Radiative Heat Flow Research Articles

Effect of Organic–Inorganic Mixed Intumescent Flame Retardants on Fire-Retardant Coatings

Expandable graphite (EG) was modified with a charring agent and organic–inorganic hybridized intumescent flame retardants (MEG) were synthesized. This study uses a cone calorimeter (CCT) and a DaqPRO 5300 radiation heat flow meter (Fourtec, Tel Aviv, Israel) to evaluate the fire-resistant properties influenced by MEG on intumescent fire-retardant coatings. The impact of MEG on the thermal degradation of these coatings was investigated through the use of thermogravimetric analysis (TGA). The results obtained by CCT demonstrated that the incorporation of MEG markedly diminished the heat release rate and total heat release rate of the coating, in addition to enhancing the char residue compared to coatings with only expandable graphite (EG). Furthermore, TGA results demonstrate that adding MEG increases the weight of the char residue at elevated temperatures, suggesting improved thermal stability. Based on these findings, MEG exhibits a synergistic flame-retardant effect when combined with intumescent fire-retardant (IFR) systems. This synergy not only improves the flame-retardant properties of the coatings but also enhances their overall thermal stability, making MEG a promising additive for developing more efficient fire-retardant materials. Thus, MEG-modified coatings offer superior protection against fire hazards, highlighting their potential for practical applications in fire safety.

Time-modulated near-field radiative heat transfer

Near-field radiative heat transfer has recently attracted increasing interests for its applications in energy technologies, such as thermophotovoltaics. Existing works, however, are restricted to time-independent systems. Here, we explore near-field radiative heat transfer between two bodies under time modulation by developing a rigorous fluctuational electrodynamics formalism. We demonstrate that time modulation can result in the enhancement, suppression, elimination, or reversal of radiative heat flow between the two bodies, and can be used to create a radiative thermal diode with an infinite contrast ratio, as well as a near-field radiative heat engine that pumps heat from the cold to the hot bodies. The formalism reveals a fundamental symmetry relation in the radiative heat transfer coefficients that underlies these effects. Our results indicate the significant capabilities of time modulation for managing nanoscale radiative heat flow.

Comparative analysis of two-dimensional and three-dimensional modeling of heat transfer during operation of a gas infrared heater indoor

Relevance. It is proposed to heat local work areas with systems based on gas infrared heaters, capable of directing radiative heat flow to reduce heating costs in large premises. However, the widespread use of gas infrared heaters is hampered by the existing difficulties with the preliminary assessment of convective-radiative heat flows movement, on which the number and location of heating devices depends. The preliminary assessment is complicated by the need in some cases for 3D modeling of complex physical processes. It is necessary to evaluate the possibility of replacing labor-intensive 3D modeling with a method for calculating a heating system using gas infrared emitters based on a 2D approach to reduce the time spent on calculations. Aim. To prove that the use of a two-dimensional model of the processes under consideration makes it possible to obtain the main characteristics of the thermal regime of the premises, making it possible to replace spatial modeling. Objects. Heating system with a light-type gas infrared heater and an air exchange system. Methods. Two-dimensional and three-dimensional mathematical modeling of conjugate heat transfer processes using the finite element method. Mathematical modeling was carried out in the COMSOL Multiphysics software environment using the modules: “Heat Transfer Interface in Liquids”, “Radiation between Surfaces” and “Turbulent Flow, k-ε Interface”. Results. The article presents the results of mathematical modeling performed in three-dimensional and two-dimensional formulations. The distribution of temperatures in the air and enclosing structures, as well as the flow lines of heated air and air, which was heating, in the volume of the premise are presented. The results of two-dimensional and three-dimensional modeling were compared. Satisfactory similarity of the calculated average air temperatures in the local working area was established based on the results. The difference was less than 2℃ for different spatial modeling approaches.

