Radiative heat transfer in plane participating media

The problem of radiative heat transfer through a nonisothermal scattering, absorbing and emitting grey medium between reflecting, absorbing and emitting plates is analytically investigated. The solution technique is based on a projectional procedure, equivalent to a variational approach. The results concern the most meaningful physical quantities, and get an improved accuracy with respect to the data available in literature, with extremely low computational time.     

Radiative heat transfer in porous media with spatially-dependent heat generation

We report an investigation of radiative heat transfer in porous radiant burners. The combustion was modeled as a spatially-dependent heat generation. Using the spherical harmonics to solve the equation of transfer, we have obtained the P-11 solution for the net radiative heat flux. Results presented illustrate the radiant output as a function of the position of the combustion zone, the optical thickness and the type of scattering of the porous layer, and the amount of reflection from the distribution chamber.     

Radiative heat transfer during turbulent combustion process

We investigate the radiative heat transfer in a co-flowing turbulent nonpremixed propane-air flame inside a three-dimensional cylindrical combustion chamber. The radiation from the luminous flame, which is due to the appearance of soot particles in the flame, is studied here, through the balance equation of radiative transfer which is solved by the Discrete Ordinates Method (DOM) coupling with a Large Eddy Simulation (LES) of the flow, temperature, combustion species and soot formation. The effect of scattering is ignored as it is found that the absorption dominates the radiating medium. Assessments of the various orders of DOM are also made and we find that the results of the incident radiation predicted by the higher order approximations of the DOM are in good agreement.     

Radiative heat transfer in enhanced hydrogen outgassing of glass

This paper explores the physical mechanisms responsible for experimental observations that led to the definition of “photo-induced hydrogen outgassing of glass”. Doped borosilicate glass samples were placed inside an evacuated silica tube and heated in a furnace or by an incandescent lamp. It was observed that hydrogen release from the glass sample was faster and stronger when heated by an incandescent lamp than within a furnace. Here, sample and silica tube were modeled as plane-parallel slabs exposed to furnace or to lamp thermal radiation. Combined conduction, radiation, and mass transfer were accounted for by solving the one-dimensional transient mass and energy conservation equations along with the steady-state radiative transfer equation. All properties were found in the literature. The experimental observations can be qualitatively explained based on conventional thermally activated gas diffusion and by carefully accounting for the participation of the silica tube to radiation transfer along with the spectral properties of the silica tube and the glass samples. In brief, the radiation emitted by the incandescent lamp is concentrated between 0.5 and 3.0 μm and reaches directly the sample since the silica tube is nearly transparent for wavelengths up to 3.5 μm. On the contrary, for furnace heating at 400 °C, the silica tube absorbs a large fraction of the incident radiation which reduces the heating rate and the H₂ release rate. However, between 0.8 and 3.2 μm undoped borosilicate does not absorb significantly. Coincidentally, Fe₃O₄ doping increases the absorption coefficient and also reacts with H₂ to form ferrous ions which increase the absorption coefficient of the sample by two orders of magnitude. Thus, doped and reacted samples heat up much faster when exposed to the heating lamp resulting in the observed faster response time and larger H₂ release rate.     

Radiative heat transfer from potassium seeded water gas combustion plasma

Radiative heat transfer calculations from a potassium seeded water gas combustion plasma have been made to estimate the radiative heat losses through the walls of a MHD channel. Both molecular combustion products and seed contribute significantly to the total radiation loss from a plasma. The spectral emission properties of CO₂, H₂O, CO and potassium have been taken into account. It has been shown that the contribution of CO to heat flux is very small and, thus, can be neglected. CO₂ and H₂O are the primary contributors to the radiation from the combustion products. At MHD temperatures, 55–80% of the contribution to heat flux from the combustion products comes from bands lying up to 2.7 μm in the near infrared. It has been shown that accurate knowledge of absorption cross-section data is essential to predict the radiative heat transfer from potassium. It has been estimated that 25–30% of the total radiative heat flux is from the potassium seed.     

