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.

Simultaneous effects of nonlinear thermal radiation and Joule heating on the flow of Williamson nanofluid with entropy generation

Abstract: The present communication addresses the heat and mass transfer mechanism in MHD nanofluid flow of Williamson fluid over a stretching sheet taking the combined effects of Joule heating, nonlinear thermal radiation and viscous dissipation into consideration. For physical relevance we also analyzed the influence of chemical reactions on the flow field. The appropriate transformations are implemented to metamorphose the governing PDEs into a set of coupled ODEs. The shooting technique along with fourth order Runge–Kutta method has been implemented to get the solutions of obtained highly non-linear ODEs. The second law of thermodynamics is implemented to model the equation of entropy generation for the current analysis. Impact of different dominant parameters on velocity, temperature, concentration, entropy generation as well as Bejan number are described through graphs whereas the variation in the skin friction coefficient, heat transfer rate and mass transfer rate are studied using numerical data in the tabular form. It is observed from the obtained numerical data that the rate of heat transfer gets reduced with increase in Eckert number while the thermal radiation parameter tends to enhance it. Increase in Brinkman parameter leads to a rise in entropy generation while it (Brinkman parameter) has an adverse effect on Bejan number.

Thermal diffusivity measurements in opaque solids by the mirage technique in the temperature range from 300 to 1000 K

Abstract: A method to measure the thermal diffusivity of solid samples as a function of temperature is presented. The measurement technique is based on the mirage effect and in its linear zero‐crossing relation for the transverse deflection, whose slope directly gives the diffusivity of the material. A 3D theoretical model has been developed in order to include both the effects of the radiative and convective heat transfers between the sample and its surroundings, and the temperature dependence of the refractive index and thermal diffusivity of the gas. The model also incorporates the effects introduced by the mirage parameters (sizes of the pump and probe beams, and probe beam height). The samples studied are opaque and thermally thick, and the applicability of the method is restricted to materials with diffusivity ≳1 mm2/s. Two experimental mirage setups are presented, one with the sample being heated in an open environment, and the other with the sample heated within a furnace. In the first case the range of measurable temperatures goes from ambient to ∼500 K, whereas in the second the upper limit is ∼1000 K. A comparison of the experimental results obtained with this method with those from the literature on calibrated samples of pure nickel, pure cobalt, and an AISI‐302 alloy of low thermal diffusivity, confirm the validity of the model and method proposed.

A numerical study of unsteady non-Newtonian Powell-Eyring nanofluid flow over a shrinking sheet with heat generation and thermal radiation

Abstract: In this paper we investigate the unsteady boundary-layer flow of an incompressible Powell-Eyring nanofluid over a shrinking surface. The effects of heat generation and thermal radiation on the fluid flow are taken into account. Numerical solutions of the nonlinear differential equations that describe the transport processes are obtained using a multi-domain bivariate spectral quasilinearization method. This innovative technique involves coupling bivariate Lagrange interpolation with quasilinearization. The solutions of the resulting system of equations are then obtained in a piecewise manner in a sequence of multiple intervals using the Chebyshev spectral collocation method. A parametric study shows how various parameters influence the flow and heat transfer processes. The validation of the results, and the method used here, has been achieved through a comparison of the current results with previously published results for selected parameter values. In general, an excellent agreement is observed. The results from this study show that the fluid parameters e and δ reduce the flow velocity and the momentum boundary-layer thickness. The heat generation and thermal radiation parameters are found to enhance both the temperature and thermal boundary-layer thicknesses.