Numerical simulation of leakage jet flame hazard of high-pressure hydrogen storage bottle in open space

The jet fire is a common type of fire accident in high-pressure hydrogen storage bottles. It is crucial to conduct research on the thermal radiation hazards resulting from on-board hydrogen storage bottle leaks, leading to jet fires within 35 MPa. Additionally, accurately and swiftly calculating the characteristic parameters of hydrogen jet flames, such as flame geometry and radiation heat flow, is of utmost importance. To study the jet fire hazard caused by high-pressure hydrogen storage cylinder leaks, a simplified model of the hydrogen storage cylinder was established using FLUENT software for numerical simulation analysis. The study analyzed the impact patterns of high-pressure hydrogen leakage jet flames under different scenarios, including leakage aperture, leakage pressure and ambient wind speed. The results demonstrate a positive correlation between the leakage aperture and pressure with the size of the jet flame and the extent of thermal radiation damage. The larger the leakage aperture and pressure, the larger the hydrogen jet flame size. The higher the peak value of the flame thermal radiation, the greater the hazard range. Additionally, the temperature of the stable axis of the jet flame rises with increasing leakage aperture. As the leakage pressure rises, the thermal radiation of the flame also increases. Conversely, as the ambient wind speed increases, the flame length, the burn radius, and the thermal radiation range decreases, but the high-temperature heat range expands. The empirical formula between flame length and leakage pressure and leakage aperture under different environmental wind speeds is obtained by data fitting, which can be used as a priori prediction of flame length under wind speed conditions.

Functional interactions between coat structure and colour in the determination of solar heat load on arid living kangaroos in summer: balancing crypsis and thermoregulation

Interactions of solar radiation with mammal fur are complex. Reflection of radiation in the visible spectrum provides colour that has various roles, including sexual display and crypsis, i.e., camouflage. Radiation that is absorbed by a fur coat is converted to heat, a proportion of which impacts on the skin. Not all absorption occurs at the coat surface, and some radiation penetrates the coat before being absorbed, particularly in lighter coats. In studies on this phenomenon in kangaroos, we found that two arid zone species with the thinnest coats had similar effective heat load, despite markedly different solar reflectances. These kangaroos were Red Kangaroos (Osphranter rufus) and Western Grey Kangaroos (Macropus fuliginosus).Here we examine the connections between heat flow patterns associated with solar radiation, and the physical structure of these coats. Also noted are the impacts of changing wind speed. The modulation of solar radiation and resultant heat flows in these coats were measured at wind speeds from 1 to 10 m s−1 by mounting them on a heat flux transducer/temperature-controlled plate apparatus in a wind tunnel. A lamp with a spectrum like solar radiation was used as a proxy for the sun. The integrated reflectance across the solar spectrum was higher in the red kangaroos (40 ± 2%) than in the grey kangaroos (28 ± 1%). Fur depth and insulation were not different between the two species, but differences occurred in fibre structure, notably in fibre length, fibre density and fibre shape. Patterns of heat flux within the species’ coats occurred despite no overall difference in effective solar heat load. We consider that an overarching need for crypsis, particularly for the more open desert-adapted red kangaroo, has led to the complex adaptations that retard the penetrance of solar radiation into its more reflective fur.

Research on Calibration Technology of Radiation Heat Flow Sensor

Research on Calibration Technology of Radiation Heat Flow Sensor

Исследование термического разрушения некоторых видов строительных материалов в результате воздействия радиационного теплового потока от очага пожара

The article presents the results of experimental studies of the thermal destruction of certain types of combustible building materials treated with fire retardant impregnations as a result of exposure to radiation heat flow from a model heat source with a characteristic temperature corresponding to the maximum temperature in the front of a ground forest fire. Data were obtained on the depth and rate of thermal destruction of materials.

