Radiation Convection Heat Transfer Research Articles

A nonstationary problem of complex heat transfer

A nonstationary problem of radiative-convective heat transfer in a three-dimensional region is studied in the framework of the diffusion P 1-approximation of the radiative heat transfer equation. The problem is proved to be uniquely solvable nonlocally in time, and a stationary equilibrium state is shown to be asymptotically stable.

Numerical simulation of heat exchange at a gas-solid medium flow past an evaporating semitransparent film

Numerical solution was obtained for the Stefan problem applied to non-stationary radiative-convective heat transfer during turbulent flow past a horizontal evaporating semitransparent melt film; the turbulent flow takes place for hot gas mixture carrying solid particles. The flowing film was heated intensively by radiation from an external heat source. Radiation passes through the gas-solid particle layer and the film and interacts with medium for a limited spectral interval. Simulation offers temperature fields and velocity fields for the boundary layer and the film. Simulation results are the basis for analysis of influence of radiation on dynamics of temperature fields and on the velocity of evaporation boundary.

Convection–radiation heat transfer in solar heat exchangers filled with a porous medium: Homotopy perturbation method versus numerical analysis

The case of combined conduction–convection–radiation heat transfer usually occurred in solar thermal usages is the aim of the present study. This type of combined heat transfer in heat exchangers filled with a fluid saturated cellular porous medium is investigated. The flow is modeled by the Darcy–Brinkman equation. The steady state model of this combined heat transfer is solved semi-analytically based on the homotopy perturbation method (HPM) and numerically based on the finite difference method. No analytical solution has been previously proposed for the problem. Effects of porous medium shape parameter (s) and radiation parameters (Tr and λ) on the thermal performance are analyzed. Furthermore, a discussion on the accuracy and limitations of the HPM in this kind of problems is represented. This study shows that semi-analytical methods (like HPM, VIM, DTM, and HAM) can be used in simulation and prediction of thermal performance of solar energy harvesting systems.

A Compressible Approach to Solve Combined Natural Convection-Radiation Heat Transfer in Participating Media

The need for accurate prediction of combined natural convection-radiation heat transfer in participating media has resulted in developing a few different numerical methods with different capabilities. One important aspect in treating high-thermobuoyant flow fields is to impose the compressibility effects in predictions. The Literature shows that most previous research has used incompressible algorithms to solve the combined natural convection-radiation problem. However, the research in pure natural-convection heat transfer problems has shown that the Boussinesq assumption will not result in solutions with sufficient accuracies in domains with high temperature variations. In this work, we develop a hybrid incompressible-compressible method to solve the combined natural convection-radiation heat transfer in a participating medium without addressing the Boussinesq approximation. Our results show that there are significant differences between the compressible and incompressible results in treating such high-thermobuoyant flow fields. We also show that the compressibility effects become more dominant in combined natural convection-radiation problems than in the pure natural-convection problem. So, we conclude that use of the Boussinesq assumption cannot be definitely recommended in treating thermobuoyant flow fields with strong to moderate temperature gradients. Indeed, the current developed algorithm can be used to avoid the inaccuracies resulting from the incompressible treatment of such flow fields.

Soret-Dufour Effects on Hydromagnetic Non-Darcy Convective-Radiative Heat and Mass Transfer over a Stretching Sheet in Porous Medium with Viscous Dissipation and Ohmic Heating

The present study is devoted to investigate the effects of Soret and Dufour on the mixed convection flow, heat and mass transfer over a stretching sheet in the presence of viscous dissipation, Ohmic heating, thermal radiation in porous medium. Numerical solutions for the coupled governing equations are obtained by using the fifth-order Runge-Kutta-Fehlberg method with shooting technique. Important features of flow, heat and mass transfer characteristics for different values of the physical parameters are analyzed and discussed. Numerical results reveal that the magnetic field and inertia coefficient reduce the skin friction but reverse effects are seen on local Nusselt number.

Численный анализ конвективно-радиационного теплопереноса в замкнутой воздушной полости с локальным источником энергии

Численный анализ конвективно-радиационного теплопереноса в замкнутой воздушной полости с локальным источником энергии

Comprehensive analytical study for convective–radiative continuously moving plates with multiple non-linearities

Thermal processing of metals may be moving, as in hot rolling, forging or extrusion, to shape materials in standard forms such as plates, sheets, rods, tubes and structural sections. The purpose of the present paper is to analyze the problem of convective–radiative heat transfer from a continuously moving plate with multiple nonlinearities. The thermal conductivity and surface emissivity of the plate’s material are considered as temperature-dependent. The heat transfer coefficient within the energy equation is assumed to be power-law function of temperature. The calculations are carried out by using the differential transformation method (DTM) which is an analytical solution technique that can be applied to various types of differential equations. The accuracy of the DTM solution is confirmed by comparing the obtained results with those from an analytical solution for a special case and previous publications. Results illustrate the effects of Peclet number, thermal conductivity, surface emissivity, convection–conduction parameter, radiation–conduction parameter, and dimensionless convection and radiation sink temperatures on the temperature of the plate.