Radiative properties and heat transfer characteristics of fiber-loaded silica aerogel composites for thermal insulation

The radiative properties and heat transfer in fiber-loaded silica aerogel composites were investigated using modified anomalous diffraction theory in a combined heat conduction and radiation model. The randomly parameterized 2-D fiber distribution was generated to simulate a very realistic material structure. The finite volume method was then used to solve a two flux radiation model and the steady-state energy equation to calculate the effective thermal conductivity of the composite. The numerical results provide theoretic guidelines for material designs with optimum parameters, such as the inclination angle, diameter and length-to-diameter ratio of the fibers. The results show that the fiber extinction coefficient increases as the fiber length-to-diameter ratio is reduced or the fiber inclination angle is increased. The effective thermal conductivity of the fiber-loaded aerogel can be reduced by reducing the fiber length-to-diameter ratio and the inclination angle and by moderately increasing the fiber volume fraction. The 4–6 μm diameter silicon fibers are optimum for high-temperature thermal insulation.     

Evaporation heat transfer of liquid nitrogen on microstructured surface at high superheat level

Liquid nitrogen, as a coolant, is generally applied in cell vitrification cryopreservation. It takes heat from the carrier with cell samples through its violent evaporation on the carrier surface. As a result, the temperature of the carrier plunges dramatically. This article focuses on the unsteady evaporation heat transfer characteristics of liquid nitrogen on a microstructured surface etched into the frozen carrier surface at a high superheat level. The heat flux and evaporation heat transfer coefficient of liquid nitrogen were investigated using a lumped capacitance method. The experimental results showed that the cooling rate of the thin film evaporation on the microstructured surface is obviously higher than that of pool boiling, which is currently being used for cell cryopreservation. The heat flux and the evaporation heat transfer coefficient work together to present a parabolic trend with the superheat decreasing during this heat transfer process. Besides, the microstructure of the surface has an important effect on the evaporation heat transfer of liquid nitrogen. The larger the thin film evaporation zone is, the higher the heat transfer coefficient is. The current investigation results in a cell cryopreservation method through vitrification with relatively low concentrations of cryoprotectants.     

Radiative heat transfer to flow of a combustible mixture in a vertical channel

The paper studies the flow of a combustible mixture in a vertical channel in the presence of radiative heat transfer as a model for biomass moving bed gasifiers operating in the temperature range 750–1500 K. The simplistic binary reaction A → B is assumed, and both the optically thick (high density gas) and the optically thin (low density gas) situations are considered for the radiative heat transfer. Analytical and numerical solutions are obtained and discussed quantitatively.     

Radiative heat transfer in a solar air heater covered with a plastic film

This article presents a new set of equations for the radiative balances of the absorber plate and the transparent cover of a solar air heater covered with a plastic film. Air flow is supposed to pass between the absorber plate and the bottom of the collector, while the transparent cover and the absorber plate are separated by an immobile air layer. This configuration is shown to be the best suited for a plastic covered solar air heater used in tropical countries, from a practical point of view.     

Radiative heat transfer to flow of a combustible mixture in a vertical pipe

The flow of a combustible gas in a vertical cylinder, in the presence of radiative heat transfer, affords the closest model to biomass moving bed gasifier operating at temperatures between 750 and 1500 K. This problem forms the subject matter of the paper under the simplistic assumption of a binary reaction A → B. Under the general differential approximation for radiation, the temperature is perturbed about the wall temperature, and the nonlinear differential equations are subsequently integrated in a closed form. Consequences of the effect of the Arrhenius activation energy are discussed quantitatively.     

Radiative heat transfer by flowing multiphase medium-part I. An analysis on heat transfer of laminar flow between parallel flat plates

The multiphase flow of gaseous suspensions of fine particles furnishes high heat transfer characteristics at high and/or extremely high temperatures and at high heat fluxes due to the radiative transfer from heat source to suspensions. The phaseshift of particulate medium improves the overall heat transfer remarkably and from the practical viewpoint there exists important relevance pertinent to the industrial applications.

It is worth having a closer look at the behaviors of the suspensions and the heat transfer mechanism in flowing multiphase media so that the discussions are held concerning the foregoing media in some details.

An analysis is carried out on the laminar flow between parallel plates by taking into account of thermal radiation and the results illustrate the temperature profiles of fluid and dispersed phase, respectively, and the heat transfer characteristics for the wide ranges of dimensionless parameters such as conduction y, and radiation interaction parameter, loading ratio of particles, optical depth of duct, heat transfer between the two phases and so forth. Reference to the temperature profiles reveals the facts that while the temperature gradient in the vicinity of the heating surface increases due to the presence of particulate phase, the cupmixing mean temperature is raised appreciably by thermal radiation through the dispersed medium. In consequence, the contributions of suspensions on heat transfer are drastic, particularly in high temperature cases. Alternatively the correlations between the foregoing dimensionless parameters are also examined in current study.     