Analysis of Magnetohydrodynamic Oscillatory Convective Radiative Heat Flow of Reactive Nanofluid Containing MoS2 and SiO2 Nanoparticles with Velocity Slip

This paper aims to investigate the unsteady oscillatory flow of water-based nanofluids MoS2 and SiO2 past a parallel plate channel filled with a saturated porous medium. The basic equations are solved analytically using the perturbation technique subject to the appropriate boundary conditions. A numerical evaluation of the analytical results is performed, and the effects of various physical parameters on velocity, temperature, and concentration profiles within the boundary layer are analyzed. Molybdenum disulfide MoS2 nanoparticles are well known for their low friction coefficient, good catalytic activity, and excellent physical properties. At the same time, Silicon dioxide (SiO2) nanoparticles are treated to have a porous structure, very high surface activity, and adsorption properties, which makes them suitable for developing high-capacity antimicrobial agents. Hence these nanoparticles can be considered for Nanoscale elements’ performance to make rigorous thermal quality nano liquids. Thus from engineering curiosity, the skin friction coefficient, Nusselt number, and Sherwood numbers are evaluated for significant parameters at cold and heated walls by utilizing MoS2 and SiO2 nanoparticles. It would give rise to novel features that can revolutionize biology, medicine, catalysis, and other smart fields. Furthermore, graphs and tables are used to describe a comparative study of the water-based nanofluids MoS2 and SiO2. It is found that when the radiation parameter Ra is increased by 200%, the average heat transfer rate at the heated channel wall containing MoS2 and SiO2 nanoparticles in the base fluid is decreased by 6.9% and 8.3%, respectively. Further, it is found that SiO2-water nanofluid has more effectiveness towards heat transfer compared to MoS2-water nanofluid.

Study on predicting the radiant heat flow rate of floor surface of radiant floor heating

Radiant heat flow rate of radiant surface is crucial for radiant floor heating design and terminal selection. We found that the present empirical formula to predict radiant heat flow rate of radiant surface has limits under varied room size and surface emissivity circumstances. Wall insulation conditions also have substantial influences on the operating efficiency of floor radiant heating. Adopting machine learning algorithms and backward selection method, a two-layer Neural Network model was demonstrated to have good accuracy and requisite relevant features for new empirical formula was identified. The new formula containing the information of room depth, weighted radiant surface area, insulation conditions, indoor air temperature and radiant surface temperature as independent variables exhibits great accuracy with R-squared of 0.97 and RMSE of 2.74. The substitution of AUST with indoor air temperature can increase the prediction accuracy. Analysis reveals structural pattern and indicates interaction between wall insulation and non-radiative surface with low emissivity. We propose the use of non-radiant surfaces with low emissivity as a passive energy-saving technique for radiant floor heating. And the updated empirical formula can increase its application scenarios, and aid promote application of FRH and new passive technique.

Scaled experimental study on the initial oil thickness effect on the combustion characteristic of the typical transformer insulating oil

Compared with mineral oil, plant insulation oil has a higher flash point, excellent natural degradation ability, and higher electrical insulation. It is expected to become the main component of transformer insulation oil, but the fire safety of this oil needs to be further analyzed and improved. In this paper, a cone calorimeter was used to test the combustion of typical plant insulating oil (camellia seed oil, soybean oil) and mineral oil (25# mineral oil) under different radiant heat flows and initial oil thickness. The combustion parameters such as ignition time, heat release rate, and carbon generation rate were measured. The combustion characteristics of 25# mineral oil were greatly affected by radiative heat flow and oil thickness. The peak heat release rate and carbon generation rate of mineral oil under high heat flow (50 kW/m2) were significantly higher than those under low heat flow (25 kW/m2) and increased with the increase of initial oil thickness. Plant insulating oil (camellia seed oil and soybean oil) had similar laws, but the peak value of the heat release rate and carbon generation rate of soybean oil were relatively small. Petrella fire risk assessment method showed that the fire risk ranking in descending order was mineral oil, camellia seed oil, and soybean oil, which provided a reference for the further popularization and application of plant insulation oil transformer.