Numerical Analysis of Spatial Unsteady Regimes of Conjugate Convective-Radiative Heat Transfer in a Closed Volume with an Energy Source

Unsteady regimes of convective-radiative heat transfer in a cubic enclosure with finitely thick heat-conducting walls in the presence of a constant-temperature energy source have been modeled mathematically under the conditions of convective heat exchange with the environment. A mathematical model has been formulated in dimensionless variables “vector potential–vorticity vector–temperature;” the model was realized numerically by the finite-difference method. An analysis of radiative heat transfer has been made on the basis of the surface-radiation approximation with the balance method in Polyak’s version. Three-dimensional temperature and velocity fields and dependences for the average Nusselt number have been obtained; they reflect the influence of the reduced emissivity factor of interior surfaces of enclosing walls, of the relative thermal conductivity, and of the unsteadiness factor on the flow regimes and heat transfer.

Natural Convection-Radiation from a Vertical Base-Fin Array with Emissivity Determination

Experiments have been conducted to determine the emissivity for black chrome coated and uncoated aluminum surfaces. The emissivity of the surfaces is estimated considering combined convection radiation heat transfer and observed to be a constant in the range of 60 to 110 o C. The combined heat transfer coefficients from black chrome coated vertical base vertical fin array of size 70 x 70 mm consisting of 22 aluminum fins with a fin spacing of 10 mm by natural convection and radiation has been determined at different heat inputs. Theoretical analysis of single fin geometry of constant thickness considering both convection and radiation has been used to predict the temperature distribution and heat flow. The theoretical values of heat flow estimated for a fin array is in good agreement with the experimental observations validating the emissivity of the surface. The experimental data is further validated with the equations of Nusselt presented by Churchill and Chu.

Theoretical analysis of an optimal control problem of conductive–convective–radiative heat transfer

The problem of optimal heat removal from a three-dimensional domain is considered. The specific of the study consist in accounting for the radiative heat transfer. The so-called P1 approximation of the radiative heat transfer equation is used, which reduces the model to a nonlinear elliptic system. A problem of optimal boundary control of this system is considered. The solvability of the control problem is proved, and necessary optimality conditions of first order are derived. Examples of non-singularity of these conditions are given.

The unique solvability of a complex 3D heat transfer problem

Conductive–convective–radiative heat transfer in a scattering and absorbing medium with reflecting and radiating boundaries is considered. The P1 approximation (diffusion model) is used for the simplification of the original problem. The existence of bounded states of the diffusion model is proved. The uniqueness of solutions is established under certain assumptions.

Analytical solution to convection-radiation of a continuously moving fin with temperature-dependent thermal conductivity

In this article, the simultaneous convection-radiation heat transfer of a moving fin of variable thermal conductivity is studied. The differential transformation method (DTM) is applied for an analytic solution for heat transfer in fin with two different profiles. Fin profiles are rectangular and exponential. The accuracy of analytic solution is validated by comparing it with the numerical solution that is obtained by fourth-order Runge-Kutta method. The analytical and numerical results are shown for different values of the embedding parameters. DTM results show that series converge rapidly with high accuracy. The results indicate that the fin tip temperature increases when ambient temperature increases. Conversely, the fin tip temperature decreases with an increase in the Peclet number, convection-conduction and radiation-conduction parameters. It is shown that the fin tip temperature of the exponential profile is higher than the rectangular one. The results indicate that the numerical data and analytical method are in a good agreement with each other.

Developing an efficient regime for the thermal stabilization of polyacrylonitrile roving in a “Vulon” furnace

A mathematical model is constructed to describe conjugate radiative-convective heat transfer in the working space of a “Vulon” furnace, which is designed for the thermal stabilization of raw materials used in the production of carbon fibers. A program was written in the language C++ to realize the model in the environment Builder 6.0. The program was used to study the thermal performance of the furnace, and temperature regimes were devised to allow problem-free thermal stabilization of polyacrylonitride rovings. It is shown that the stabilization operation can be automated by controlling the power supplied to electric heaters installed in the channels of the furnace.

Simulation of the radiation-convective heat transfer in multinozzle assemblies of rocket engines

The method and results of numerical modeling of the radiation-convective heat transfer and thermal state in the systems of multinozzle rocket-engine (RE) assemblies are presented. The method is implemented in a form of a software module entered as the component into the program of calculation of the nonsteady thermal state of the RE nozzles. The results of calculation by the consolidated program are given, and the two-dimensional thermal fields on the external and internal surfaces of mouthpieces of the four-nozzle liquid rocket engine allow us to refine the thermal state of the nozzles themselves and evaluate the radiation heat flows in the engine module.

