Influence Of Radiative Heat Transfer Research Articles

A thermo-mechanical coupling model for simulating the re-entry failure evolution mechanism of spacecraft propulsion module

A three-dimensional dynamic thermo-mechanical coupling model (TMCM) has been developed to analyze re-entry evolution mechanism of spacecraft propulsion module subjected to aerodynamic/thermal loads. Firstly, a general dynamic thermo-mechanical coupling finite element algorithm is proposed based on TMCM. The accuracy of TMCM is verified by comparison with analytical solutions of one-dimensional problem and numerical solutions of three-dimensional problem. Then, the TMCM for a complex propulsion module is established, in which all the fuel tanks, gas cylinders, support frame and cone platform are taken into account. The external heat flux and pressure of the whole propulsion module are calculated by gas-kinetic unified algorithm (GKUA). Finally, the dynamic thermo-mechanical evolution mechanism of each component structure and the influence of radiation heat transfer are discussed separately during re-entry 90 km-75 km altitude range, and materials considered are stainless steel, carbon fiber composite and aluminum alloy. Simulation results reveal the evolution process of the temperature field, displacement field and stress field of the whole propulsion module. The TMCM provides a powerful tool for accurate prediction of disintegration failure during spacecraft re-entry through thermal and structural analysis of the structure.

Influence of radiation heat transfer on parallel hot-wire thermal conductivity measurements of semi-transparent materials at high temperature

This paper presents a study of the influence of the radiation transfer on the thermal conductivity measurement in a parallel hot-wire method at high temperature. Simulations of the temperature evolution are first carried out with COMSOL Multiphysics® using the coupled conduction–radiation module based on the P1 approximation for the radiation calculation. A wide range of conditions were investigated: a low and a high density insulator were considered with various radiation characteristics (purely scattering, absorbing and scattering, purely absorbing) and with temperature varying up to 1500°C. This study enables the determination of the validity limit of the modeling of the temperature by a purely conductive model with an equivalent conductivity based on the Rosseland approximation. When this assumption is valid, a new estimation process was proposed to improve the estimation accuracy of the thermal properties. A calibration process of the distance between the hot-wire and the thermocouple has also been proposed and validated, enabling a more accurate estimation of the volume heat capacity.An experimental study carried out on three insulating materials with densities ranging from 581kgm−3 to 910kgm−3 and at temperatures ranging from 20°C to 1200°C confirms the results of the theoretical study. Finally, a method enabling the estimation of the extinction coefficient from thermal conductivity measurements at various temperatures is presented and successfully applied to the three tested materials.

Influence of Radiation Heat Transfer on Mc-Si Ingot during Directional Solidification: A Numerical Investigation

Influence of Radiation Heat Transfer on Mc-Si Ingot during Directional Solidification: A Numerical Investigation

Influence of Radiation Heat Transfer on Parallel Hot-Wire Thermal Conductivity Measurements of Semi-Transparent Materials at High Temperature

Influence of Radiation Heat Transfer on Parallel Hot-Wire Thermal Conductivity Measurements of Semi-Transparent Materials at High Temperature

Simulation of the GOx/GCH4 Multi-Element Combustor Including the Effects of Radiation and Algebraic Variable Turbulent Prandtl Approaches

Multi-element thrusters operating with gaseous oxygen (GOX) and methane (GCH4) have been numerically studied and the results were compared to test data from the Technical University of Munich (TUM). A 3D Reynolds Averaged Navier–Stokes Equations (RANS) approach using a 60° sector as a simulation domain was used for the studies. The primary goals were to examine the effect of the turbulent Prandtl number approximations including local algebraic approaches and to study the influence of radiative heat transfer (RHT). Additionally, the dependence of the results on turbulence modeling was studied. Finally, an adiabatic flamelet approach was compared to an Eddy-Dissipation approach by applying an enhanced global reaction scheme. The normalized and absolute pressures, the integral and segment averaged heat flux were taken as an experimental reference. The results of the different modeling approaches were discussed, and the best performing models were chosen. It was found that compared to other discussed approaches, the BaseLine Explicit Algebraic Reynolds Stress Model (BSL EARSM) provided more physical behavior in terms of mixing, and the adiabatic flamelet was more relevant for combustion. The effect of thermal radiation on the wall heat flux (WHF) was high and was strongly affected by spectral models and wall thermal emissivity. The obtained results showed good agreement with the experimental data, having a small underestimation for pressures of around 2.9% and a good representation of the integral wall heat flux.