Experimental study on fire characteristics of sidewall fires in a long-narrow compartment with multiple lateral openings

This experimental study delves into the fire characteristics within a long and narrow compartment equipped with multiple lateral openings. The investigation encompasses aspects such as radiant heat flow, temperature distribution, and smoke layer height. The presence of lateral openings introduces asymmetry in suction, resulting in augmented radiative heat flow on the rear side of the fire source compared to the front and left sides. Smoke stratification remains stable, with minimal temperature influence from the fire source power at one opening and negligible impact at the other. Employing a customized two-dimensional method for thermal estimation, our experimental data display lower results than previous predictions due to structural disparities. The utilization of the N-percentage rule unveils two discernible regions in smoke layer height behavior: stable and decreasing, a pattern consistent across varying heat release rates. These insights offer valuable predictive tools for discerning fire characteristics in elongated, restricted compartments with multiple lateral openings. Consequently, this study enhances comprehension and informs safety measures within such configurations, contributing to the broader field of fire safety engineering.

Exploration of diffusion-thermo and thermo-diffusion on the nonlinear radiative heat flow of a conducting fluid over a permeable surface

The featured problem explores the impact of cross-diffusion on the two-dimensional electrically conducting flow of a viscous liquid over a nonlinearly stretching sheet through a permeable medium. An inclusion of radiative heat energizes the heat transport phenomenon whereas the solutal transfer enriches by the conjunction of the chemical reaction. To justify the behavior of electromagnetic radiation, the Rosseland approximation is used by considering nonlinear thermal radiation. Further, the convective boundary conditions also affect the flow properties. The approachable transformations are employed to get a suitable non-dimensional form of the governing equations for the formulated problem. Due to the complex nature of the distorted equations, the system of equations is solved using an in-built code bvp5c predefined in MATLAB. The computation is carried out for the involvement of the suitable values of contributing parameters on the flow characteristics and along with the simulations of the rate coefficients. Further, the assigned particular parameters present an outcome that validates with a good correlation. Finally, the important outcomes are — enhanced suction due to the permeability of the surface augments the fluid velocity whereas the trend is reversed in the case of injection. The augmentation in the fluid temperature is exhibited for the radiating heat but the reacting species attenuates the fluid concentration.

MHD 3D Mixed Upper Convective Flow of Maxwell Nanofluid Flow Past in the Presence of Diffusion Thermo and Thermophoresis Effect using Nonlinear Radiative Heat Flux

This article aims to investigate the impact of nanoparticles and magnetohydrodynamics (MHD) on the transfer of heat and mass using a three-dimensional upper-convected Maxwell (UCM) nanofluid flow across a stretched surface. A nonlinear radiative heat flow was included in formulating the equation that describes energy. The nonlinear partial differential equations of the issue are transformed into ordinary differential equations utilizing the similarity transformation. These equations are then solved using the well-known shooting approach in conjunction with the Runge-Kutta integration process of order four. To increase the dependability of our findings, make use of the MATLAB. On the velocities, temperatures, and concentrations of the particles, the graphical and numerical representations of the effects of the main parameters, such as the Dufour parameter, the Brownian motion parameter, the Prandtl number, the thermophoresis parameter, and the magnetic parameter, are presented. It has been shown that the flow velocity decreases as a function of both the linear and nonlinear thermal radiation parameters. In addition, increasing values of the Brownian motion parameter have the effect of reducing the nanoparticle concentration profile

Thermal Diffusion and Diffusion Thermo Effects on MHD 3D Mixed Upper Convective Flow of Maxwell Nanofluid Flow Past using Nonlinear Radiative Heat Flux