Fluid flow and heat transfer in an optical fiber coating process

The optical fiber coating process, using a die and applicator system, was numerically simulated. The coupled partial differential equations, governing the fluid flow and heat transfer, were solved on a transformed, non-uniform, staggered grid. A finite volume method, with conjugate heat transfer, boundary-fitted grid, and variable transport properties, was employed. The pressure was calculated using a SIMPLE-based algorithm. An isothermal case was first modeled, where the effect of the Reynolds number (Re) was studied for different geometries. Different coating fluids were considered. A conjugate boundary condition was employed at the fiber–fluid interface for the non-isothermal flow. A free surface boundary condition was used at the fiber entry into the coating fluid. The meniscus was prescribed on the basis of prior experimental work. Regardless of fiber speed, a circulating flow was observed in the applicator. High shear rates at the dynamic contact point suggest that air can be entrained with a fast moving fiber. It was also found that pressures at the coating fluid inlet did not play a major role, for typical fiber speeds, whereas the thermal conditions that affect the properties of the fluid, such as viscosity, made a significant impact on both the flow and the thermal field. This work could be used to determine the parameters that are critical for improving the quality of the coating, particularly its uniformity, and the production rate.     

Radiative heat transfer analysis of non-Newtonian dusty Casson fluid flow along a complex wavy surface

In this article, numerical solutions are obtained to observe the influence of thermal radiation on Casson particulate suspension flow past a complex isothermal wavy surface. Rosseland diffusion approximation is employed to express the contribution of radiative heat flux over the Casson fluid model. Using coordinate transformations, the two-phase model is converted into a suitable form and then integrated numerically by employing implicit finite-difference method. The numerical results are discussed in detail in terms of shear stress, rate of heat transfer, streamlines, and isotherms. It is found that the rate of heat transfer increases extensively when radiation parameter and mass concentration parameter are penetrated into the mechanism.     

Radiative heat transfer by flowing multiphase medium—part II. An analysis on heat transfer of laminar flow in an entrance region of circular tube

An analysis has been performed on the heat transfer with thermal radiation by flowing gaseous suspensions of solid and/or liquid fine particles in an inlet section of circular tube. The examination of the results on temperature profiles of both phases and heat transfer parameters illustrates that the multiphase medium is pertinent to heat transfer at high and extremely high temperatures because of the absorption behavior of the dispersed phase for thermal radiation and the results are summarized for wide ranges of parameters such as loading ratio, heat transfer characteristics between two phases, optical thickness of a duct, interaction parameter of conduction with radiation, etc. The interactions between the convection to fluid and the radiation are. thereafter, examined in some details.     

Radiative nanofluid flow and heat transfer between parallel disks with penetrable and stretchable walls considering Cattaneo–Christov heat flux model

In this work, we explore the unsteady squeezing flow and heat transfer of nanofluid between two parallel disks in which one of the disks is penetrable and the other is stretchable/shrinkable, in the presence of thermal radiation and heat source impacts, and considering the Cattaneo–Christov heat flux model instead of the more conventional Fourier's law of heat conduction. A similarity transformation is utilized to transmute the governing momentum and energy equations into nonlinear ordinary differential equations with the proper boundary conditions. The achieved nonlinear ordinary differential equations are solved by the Duan–Rach Approach (DRA). This method modifies the standard Adomian Decomposition Method by evaluating the inverse operators at the boundary conditions directly. The impacts of diverse active parameters, such as the suction/injection parameter, the solid volume fraction, the heat source parameter, the thermal relaxation parameter, and the radiation parameter on flow and heat transfer traits are examined. In addition, the value of the Nusselt number is calculated and portrayed through figures.     

Adoption of optical fibres or of optical light films in architecture

The paper aims to discuss the speedy spread of the use of optical fibres or optical light films lighting systems, as an alternative to classical lighting systems in buildings.A series of architectural projects has been selected to provide more evidence about advantages of these new lighting equipement, in terms of thermal and lighting comfort together with low cost energy. As a matter of fact their efficiency has even lead some professionals to use them in some buildings after suppression of the initial lighting system.The fact that the optional fibres or optical light films are used in various spaces has enabled to hope for a development of their applications in interiors and especially public places, in hot contries where heat output from traditional lighting bulbs is more likely to provide discomfort and hence where requirement for air conditionning is unavoidably maximised.