SOFC modelling considering radiation heat transfer

In this study, the influence of radiation heat transfer within a planar SOFC is investigated. The numerical model is made by performing two-dimension mathematical model describing mass, momentum and heat transport phenomena coupled with electrochemical reactions. The finite volume method is used to solve the governing equations. Compared with literature results, the simulations show that radiation reduces temperature gradients and has a significant effect on enhancing heat transfer within the SOFC and counter balancing thermal dissipation induced by activation, concentration and ohmic polarisations. Thus, it must be included for an accurate model.

The propagation of weak shock waves in non-ideal gas flow with radiation

In the present paper, the evolutionary behavior of weak shock waves propagating in an unsteady one-dimensional flow in non-ideal radiating gas is analyzed. The effect of thermal radiation under optically thin limit is included in the energy equation of the governing system. The method of asymptotic analysis is used to derive the transport equation describing the propagation of waves under the high-frequency conditions which is also used to determine the time of first wave-breaking conditions. The equation governing the propagation of acceleration waves is also obtained. Furthermore, the movement of disturbance in the shape of saw-tooth profile is discussed. The effect of parameter of non-idealness under the influence of radiative heat transfer, on the decay of sawtooth profile is analyzed.

Influence of radiative heat transfer on the sublimation of a single chromium (III) β-diketonate particle in the superheated mixture of vapor-inert gas

The paper presents the results of numerical simulation of nonstationary sublimation of spherical particles of Cr(acac)3, floating in the volume of a binary mixture (argonsuperheated vapor of precursor) in a reactor with hot walls. The influence of the vapor content, reactor wall temperature and radiative heat transfer on the kinetics of sublimation/desublimation are analyzed. The characteristic times of induction and total sublimation, as well as the intensity of mass entrainment from the surface of particles of different sizes are determined. The influence of radiation from the hot walls of the sublimator on these parameters is determined.

Influence of radiative heat transfer on the thermal characteristics of nanofluid flow over an inclined step in the presence of an axial magnetic field

This research analyzes the influences of radiation heat transfer and Brownian movement on the thermal characteristics of nanofluid flow over an inclined step in the presence of an axial magnetic field. The Rosseland approximation is applied to simulate the divergence of radiative heat flux in the energy equation. The Al2O3–H2O and CuO–H2O nanofluids are considered as the working fluid. The $${\text{KKL}}$$ correlation is used for modeling the Brownian movement influence on the effective viscosity and thermal conductivity. The impacts of radiation parameter $$\left( {0 \le Rd \le 1} \right)$$, nanoparticles concentration $$\left( {0 \le \phi \le 0.04} \right)$$ and Lorentz force $$\left( {0 \le Ha \le 60} \right)$$ on temperature fields, mean bulk temperature and convective, radiative and total Nusselt numbers are examined with full details. The results show that the impact of CuO nanoparticles on the average of total heat transfer rates is greater that the influence of Al2O3 nanoparticles on them. Besides, the highest values of total heat transfer rates occur in the absence of magnetic field and for the highest values of $$Rd$$ and $$\phi$$ parameters.

Coupled DSMC-Monte Carlo radiative transfer modeling of gas dynamics in a transient impact-generated lunar atmosphere

Volatile-rich impacts on nominally airless solar system bodies such as the Moon can give rise to collisional, transient atmospheres, traces of which may be preserved at cold, permanently shadowed regions near the lunar poles. Understanding the physical mechanisms that influence gas dynamics and volatile transport in an impact-generated atmosphere is critical to interpreting the lunar polar volatile record. Here, we investigate the influence of radiative heat transfer on the structure of an impact-generated atmosphere, an issue that previous work has not addressed in detail. We develop a Monte Carlo radiative transfer model for the attenuation and absorption of thermal radiation by a three-dimensional, evolving, non-uniform, rarefied water vapor atmosphere, accounting for spontaneous emission at the molecular level, as well as radiation from the Sun and the lunar surface. This radiative transfer model is coupled to Direct Simulation Monte Carlo (DSMC) simulations of an impact-generated lunar atmosphere. We find that the trapping of heat by atmospheric water vapor causes characteristic atmospheric shock structures to become more diffuse than if the gas were modeled as transparent to radiation. Trapping of thermal radiation also allows infalling vapor to retain more energy, increasing the efficacy of transport of water vapor to the lunar night side by day side winds, and reducing the overall rate of volatile loss in the short-term. Cold trap deposition patterns are also affected. Accounting for radiative heat transfer also has consequences for temperature-sensitive physical and chemical processes in a collisional atmosphere – for instance, dense regions of the modeled impact-generated atmosphere remain sufficiently warm that condensation is unlikely.