This article aims to investigate the effect of nanoparticles and magnetohydrodynamics (MHD) on the transfer of heat and mass using a three-dimensional upper-convected Maxwell (UCM) nanofluid flow across a stretched surface in the presence of diffusion thermo and thermal diffusion. A nonlinear radiative heat flow was included in formulating the equation that describes energy. The nonlinear partial differential equations of the issue are transformed into ordinary differential equations utilizing the similarity transformation. These equations are then solved using the well-known shooting approach in conjunction with the Runge-Kutta integration process of order four. To increase the dependability of our findings, we additionally make use of the bvp4c built-in function that is available in MATLAB. On the velocities, temperatures, and concentrations of the particles, the graphical and numerical representations of the effects of the main parameters, such as the Dufour parameter, the Brownian motion parameter, the Prandtl number, the thermophoresis parameter, and the magnetic parameter, are presented. It has been shown that the flow velocity decreases as a function of both the linear and nonlinear thermal radiation parameters. In addition, increasing values of the Brownian motion parameter have the effect of reducing the nanoparticle concentration profile

An Innovative External Heat Flow Expansion Formula for Efficient Uncertainty Analysis in Spacecraft Earth Radiation Heat Flow Calculations

Thermal uncertainty analysis of spacecraft is an important method to avoid overdesign and underdesign problems. In the context of uncertainty analysis, thermal models representing multiple operating conditions must be invoked repeatedly, leading to substantial computational costs. The ray tracing calculation of Earth infrared and albedo radiation heat flux is an important reason for the slow calculation speed. As the rays emitted during external heat flux calculations under different operating conditions are independent and unconnected, the rays produced across various conditions are effectively wasted. In this study, the external heat flow equation is thoroughly expanded and the derived factors are clustered and analyzed to develop a novel formula for calculating external heat flow. When this formula is employed to compute the uncertain external heat flux, only one condition necessitates ray tracing, while the remaining conditions utilize simple matrix operations in place of complex ray tracing. Within the aforementioned procedure, certain matrices demonstrate sparse characteristics. The optimization calculations for these matrices can, therefore, benefit from the application of sparse matrix optimization algorithms. Using a spacecraft as an example, the uncertain external heat flux calculation outcomes of the new and traditional formulas are compared and assessed. The findings reveal that the new formula is highly suitable for estimating uncertain Earth radiation heat flow, with a marked improvement in efficiency. The accuracy is essentially equivalent to that of the traditional formula and the calculation precision can be dynamically adjusted to meet user requirements. The methodology can be further generalized to assess the uncertainties associated with radiative external heat fluxes for other celestial bodies within the solar system. This offers a valuable theoretical framework for addressing the uncertainties in the thermal design of deep space exploration vehicles.

Nonsimilar solution of hybrid nanofluid over curved stretching surface with viscous dissipation: A numerical study

In this research work, numerical simulations and mathematical modeling are introduced for the mixed convection hybrid nanofluid flow over a curved stretching surface. The energy equation is modeled subjected to viscous dissipation, a heat source with radiative heat flow. Convective and velocity slip conditions are assumed at the stretchable surface. The Eckert number and Grashof number contained the independent variable "s" which is not suitable for the dimensionless parameters. In this regard, the problem is solved by a nonsimilar approach. The nonsimilar approach has not been tried before on a curved stretching surface. Furthermore, alumina and copper are taken as nanoparticles, and blood is taken as a base fluid. A nonsimilarity transformation is used to transform the governing equation into dimensionless (PDEs). Converting these PDEs into ODEs by using the local nonsimilarity method. The familiar Bvp4c is used to perform numerical computations for a dimensionless nonlinear system. Significant results for velocity and temperature profiles for different parameters are comprehensively presented and discussed. Results indicated that increasing the volume fraction of the base fluid increased the fluid velocity and temperature. The volume fraction of alumina and copper nanoparticles decreases the fluid velocity and boundary layer thickness. Furthermore, the slip condition decreases the fluid velocity, and the fluid becomes static if the slip parameter value is greater than fifty.

