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.

Thermodynamic limits of energy harvesting from outgoing thermal radiation.

Abstract: We derive the thermodynamic limits of harvesting power from the outgoing thermal radiation from the ambient to the cold outer space. The derivations are based on a duality relation between thermal engines that harvest solar radiation and those that harvest outgoing thermal radiation. In particular, we derive the ultimate limit for harvesting outgoing thermal radiation, which is analogous to the Landsberg limit for solar energy harvesting, and show that the ultimate limit far exceeds what was previously thought to be possible. As an extension of our work, we also derive the ultimate limit of efficiency of thermophotovoltaic systems.

A comparative entropy based analysis of Cu and Fe3O4/methanol Powell-Eyring nanofluid in solar thermal collectors subjected to thermal radiation, variable thermal conductivity and impact of different nanoparticles shape

Abstract: The efficiency of any nanofluid based thermal solar system depend on the thermophysical properties of the operating fluids, type and shape of nanoparticles, nanoparticles volumetric concentration in the base fluid and the geometry/length of the system in which fluid is flowing. The recent research in the field of thermal solar energy has been focused to increase the efficiency of solar thermal collector systems. In the present research a simplified mathematical model is studied for inclusion in the thermal solar systems with the aim to improve the overall efficiency of the system. The flow of Powell-Eyring nanofluid is induced by non-uniform stretching of porous horizontal surface with fluid occupying a space over the surface. The thermal conductivity of the nanofluid is to vary as a linear function of temperature and the thermal radiation is to travel a short distance in the optically thick nanofluid. Numerical scheme of Keller box is implemented on the system of nonlinear ordinary differential equations, which are resultant after application of similarity transformation to governing nonlinear partial differential equations. The impact of non dimensional physical parameters appearing in the system have been observed on velocity and temperature profiles along with the entropy of the system. The velocity gradient (skin friction coefficient) and the strength of convective heat exchange (Nusselt number) are also investigated.

Classical statistical thermodynamics and electromagnetic zero point radiation

Abstract: Classical statistical thermodynamics in the presence of electromagnetic radiation is reanalyzed, and is reformulated to give a natural classical description of the phenomena which originally led to the introduction of the idea of quanta. The traditional classical ideal gas fails to exist in principle for particles of finite mass which have electromagnetic interactions, and hence the classical proofs of energy equipartition are all erroneous. A consistently classical treatment of thermal radiation leads to the natural introduction of temperature-independent fluctuating radiation in the universe. The spectrum of this electromagnetic zero-point radiation may be obtained from the arguments for Wien's displacement law or from the requirement of Lorentz invariance of the radiation spectrum; this zero-point spectrum agrees with the $\frac{1}{2}\ensuremath{\hbar}\ensuremath{\omega}$ per normal mode familiar in quantum theory. The presence of temperature-independent disordered energy from zero-point radiation leads to a contribution to the entropy connected with thermodynamic probability distinct from the contribution of caloric entropy. The use of quanta in calculations of the thermodynamic probability is seen as a subterfuge to account for this mismatch between caloric entropy and probability. Several examples of statistical thermodynamics, which are generally regarded as having their explanation in terms of quanta, allow natural explanations within the context of classical theory with classical electromagnetic zero-point radiation.

Effective Thermal Conductivities in Packed Beds

Abstract: Electric analogue circuits are used for evaluating the effective thermal conductivities in packed beds without fluid flow, taking into consideration the numbers of packings placed in the direction of heat flow.In the analysis, it is assumed that the thermal resistance within packed beds may occur in the following forms:(1) Thermal resistance of packing itself.(2) Thermal resistance of contact area.(3) Thermal resistance of fluid between packings.(4) Thermal resistance to heat radiation from packing to packing.(5) Thermal resistance to heat radiation from packing to adjoining packing beyond one.The equations obtained are given in the form of Eqs. 1, 3, 6 and 7. Introducing the values of thermal resistance into Eq. 7, we have obtained Eq, 8 which expresses the relation of ks/kg.Experiments have been carried out with various packings: iron, porcelain, glass balls and insulating fire bricks at the temperature between 100 and 1000°C.Comparisons between the experimental results and the values obtained from Eq. 8 are shown in Figs. 11, 12, 13, 14 and 15. The calculation can be readily handled by employing the chart of Fig. 8, without using the complicated formula, Eq. 8. The difference between the value obtained from the chart (Fig. 8) and that obtained from Eq. 8 is small and negligible.