Influence of radiative heat transfer on the sublimation of a single chromium (III) and zirconium (IV) β-diketonate particle in the argon-helium gas mixture

The paper presents a physical and mathematical model of nonstationary sublimation of single spherical particles of volatile chromium (III) and zirconium (IV) β-diketonates, floating in the flow of a binary argon-helium mixture in a reactor with cold walls. The influence of the carrier gas composition and radiative heat transfer on the kinetics of sublimation has been analyzed. The addition of helium to the carrier gas is shown to increase the intensity of sublimation. The cold walls of reactors decrease the temperature of a particle and increase the time of its sublimation due to the radiative cooling.

Combined Natural Convection and Surface Radiation Inside Vented Triangular Enclosure - An Experimental Study

In the present experimental study, the influence of Opening ratio on the chamber temperature in case of vented triangular enclosure with hot base plate has been undertaken. Due to more flow passage, the average air temperature in the enclosure decreases by 12% for OR of 0.25 and 13% for OR of 0.5 compared to OR of 0.125. Similar trend is observed for Rayleigh number with a rise of 73% in OR 0.5 compared to OR of 0.125. Further, the influence of radiation heat transfer in the natural convection based enclosure is also studied. This kind of investigation is useful in the design and analysis of electronic cooling systems.

Combined Natural Convection and Surface Radiation Inside Vented Triangular Enclosure - An Experimental Study

In the present experimental study, the influence of Opening ratio on the chamber temperature in case of vented triangular enclosure with hot base plate has been undertaken. Due to more flow passage, the average air temperature in the enclosure decreases by 12% for OR of 0.25 and 13% for OR of 0.5 compared to OR of 0.125. Similar trend is observed for Rayleigh number with a rise of 73% in OR 0.5 compared to OR of 0.125. Further, the influence of radiation heat transfer in the natural convection based enclosure is also studied. This kind of investigation is useful in the design and analysis of electronic cooling systems.

The influence of radiation heat transfer on the prediction of air flows in rooms under natural ventilation

Scale experiments that use water of different salinities to represent air at different temperatures are a common tool used to investigate room air ventilation. However, it has been shown that these experiments cannot replicate the effects of radiation heat transfer in a room. This paper illustrates the importance of accounting for radiative effects when modeling airflow, especially regarding the air temperature profile. Computational fluid dynamics simulations were performed of flow in heated rooms with and without radiation. It was found that when radiation was ignored the temperature of the air surrounding the occupants was significantly lower, by 2–4°C, than when including its effects. In addition, the surface temperature of the heat sources was consistently higher (up to 17°C) when ignoring radiation. Finally, air velocity in the space was higher in simulations that included radiation. These differences have an important impact on the predicted thermal comfort of the occupants, since neglecting radiative heat transfer would result in an inaccurate estimation of operative temperature. We conclude that water scale models do not provide an accurate description of flow behavior in a space, so desired thermal and flow conditions might not be achieved in buildings designed or assessed using water scale models. For these reasons, theoretical models or computer simulations that omit radiation will also give misleading predictions of room temperature distribution.

The Influence of Thermal Radiation on Effective Thermal Conductivity in Porous Material

Effective thermal conductivity is an important parameter of porous materials for measurement of heat insulation performance. Two-dimensional geometrical models based on micrographs of real material were constructed in this paper and the finite element approach was applied for thermal analysis, the effective thermal conductivity was calculated. The influence of radiation heat transfer, temperature, and porosity on thermal conductivity were analyzed. The results show that conduction heat transfer plays an important role in total heat transfer and the influence of radiation heat transfer was small at low temperature. Because of the increase in radiation heat transfer, the temperature gradient decreased obviously at high temperature and the heat flux lines passed through the pores and became relatively smooth; thus the radiation heat transfer plays an important role in total heat transfer at high temperature and the influence of radiation heat transfer cannot be ignored. Thermal conductivity for a high porosity value will be greater than thermal conductivity for a low porosity value at high temperature. This paper provides guidance for predicting thermal conductivity and reducing the heat transfer efficiency of porous materials at high temperature.

