Thermal radiation

About: Thermal radiation is a research topic. Over the lifetime, 12290 publications have been published within this topic receiving 197186 citations. The topic is also known as: heat radiation.

Coupled fire dynamics and thermal response of complex building structures

Abstract: Simulation of the effects of severe fires on the structural integrity of buildings requires a close coupling between the gas phase energy release and transport phenomena, and the stress analysis in the load-bearing materials. The connection between the two is established primarily through the interaction of the radiative heat transfer between the solid and gas phases with the conduction of heat through the structural elements. This process is made difficult in large, geometrically complex buildings by the wide disparity in length and time scales that must be accounted for in the simulations. A procedure for overcoming these difficulties used in the analysis of the collapse of the World Trade Center towers is presented. The large scale temperature and other thermophysical properties in the gas phase are predicted using the NIST Fire Dynamics Simulator. Heat transfer to subgrid scale structural elements is calculated using a simple radiative transport model that assumes the compartment is locally divided into a hot, soot laden upper layer and a cool relatively clear lower layer. The properties of the two layers are extracted from temporal averages of the results obtained from the Fire Dynamics Simulator. Explicit formulae for the heat flux are obtained as a function of temperature, hot layer depth, soot concentration, and orientation of each structural element. These formulae are used to generate realistic thermal boundary conditions for a coupled transient three-dimensional finite element code. This code is used to generate solutions for the heating of complex structural assemblies.

Validity of Kirchhoff's law for semitransparent films made of anisotropic materials

Abstract: Kirchhoff's law relates the emittance and absorptance of an object and has played an important role in radiative heat transfer calculations for many engineering applications. Along with the advancement of metamaterials, two-dimensional materials, and micro/nanoscale thermal radiation, Kirchhoff's law has been revisited by several groups. Some studies also questioned the derivations and applicability of the statement of Kirchhoff's law that appears in prevalent radiative heat transfer textbooks. The present study begins with a short review of Kirchhoff's law for isotropic objects and its validity for both hemispherical emittance and directional emittance. Then, this study formulates Kirchhoff's law for opaque anisotropic materials, considering both co-polarization and cross-polarization, and then for semitransparent films. It is shown that for macroscopic objects, as long as the Helmholtz reciprocity can be established, conventional expressions of Kirchhoff's law can be applied for engineering thermal analysis and design even with anisotropic media and metamaterials. Numerical examples and results are provided, based on a natural hyperbolic material and a magneto-optical material, to illustrate the reciprocity and applicability of Kirchhoff's law.

Unsteady MHD Flow of Nanofluid with Variable Properties over a Stretching Sheet in the Presence of Thermal Radiation and Chemical Reaction

Abstract: The unsteady magnetohydrodynamics (MHD) flow of nanofluid with variable fluid properties over an inclined stretching sheet in the presence of thermal radiation and chemical reaction is studied taking into account the effect of variable fluid properties in thermal conductivity and diffusion coefficient. The governing partial differential equations are transformed into ordinary differential equations by using similarity transformation. The numerical solutions of the problem are obtained by using the fourth order Runge-Kutta method in line with the shooting technique. It is found that the increase in both thermal conductivity and radiative heat flux decreases the heat transfer rate but increases the skin friction and mass transfer rates. It is further observed that the increase in porosity parameter and magnetic field reduces the skin friction, heat, and mass transfer rates.

Exploring the impact of magnetic dipole on the radiative nanofluid flow over a stretching sheet by means of KKL model

Abstract: This study mainly focusses on the rheological properties of the nanofluids by using Koo–Kleinstreuer–Li model. The nanofluids have been proposed as viable replacements to traditional fluids due to their increased heat transport capacity. In this regard, the influence of non-uniform heat sink/source and thermal radiation effects on the nanoliquid flow past a stretching sheet is studied in the presence of chemical reaction and magnetic dipole. The defined flow equations are transformed to ordinary differential equations by using appropriate similarity variables and then they are numerically tackled with Runge Kutta Fehlberg-45 (RKF-45) scheme by adopting shooting process. The graphical outcomes of the velocity, thermal, concentration profiles, drag force, Sherwood number and Nusselt number are found to get an obvious insight into the existing boundary layer flow problem. The outcomes reveal that, the gain in values of radiation parameter improves the thermal profile due to the production of inner heat. The rise in Biot number improves the thermal boundary layer region which automatically boosts up the thermal profile. Further, the escalation in space-dependent internal heat sink/source parameter deteriorates the rate of heat transfer.