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Steady two-dimensional non-Newtonian second grade fluid is studied under the influence of temperature dependent viscosity and thermal conductivity. The viscosity is assumed to vary inversely as linear function of temperature while the thermal conductivity varies directly as linear function of temperature. Also, effects of radiative heat, viscous dissipation and heat source/sink are considered in the energy equation. The basic governing partial differential equations for the velocity and temperature are transformed to ordinary differential equations (ODEs) using appropriate similarity variables. These coupled nonlinear ODEs have been solved approximately subject to appropriate boundary conditions by Runge–Kutta shooting technique. The quantitative effects of emerging dimensionless physical parameters on the velocity, temperature, skin friction and heat transfer rate are displayed graphically. The numerical investigation of the variable thermo-physical properties of a second grade fluid over a stretching sheet provides an extension to previous work.

WOS:000357543800021; International audience; There is a strong interest in accurately modelling the radiative properties of soot aggregates (also known as black carbon particles) emitted from combustion systems and fires to gain improved understanding of the role of black carbon to global warming. This study conducted a systematic investigation of the effects of overlapping and necking between neighbouring primary particles on the radiative properties of soot aggregates using the discrete dipole approximation. The degrees of overlapping and necking are quantified by the overlapping and necking parameters. Realistic soot aggregates were generated numerically by constructing overlapping and necking to fractal aggregates formed by point-touch primary particles simulated using a diffusion-limited cluster aggregation algorithm. Radiative properties (differential scattering, absorption, total scattering, specific extinction, asymmetry factor and single scattering albedo) were calculated using the experimentally measured soot refractive index over the spectral range of 266-1064 nm for 9 combinations of the overlapping and necking parameters. Overlapping and necking affect significantly the absorption and scattering properties of soot aggregates, especially in the near UV spectrum due to the enhanced multiple scattering effects within an aggregate. By using correctly modified aggregate properties (fractal dimension, prefactor, primary particle radius, and the number of primary particle) and by accounting for the effects of multiple scattering, the simple Rayleigh-Debye-Gans theory for fractal aggregates can reproduce reasonably accurate radiative properties of realistic soot aggregates. (C) 2015 Elsevier Ltd. All rights reserved.

International audience; The oxygen concentration in the oxidizer stream (O-2 + N-2) of laminar coflow ethylene diffusion flames is varied from 17% to 35% in order to study its influence on the flame height, the soot formation/oxidation processes, the smoke point characteristics, and the vertical distributions of radiative flux at a distance of 6.85 cm from the flame axis. Measured values for all the investigated parameters are compared with the predictions provided by a numerical model based on a two-equation semiempirical acetylene-based soot model and on the statistical narrow-band correlated-k model to compute thermal radiation. Predictions are in overall reasonable agreement with the experiments for oxygen indices in the range 19-35%, whereas all the investigated parameters are significantly underestimated for an oxygen index of 17%. Measured flame heights based on CH* emission below, at, or slightly above the smoke point, as well as predicted stoichiometric flame heights, are found to be proportional to xi = (V) over dot(f)[D-infinity In(1 + 1/S)](-1) (T-infinity/T-ad)(0.67), where (V) over dot(f), D-infinity, S, and T-ad are the volumetric flow rate of ethylene, the diffusion coefficient at ambient temperature, the stoichiometric molecular air-to-fuel ratio, and the adiabatic flame temperature. Soot formation processes are found to increase with the oxygen index, leading to higher values of the maximum soot volume fraction and the peak integrated soot volume fraction. In addition, the latter is reached at a nondimensional height (normalized by xi of approximately 0.05, regardless of the oxygen index within the investigated range. Two regimes are evidenced: The first regime, occurring for oxygen indices lower than 25%, is dominated by soot oxidation and is characterized by an enhancement in both the maximum soot volume fraction and the fuel flow rate at the smoke point with the oxygen index. The second regime, occurring for oxygen indices higher than 25%, is dominated by soot formation; the rate of increase in the maximum soot volume fraction with the oxygen concentration is lower than in the first regime, whereas the fuel flow rate at the smoke point decreases. Finally, the peak of radiative flux increases with the oxygen index, but its rate of increase is also found to be considerably reduced for oxygen indices greater than 25%. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The mechanism of damage to a liquefied petroleum gas (LPG) vessel caused by heat radiation was explored, the pressure and the burst pressure of the vessel with a protective layer of polyvinylchloride (PVC) resin were investigated, and a criterion for the failure of the LPG vessel was proposed. The industrial site of Nanjing Refinery was used for the case study, and the effect of the protective layer of PVC resin on the failure of the LPG tank was analyzed. The results showed that the rate of the rise in pressure was significantly reduced by the protective layer and that the time of failure increased rapidly according to the thickness of the protective layer. A highly reliable correlation between the time of failure and the thickness of the protective layer of PVC resin was developed by data fitting. As the theoretical basis for the design of the protective layer of the LPG vessel, a criterion for avoiding the failure of the LPG vessel and the domino effect was proposed to be when the time of failure was larger than the duration of the heat radiation.