Development of Infrared Reflective Textiles and Simulation of Their Effect in Cold-Protection Garments

Two ways of to enhance the heat insulation of cold-protecting garments are studied using the mathematical model, which describes the coupled transport of temperature, humidity, and bound and condensed water. The model is developed in a one-dimensional formulation. The thermal radiation transport is explicitly considered by the subdivision of the heat flux into radiative and conduction parts. The model is utilized to study the improvement of heat-insulating properties of cold protective garments using aerogel materials and thin infrared reflective textile layers. Special attention is paid to the technological aspects of manufacturing such reflective textiles. The numerical investigations show that the use of infrared reflective textiles is the most effective of the two studied methods. Due to the reflection of the radiant heat flow coming from the human body, the skin temperature rises and the thermal insulation of clothing is significantly improved.

Numerical investigation of the ground-based thermal environment experimental approaches to reveal the ice-sublimation phenomenon inside lunar regolith

In recent years, the Moon, as the closest celestial body to the Earth, has become the foremost target of human exploration outward. Some lunar exploration missions and studies have shown that ice may exist in the polar regions of the Moon. Water is very important for human survival. The ice mining and utilization is based on the understanding of the sublimation mechanism. Simulation of ground-based tests is an effective means to explore the sublimation of ice. Therefore, in this paper, the thermal environment of Shackleton Crater and the particle size distribution of typical lunar soils are analyzed as the basis of parameter settings for the ground test. Four operating conditions are established for ground tests, including the influence of heat sink temperature, vacuum level, particle size distribution and dry soil density. The larger the radiation heat flow, the higher the heat sink temperature, the smaller the vacuum degree, the larger the average particle size, resulting in a larger sublimation rate. The decrease of density makes the sublimation process faster and then slower. The sublimation process proceeds fastest when the dry soil density is 1200 kg/m3. The heat sink temperature has the greatest effect on the sublimation process, and the vacuum has the least effect. When the radiation heat flow ranges from 39.01 W/m2 to 45.63 W/m2 at the heat sink temperature of 120 K, the maximum sublimation rate is 5.79E-15 kg/s, the maximum sublimation area is 1.93E-9 m2 and the maximum sublimation heat flow is 1.59E-8 W. However, the effect of vacuum degree and particle size distribution on the sample temperature variation is not significant, due to the small order of magnitude of the sublimation heat flow compared to the radiation and conduction heat flows. This paper gives a range of parameters for ground-based simulation experiments and points out the microscopic changes of the ice sublimation process, which provides ideas for the next ground-based experiments and the exploitation of water-ice resources on the Moon.

Radiative heat exchange driven by acoustic modes between two solids at the atomic scale

In the near field (for separation distances smaller than the thermal wavelength, of the order of some microns at ambient temperature), the radiative heat flow between two solids at different temperatures can exceed the blackbody limit by several orders of magnitude. Furthermore, at the atomic scale, close to contact, the vibrational modes of the crystal lattice are expected to play an important role in the heat exchange. While the contribution of acoustic phonons tunnel-ing due to Van der Waals forces and electrostatic interactions near the surface has been investigated [1–5], the radiative contribution of the acoustic modes has been neglected so far. Under the local assumption (wavevector k ≈ 0), optical modes are independent from the acoustic modes, and are the sole responsible for the thermal radiation for distances larger than a few nanometers. However at subnanometer distances, the electromagnetic response of solids is nonlocal (k ≠ 0) and both acoustic and optical modes are coupled, contributing together to the radiative heat exchange. In order to demonstrate the role of this contribu-tion, we calculate [6] the nonlocal dielectric permittivity of magnesium oxide (MgO) using molecular dynamics. In conjunction with fluctuational electrody-namics calculations, we are able to highlight the role of radiation between two polar crystals produced by acoustic modes compared to the expected results from the local theory. We show that this additional contribution can become the dominant channel for radiative heat exchanges at atomic scale in the cryo-genic regime (below 100 K). Since the acoustic vibration modes can be excited with the help of piezoelectric transducers, our work opens the possibility to the control of radiative heat exchanges at atomic scale using external mechanical actuation.

Assessment of hybrid-quasi-Monte Carlo method efficiency in Earth radiative external heat flow calculation

Assessment of hybrid-quasi-Monte Carlo method efficiency in Earth radiative external heat flow calculation