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In this research, the coupling between non-gray radiation and separation convection flow in a duct is investigated numerically. Distributions of absorption coefficients across the spectrum are obtained from the HITRAN2008 database. The full-spectrum k-distribution method is used to deal with the non-gray part of the problem, while the gray radiation calculations are performed using the Planck mean absorption coefficient. To find the divergence of radiative heat flux distribution, the radiative transfer equation (RTE) is solved by the discrete ordinates method (DOM). The effects of radiation-conduction parameter, scattering coefficient and wall emissivity on thermal behaviors are investigated for both gray and non-gray mediums. In addition, the results of gray medium are compared with non-gray results as a real case. The results show that in many cases, use of gray simulations is not acceptable and leads to significant errors, especially in non-scattering medium with high values of radiation-conduction parameter and wall emissivity.

This paper presents a numerical analysis of interaction between non-gray radiation and laminar forced convection flow in a duct with an expansion. Distributions of absorption coefficients across the spectrum (50 cm −1 < η < 20000 cm −1 ) are obtained from the HITRAN2008 database. The full spectrum k-distribution method (FSK) is used to deal with the non-gray part of the problem, while the gray radiation calculations are carried out using the Planck mean absorption coefficient. In addition, the results of non-gray medium are compared with the gray results in order to judge if the differences between these two approaches are significant enough to justify the usage of non-gray models. Results show that for air mixtures with different mole fractions of CO 2 and H 2 O, use of gray model for the radiative properties may leads to considerable errors and should be eschewed.

Combined convection and radiation in simultaneously developing laminar flow and heat transfer is numerically considered with a discrete-direction method. Coupled heat transfer in absorbing emitting but not scattering gases is presented in some cases of practical situations such as combustion of natural gas, propane and heavy fuel. Numerical calculations are performed to evaluate the thermal radiation effects on heat transfer through combustion products flowing inside circular ducts. The radiative properties of the flowing gases are modeled by using the absorption distribution function (ADF) model. The fluid is a mixture of carbon dioxide, water vapor, and nitrogen. The flow and energy balance equations are solved simultaneously with temperature dependent fluid properties. The bulk mean temperature variations and Nusselt numbers are shown for a uniform inlet temperature. Total, radiative and convective mean Nusselt numbers and their axial evolution for different gas mixtures produced by combustion with oxygen are explored. nema

PurposeThe paper aims to present the advanced mathematical and numerical models of conjugated heat and mass transfer in a multi-layer protective clothing, human skin and muscle subjected to incident external radiative heat flux.Design/methodology/approachThe garment was made of three layers of porous fabric separated by the air gaps, whereas in the tissue, four skin sublayers and muscle layer were distinguished. The mathematical model accounted for the coupled heat transfer by conduction and thermal radiation with the associated phase transition of the bound water in the fabric fibres and diffusion of the water vapour in the clothing layers and air gaps. The skin and muscle were modelled with two equation model which accounted for heat transfer in the tissue and arterial blood. Complex thermal and mass transfer conditions at the internal or external boundaries between the fabric layers, air gaps and skin were assumed. Special attention was paid to modelling of thermal radiation emitted by external heat source, for example, a fire, penetrating through the protective clothing and being absorbed by the skin and muscle.FindingsTemporal and spatial variations of temperature in the protective garment, skin and muscle, as well as volume fractions of the water vapour and bound water in the clothing, were calculated for various intensity of incident radiative heat flux. The results of numerical simulation were used to estimate the risk of the first-, second- and third-degree burns.Research limitations/implicationsBecause of the small thickness of the considered system in comparison to its lateral dimensions, the presented model was limited to 1D heat and moisture transfer. The convective heat transfer through the clothing was neglected.Practical implicationsThe model may be applied for design of the new protective clothing and for assessment of thermal performance of the various types of protective garments. Additionally, the proposed approach may be used in the medicine for estimation of degree of thermal destruction of the tissue during treatment of burns.Originality/valueThe novel advanced thermal model of the multi-layer protective garment, skin and muscle layer was developed. For the first time, non-grey optical properties and various optical phenomena at the internal or external boundaries between the fabric layers, air gaps and skin were accounted for during simulation of thermal interactions between the external heat source (e.g. a fire), protective clothing and human skin.