Combined Radiation Convection Research Articles

Comparison of HAM and HPM methods in nonlinear heat conduction and convection equations

Recently, Rajabi et al. (Application of homotopy perturbation method in nonlinear heat conduction and convection equations, Phys. Lett. A 360 (2007) 570–573.) discussed the solutions of temperature distribution in lumped system of combined convection–radiation. They solved a nonlinear equation of the steady conduction in a slab with variable thermal conductivity using both perturbation and homotopy perturbation methods. They claim that homotopy perturbation method (HPM) does not require any small parameter. However, this statement is not true always. Moreover, HPM have no criteria for establishing the convergence of the series solution. In this letter we have explicitly shown that the results of the problem considered in example 2 of (Rajabi, Ganji, Therian, Application of homotopy perturbation method in nonlinear heat conduction and convection equations, Phys. Lett. A 360 (2007) 570–573.) are valid only for 0 ⩽ ε ⩽ 1 . We have used the homotopy analysis method for finding the more meaningful solution.

Application of homotopy perturbation method in nonlinear heat conduction and convection equations

Abstract One of the newest analytical methods to solve nonlinear equations is the application of both homotopy and perturbation techniques. In this Letter, homotopy perturbation method (HPM), which does not need small parameters, is compared with the perturbation method in the field of heat transfer. The justification for using this method is the difficulties and limitations of perturbation and homotopy when used individually. In this research, homotopy perturbation method is used to solve for the temperature distribution in lumped system of combined convection–radiation and also a nonlinear equation of the steady conduction in a slab with variable thermal conductivity.

Combined Convection-Radiation Interaction Along a Vertical Flat Plate in a Porous Medium

An analysis is presented for the convection-radiation interaction heat transfer in boundary-layer flows over a semi-infinite flat plate with temperature dependent effective viscosity embedded in a fluid-saturated porous medium in the presence of a magnetic field. The conservation equations that govern the problem were reduced to a dimensionless form. The system was solved numerically by the Keller-box method. Asymptotic solutions for small and large values of the distance from the leading edge of the plate are presented. The influence of the various parameters entering into the problem on the velocity and heat transfer is studied.

Temperature profiles in composite plates subject to time-dependent complex boundary conditions

The use of composites and multi-layered systems is increasingly important in today’s design industry. Very often these materials must be used within demanding temperature environments. The ability to accurately describe the temperature distribution through multi-layered specimens is, therefore, an essential step in the design process. This paper provides an analytical tool for temperature prediction through multiple layers subject to convection and radiation boundary conditions. The inclusion of radiation, in particular, is novel. A number of examples for various boundary conditions are given, including: fully transient convection, semi-transient radiation, and semi-transient combined convection–radiation. All results agree to better than 95% with FE results under the same boundary conditions.

Combined laminar forced convection and thermal radiation in a helical pipe

The interaction phenomena between laminar forced convection and thermal radiation in a participating medium inside a helical pipe were studied numerically. The P-1 radiation model was applied to the combined convection–radiation simulations. The three-dimensional governing equations for laminar flow and heat transfer were solved with a control-volume finite difference method (CVFDM) with second-order accuracy, and the O-type structure grid was adopted in this study. The effects of thermal radiation on the convective flow and heat transfer were measured by comparing the numerical results with and without thermal radiation. The comparison showed that under the conditions examined in this paper, although the thermal radiation had no significant influence for flow and temperature fields, especially in a fully developed region, it substantially enhanced the total heat transfer in the helical pipe.

Radiation affected compressible turbulent flow over a backward facing step

A numerical analysis has been conducted to examine combined radiation—convection—conduction heat transfer over a backward facing step flow. The LU-SSOR scheme and finite volume method were used to solve the compressible Navier—Stokes equation and energy equation, while the radiative transfer equation was solved by discrete ordinates method (DOM). The thermal behavior has been influenced such that the fluid was heated up faster due to the radiation. Furthermore, the reattachment length was also shrunk because of the reduced adverse pressure gradient. However, the radiative heat flux was found to play some role in the recirculating zone only.

放射•対流炉における強制対流熱伝達

A combined radiation convection furnace has heaters radiating directly to a charge and, in addition, a fin to circulate the air inside it. For the purpose of visualizing and measuring the air flow inside the furnace, the author makes a simple model analogous to the furnace for the air flow inside it and measures the air flow inside the model by a hot-wire smoke stream method

Combined Radiation-Convection in Gray Fluids Enclosed in Vertical Cavities

The interaction of thermal radiation with natural convection in a gray fluid contained inside a cavity is numerically examined. The radiation part of the problem is treated by using the two-dimensional P-1 approximation. The effect of radiation on the conduction, transition, and boundary layer regimes is investigated. The results show that radiation decreases the intensity of the flow at low Rayleigh numbers and, in contrast, leads to an increased flow in convection regimes. The influence of the radiative parameters on the flow and heat transfer is discussed.

Combined Radiation Convection in Thermally Developing Poiseuille Flow with Scattering

The solution for thermally developing Poiseuille flow with scattering is obtained by using the method of collocation. The results show that scattering tends to decrease radiation component without affecting the convective component at low optical thicknesses. For moderate to high values of optical thicknesses, both the convective and radiation components are reduced. The relative effect of scattering both on convective and radiation Nusselt numbers appears to be unaffected by a change in the surface emissivity. A significant feature of combined radiation-convection in thermally developing flows appears to be that the total Nusselt number increases downstream of position of minimum rather than approaching an asymptotic value as is the case with corresponding pure convection. Another departure in the behavior appears to be the lack of existence of similarity in the temperature profiles, particularly at low values of conduction-radiation parameter.

Spline Collocation Solution of Combined Radiation-Convection in Thermally Developing Flows with Scattering

Spline Collocation Solution of Combined Radiation-Convection in Thermally Developing Flows with Scattering

Combined Radiation—Convection for a Real Gas

A study of interaction of radiative transfer with convective transfer is presented for slug flow of an absorbing-emitting gas in a circular tube with an isothermal black wall. The zone method of solution is utilized to evaluate axial gas temperature and wall heat flux distributions using recently developed direct exchange areas for arbitrary zone width to radius ratio. Gas radiative properties are evaluated from the weighted sum of gray gases model with weighting factors and gray gas absorption coefficients applicable for an equimolal mixture of carbon dioxide and water vapor. Results are presented for several values of the governing parameters which are the Boltzmann and Stanton numbers, inlet gas and tube wall temperatures, as well as tube length to diameter ratio. Effects of cooling and heating of the gas are examined.