We model a lava flow as a one-dimensional flow of a pseudoplastic fluid with viscous dissipation. The flow is horizontally unbounded and is driven downslope by the gravity force. We consider a power-law constitutive equation and we take into account the temperature dependence of the rheological parameters. Given an effusion rate and an initial temperature at the eruption vent, the flow is assumed to cool down by heat radiation. We calculate the heat produced by viscous dissipation as a function of lava temperature and effusion rate. The cooling rate is calculated as a function of the surface temperature and flow rate. Viscous dissipation reduces the cooling rate by an amount which is independent of flow rate. We evaluate the effect of viscous dissipation on the flow thickness and velocity. The effect of dissipation is to decrease the flow thickness and to increase the flow velocity. The effect on flow thickness is greater for smaller flow rates, while the effect on velocity is greater for larger effusion rates. In principle, the model provides a method for estimating the flow rate from in-field measurements of distances and temperatures.

International audience; A Multi-Spectral Reordering (MSR) scheme is introduced to improve the performances of the Spectral-Line Moment-Based (SLMB) modeling for the handling of full spectrum radiative heat transfer calculations in nonuniform media. Using this simultaneous reordering of the spectrum for several thermophysical conditions together with employing approximate formulations to evaluate path-averaged transmission functions for nonisothermal and nonhomogenous gaseous paths, a novel full spectrum gas radiation modeling method in nonuniform gaseous mixtures is constituted. The method is presented in details as well as the building of associated databases for CO2and H2O at atmospheric pressure and for the temperature range of 300-2700 K. The new model is validated against line-by-line reference computations for a series of existing bench-marks and for a flame configuration. The MSR-SLMB modeling is shown to perform accurately and better than the standard SLMB one, while involving reasonable additional computational costs.

In order to research the spread of a fire and the distribution of temperature and gas in high-rise building fires, setting the CCTV North Building Fire as the background, the fire was simulated and analyzed by FDS. The experiment indicates that the basic spread law of fire that mainly spreads on one hand through combustible material on the surface of buildings and then comes to inside, on the other hand spreads from the kindling point to the interior of building and then through lift and corridor from downstairs and finally inside out. The air temperature and gas concentration firstly increase with increasing distance from the fire surface, and then decrease. By changing the maximum combustion temperature and transmit power of the surface decoration materials, it can reduce the influence of surrounding buildings which comes from thermal radiation.

This paper presents a study of the flow and heat transfer of an incompressible Ostwald de-Waele power-law fluid past an infinite porous plate, subject to suction at the plate. The power-law index n satisfies 0 < n< 1 (shear-thinning fluid only) provided that there is suction at the plate. Three cases are studied, namely, (i) the plate with constant surface temperature (CST case), (ii) the plate with prescribed surface temperature (PST case), and (iii) the plate with prescribed heat flux (PHF case). The effects of viscous dissipation and thermal radiation are also considered in the energy equation and the variations of dimensionless surface temperature and dimensionless surface temperature gradient with various parameters are graphed and tabulated. © 2010 The Institution of Chemical Engineers.

Numerical and experimental investigations highlighting the heat and mass transfer phenomena in a laminar co-flowing jet diffusion flame have been carried out. The fuel under consideration is ethylene, with ambient air as the co-flowing oxidizer. The diffusion flame is modeled using a 17-step reduced reaction mechanism with finite rate chemistry and the effects of soot on the radiative heat transfer of the flame have been demonstrated. Soot growth and oxidation processes are studied using a two-equation transport model, while the radiative heat transfer is modeled using the P1 approximation. An in-house finite volume code has been developed to solve the axi-symmetric Navier-Stokes equations in cylindrical coordinates, along with the soot mass fraction, soot number density, energy and species conservation equations. Comparison of predictions with experimental results shows reasonable agreement with regard to the flame height and temperature distribution. A parametric study is also presented, which illustrates the effects of the fuel jet Reynolds number and the flow rate of co-flow air. � 2008 Elsevier Ltd. All rights reserved.

This paper presents a multilayer differential discrete ordinate method to solve the radiative transfer equation for an absorbing, emitting and scattering inhomogeneous plane parallel medium. This method reduces the integro-differential equation into a set of coupled first order ordinary differential equations with two point boundary conditions on using a suitable quadrature scheme. These equations are then solved numerically. Numerical validation of the method for gray medium is done by comparing the results obtained with benchmark cases available in the literature. Validation for a non-gray medium is done by considering a problem concerning radiative transfer from the atmosphere. The brightness temperature at the top of the atmosphere is calculated at various frequencies and validated with those obtained by several other numerical methods. � 2008 Elsevier Ltd. All rights reserved.

An inverse conduction-radiation problem for simultaneous estimation of the conduction-radiation parameter, the optical thickness and the boundary emissivity from a knowledge of the measured temperature profile for combined conduction and radiation in a plane parallel participating medium is presented. A finite volume method is used to solve the "forward" problem, wherein the temperature profile is determined by a solution of the governing equation for a given set of parameters. The inverse problem is treated as an optimization problem, wherein, we minimize the sum of square of residuals between the measured and estimated temperatures. Genetic algorithms are used for the search. The effects of "measurement" errors on the estimated parameters, which are introduced through a random perturbation, are investigated. � 2006 Elsevier Ltd. All rights reserved.