Effect of radiative heat transfer on determining thermal conductivity of semi-transparent materials using transient plane source method

The theoretical basis of transient plane source method is the unsteady differential equation of heat conduction which is suitable for opaque medium. Extremely low density materials such as aerogels and foaming materials are not opaque for thermal radiation at high temperature. For these semi-transparent materials, radiation will participate in the thermal transport process. When applying transient plane source method to measure the thermal conductivity of semi-transparent materials, the existence of thermal radiation within the materials will affect the test accuracy. In present study, the effect of radiative heat transfer on determining thermal conductivity of semi-transparent materials using transient plane source method is numerically studied. The results show that the thermal conductivity of semi-transparent materials measured by transient plane source method will be overestimated at temperature higher than 600K and extinction coefficient less than 2000m−1 where radiative heat transfer is dominant. The deviation increases with temperature and reaches to 19.6% at 1000K for materials with extinction coefficient of 500m−1. It illustrates that the thermal conductivity of semi-transparent materials measured by transient plane source method has taken into account part of the influence of radiative heat transfer within the materials.

Investigation of exhaust gas temperature distribution within a furnace of a stoker fired boiler as a function of its operating parameters

Abstract Distribution of the exhaust gas temperature within the furnace of a grate boiler greatly depends on its operating parameters such as output. It has a considerably different character than temperature distributions in other types of boilers (with pulverised or fluidised bed), as it varies considerably across the chamber. Results presented in this paper have been obtained through research of a grate-fired hot water boiler with a nominal rating of some 30 MW. Measurements have been taken by introducing temperature sensors into prearranged openings placed in the boiler side walls. Investigation has been carried out for different output levels. Tests involved thermocouples in ceramic coating and aspirated thermocouples. The latter were used to eliminate influence of radiative heat transfer on measured results. Values obtained with both methods have been cross-checked.

Numerical study of radiation effect on the municipal solid waste combustion characteristics inside an incinerator

Due to its advantages of high degree volume reduction, relatively stable residue, and energy reclamation, incineration becomes one of the best choices for Municipal Solid Waste (MSW) disposal. However, detailed measurements of temperature and gas species inside a furnace are difficulty by conventional experimental techniques. Therefore, numerical simulation of MSW incineration in the packed bed and gas flow field was applied. In this work, a three dimensional (3-D) model of incinerator system, including flow, heat transfer, detailed chemical mechanisms, and non-gray gas models, was developed. Radiation from the furnace wall and the flame formed above the bed is of importance for drying and igniting the waste. The preheated air with high temperature is used for the MSW combustion. Under the conditions of high temperature and high pressure, MSW combustion produces a variety of radiating gases. The wavelength-depend radiative properties of flame adopted in non-gray radiation model were obtained from a statistical narrow-band model. The influence of radiative heat transfer on temperature, flow field is researched by adiabatic model (without considering radiation), gray radiation model, and non-gray radiation model. The simulation results show that taking into account the non-gray radiation is essential.

The Influence of Radiative Heat Transfer and Hall Current on MHD Flow in a Vertical Rotating Channel with Slip Condition

In this paper the effects of Hall current on MHD free convection flow in a vertical rotating channel filled with porous medium have been studied. A uniform magnetic field is applied in the direction normal to the plates. The entire system rotates about an axis normal to the planes of the plates with uniform angular velocity The temperature of one of the plates varies periodically and the temperature difference of the plates is high enough to induce radiative heat transfer. The effects of various parameters on the velocity and temperature field are shown graphically. Also the results on Skin Frication and Nusselt Number are shown in tables.

Numerical simulations of the industrial circulating fluidized bed boiler under air- and oxy-fuel combustion

Measured and numerical results of air-fuel combustion process within large scale industrial circulating fluidized bed (CFB) boiler is presented in this paper. For numerical simulations the industrial compact CFB boiler was selected. Numerical simulations were carried out using three-dimensional model where the dense particulate transport phenomenon was simultaneously modelled with combustion process. The fluidization process was modelled using the hybrid Euler-Lagrange approach. The impact of the geometrical model simplification on predicted mass distribution and temperature profiles over CFB boiler combustion chamber two kinds of geometrical models were used, namely the complete model which consist of combustion chamber, solid separators, external solid super-heaters and simplified boiler geometry which was reduced to the combustion chamber. The evaluated temperature and pressure profiles during numerical simulations were compared against measured data collected during boiler air-fuel operation. Collected data was also used for validating numerical model of the oxy-fuel combustion model. Stability of the model and its sensitivity on changes of several input parameters were studied. The comparison of the pressure and temperature profiles for all considered cases gave comparable trends in contrary to measured data. Moreover, some additional test was carried out the check the influence of radiative heat transfer on predicted temperature profile within the CFB boiler.