show statistical significance, temperatures and thermal sensations were generally higher in the sitting position. Based on the results of numerical simulation, under this environmental condition, approximately 27 % of heat transfer was through radiation, with both the percentage of radiative heat transfer and the overall heat flux increasing with greater ease allowance. Furthermore, airflow under the clothing became more disorganized at thicker air layers, primarily concentrating in folds, hems, and sides of the body. This study provides a theoretical support for the workwear design and similar clothing and helps to reduce energy consumption in office environments.

New correlations for focusing effect evaluation of the light metal layer in the lower head of a nuclear reactor in case of severe accident

In case of a severe accident (SA) in a nuclear reactor, the core heats up and materials melt and relocate to the lower head of the vessel. In such configuration, stratification occurs between the oxide and metal phases present in the melt. When the metal phase is lighter than the oxide phase, the maximum heat flux applied to the vessel wall is concentrated at the location of this top metal layer, creating the so-called “focusing effect”. The modelling of the focusing effect is essential for SA codes to properly evaluate the vessel failure time or to demonstrate the vessel integrity, when In Vessel Retention (IVR) strategy is implemented. However, existing correlations used in SA codes for focusing effect modelling have some limitations: if the thickness of the metal layer becomes very small, they predict an extremely high heat flux. Moreover, they were validated with tests using water, whereas the Prandtl number was found to play a significant role in this heat transfer.In this paper, the focusing effect is studied based on 3D Direct Numerical Simulations (DNS) of a cylindrical metal layer, covering all possible metal layer characteristics in terms of geometry and boundary conditions, especially for its top surface where the intensity of radiative heat transfer may vary. The analysis of the fluid behavior and the quantitative results obtained allow to derive new correlations and a new model based on the radial profile of the mean temperature of the system and on the radial profile at the top surface. Results at reactor scale confirm the overestimation of existing 0D model used in SA codes for a thin metal layer and highlight the relevance of the proposed model for focusing effect evaluation during transient situations.

Numerical investigation of thermal soak within engine bay using lattice Boltzmann method

A large amount of heat accumulates in the engine bay for a short time after the engine runs at high load and shuts down, that will lead to thermal damage and thermal fatigue caused by the temperature rise of some heat sensitive components. This paper uses an aero-thermal coupling approach to study the heat transfer problem in the engine bay of an SUV model under thermal soak conditions. Due to the transient characteristics of the heat transfer process, the natural transient CFD software developed based on the LBM method is used to study the engine bay heat transfer during the 400 s key-off soak process. The analysis reveals that convection and radiation are the main heat transfer modes in the early stage of hot immersion (0–120 s), and conduction only makes a significant contribution in contact with high temperature sources. The radiation and convection are the key contributors to heat transfer processes of engine bay during soak, but the efficiency of radiation heat transfer decreases with the increase of time, whereas the efficiency of convection heat transfer is not always reduced, it will increase and then decrease with the increase of time. The coupling method established can predict the thermal state in the engine bay well, and is in good agreement with the experimental results. The results show that the error in the engine coolant temperature is less than 1 °C, and the error in the temperature of the heat-sensitive components is less than 5 °C. Finally, the potential risks of thermal damage and thermal fatigue states were assessed, providing an important reference for the control design of cooling fan running time after key-off.