Unsteady radiative-convective heat transfer on a radiating surface

Research of radiation-convective heat exchange on radiating surfaces at natural and forced convection is complex mathematical task and here we obtain approximate analytical formulations for this process. We consider two dimensional unsteady heat transfer between solid surface and fluid under the natural laminar convection within optically transparent grey media. Also we assume constant thermo-physical properties except density which is decreasing linearly with temperature. Complex radiative-convective unsteady heat transfer approximately can be considered as a multi-stage process. At the beginning heat transfer coefficient is time dependent but almost independent on longitudinal coordinate. Afterwards heat transfer coefficient becomes dependent on longitudinal coordinate but does not change over time. Analytic formulations obtained for those two stages could be merged along the "time-space" characteristic basing on the equality of heat flows and temperatures there. Solutions are constructed using asymptotic expansions. Theoretical analysis of the solutions revealed the following: effect of radiation leads to a change in the heat transfer coefficient from the values that are characteristic to the second order boundary conditions to the values that are characteristic for the first order boundary conditions. The rate of this transition depends on ß radiation coefficient. Experimental research confirmed correctness of the simplifications introduced.

Combined heat transfer of radiation and forced convection flow of participating gases in a three-dimensional recess

This research work presents a numerical investigation of three-dimensional combined convection-radiation heat transfer over a recess including two inclined steps in a horizontal duct. To simulate the inclined surface boundaries, the blocked off method is employed for both fluid mechanic and radiation problems. The fluid is treated as a gray, absorbing, emitting and scattering medium. In numerical solution of the governing equations including conservation of mass, momentum and energy, the three-dimensional Cartesian coordinate system is used. These equations are solved numerically using the CFD techniques to obtain the temperature and velocity fields. Discretized forms of the governing equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, all of the convection, conduction and radiation terms are presented in the energy equation. For computation of radiative term in energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM) to find the divergence of radiative heat flux distribution inside the radiating medium. The effects of radiation-conduction parameter, optical thickness and albedo coefficient on heat transfer behavior of the system are presented. Comparison of numerical results with the available data published in open literature shows a good agreement.

Численный анализ сопряженного конвективно-радиационного теплопереноса в замкнутой полости, заполненной диатермичной средой

Численный анализ сопряженного конвективно-радиационного теплопереноса в замкнутой полости, заполненной диатермичной средой

Mathematical simulation of convective-radiative heat transfer in a ventilated rectangular cavity with consideration of internal mass transfer

Mathematical simulation of the nonstationary regimes of heat-and-mass transfer in a ventilated rectangular cavity with heat-conducting walls of finite thickness in the presence of a heat-generating element of constant temperature has been carried out with account for the radiative heat transfer in the Rosseland approximation. As mechanisms of energy transfer in this cavity, the combined convection and the thermal radiation in the gas space of the cavity and the heat conduction in the elements of its fencing solid shell were considered. The mathematical model formulated in the dimensionless stream function–vorticity vector–temperature–concentration variables was realized numerically with the use of the finite-difference method. The streamline, temperature-field, and concentration distributions reflecting the influence of the Rayleigh number (Ra = 104, 105, 106), the nonstationarity (0 < τ ≤ 1000), and the optical thickness of the medium (τλ = 50, 100, 200) on the regimes of the gas flow and the heat-and-mass transfer in the cavity have been obtained.

Numerical analysis of laminar forced convection recess flow with two inclined steps considering gas radiation effect

In this work, a numerical analysis of combined convection–radiation heat transfer over a recess including two inclined backward and forward facing steps in a horizontal duct is presented. The fluid is treated as a gray, absorbing, emitting and scattering medium. Discretized forms of the continuity, momentum and energy equations are obtained by the finite volume method and solved using the SIMPLE algorithm, while the blocked off method is employed in simulation of the inclined surfaces. The radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM). Numerical results reveal that the radiation–conduction parameter, optical thickness, step inclination angle and recess length have considerable effects on heat transfer behavior of the recess flow. Comparison of numerical results with the available data published in open literature shows a good consistency.

Characteristics of Rosseland and P-1 approximations in modeling nonstationary conditions of convection-radiation heat transfer in an enclosure with a local energy source

Numerical modeling is performed for nonstationary conjugate convection-radiation heat transfer in an enclosure with a local energy source under nonlinear heat exchange with the environment. Two approximations were used for mathematical description of the mechanism of radiation in a gas cavity, namely, Rosseland approximation and differential formulation (or P-1 approach) of the methods of spherical harmonic functions. Comparison of two different approaches to description of the radiation mechanism of energy transfer has made it possible to identify special features of thesemodels. Temperature and stream distribution functions are obtained in a wide range of the governing parameters.