The existing literature on CFD-based coal combustion modelling is applicable mainly for coals of low ash content and the calculations are done on an ash-free basis. In Indian coals, the ash content may be significantly higher, up to 40% or more. Studies reported in the literature show that the mineral matter in the coal may have a number of effects on the combustion characteristics. In the present study, a sensitivity analysis is performed, using the CFD code CFX of AEA Technology, on the likely effect of ash content on the char reactivity, oxygen diffusion rate for char combustion and on the radiative heat transfer parameters. The results show that the effect of enhanced char reactivity is negligible whereas reduced oxygen diffusion rates due to a thicker ash layer may result in a significant reduction in char oxidation rates with a resultant decrease in the peak temperature in the furnace. The global parameters such as the peak temperature and the flue gas temperature remain relatively insensitive to the presence of high ash content. These results are consistent with the experimental observations of Kurose et al. [R. Kurose, M. Ikeda, H. Makino, Combustion characteristics of high ash coal in pulverized coal combustion, J. Fuel 80 (2001) 1447-1455]. � 2006 Elsevier Inc. All rights reserved.

The heating of containerized liquid using microwave radiation is investigated numerically. The numerical model is validated with an earlier experimental study. Unlike previous studies, the turntable rotation is taken into account. The effects of turntable rotation, natural convection, power sources, and aspect ratio of container on the temperature profiles are studied. Detailed results of temperature profiles, stream functions and time evolution of flow field are presented. An attempt is made to physically explain the complex flow pattern due to the effects of rotational and gravitational forces and spatially non-uniform internal heat generation typical in microwave heating. A correlation, for the transient changes of temperature is arrived at. Current studies indicate that turntable rotation does not aid in achieving uniform heating in case of a symmetric heat source. � 2006 Elsevier Ltd. All rights reserved.

A numerical investigation of conjugate convection with surface radiation from horizontal channels with protruding heat sources has been carried out. The flow is assumed to be steady, laminar, incompressible, hydrodynamically and thermally developing. Air is considered as the working fluid. The geometric parameters such as spacing between the channel walls, size of the protruding heat sources, thickness of the substrate and the spacing between the heat sources are fixed. Results are presented to show the effect of parameters such as ReS, Gr S ∗ , kp/kf, ks/kf, ep and es on the fluid flow and heat transfer. A correlation for the non-dimensional maximum temperature is also developed using the method of asymptotic expansions.

In this study, apart from the other studies related to thermal comfort, it is combined that the fundamental equations given in the steady-state energy balance and the empirical relations expressing effects of the thermoregulatory control mechanisms of the body. In the first section of this simulation, body core temperature is calculated by using the equations expressing thermoregulatory control mechanism, the required skin temperature and sweat rate values. Variation of the calculated body core temperature is investigated with the activity level based on required skin temperature and sweat rate values. In the second section of the simulation, heat losses from the body (convection, radiation, evaporation, and respiration) and ratio of the each heat loss mechanism to total heat loss are calculated and discussed in detail.

In this work, the possibility of combining the method of matched asymptotic expansions with Computational Fluid Dynamics (CFD), a technique called ACFD, has been explored, for a new class of problems that involve interaction of radiation with convection. A specific problem of natural convection with surface radiation from an open cavity has been considered to demonstrate the efficacy of the ACFD approach. The work clearly demonstrates the adequacy of the approach and it appears to be an attractive option in the analysis of such multi-mode problems in heat transfer. ? 2003 Elsevier Science Ltd.

We introduce briefly some nonlocal models for heat transfer in conducting and radiating media. The goal is to give an idea of the general mathematical structure and related existence results for such models.

In this paper, a large-scale computational analysis has been undertaken of tubular radiators with fin arrays in which the temperature of the fluid varies along the radiator length. The presence of an optimum fin outer diameter for a given pipe diameter, which is independent of other thermophysical parameters, has been brought out. A set of useful correlations, which will enable the designer to quickly evaluate the performance of the system, is developed for different fin profiles. A design methodology assuming an infinite fluid side heat transfer coefficient has been presented. Comparisons have been made for validating the present calculations.

In the present study the results of a numerical investigation of combined surface radiation and free convection in a square cavity with air as the intervening medium are reported. The computations have been performed for 103 ≤ Gr ≤ 106, with the emissivities of all the walls varying between 0 and 1. Surface radiation reduces the convective heat transfer across the cavity and at the same time contributes to the overall heat transfer by direct radiant heat transfer across the cavity. This “ual” nature of radiation has been qualitatively highlighted in an earlier investigation by the authors. The objective of the present study however, is to give comprehensive correlations for convection and radiation based on the numerical calculations of the coupled problem. The basis for the choice of the form of the various terms in the correlations has also been brought out.