Energy Transfers by Radiation

Abdelhanine Benallou

• Publisher: Wiley-ISTE
• Year: 2019
• Print ISBN: 9781786302779
• eBook ISBN: 9781119629443
• Edition: 1
• Topic: Ciencias físicas
• Subtopic: Termodinámica

Inside industrial furnaces and combustion chambers, energy is essentially exchanged by radiation. It is through the same mechanism that the energy emitted by the Sun spreads through different media to reach the Earth. Developing a sound understanding of the laws underlying energy exchanges by radiation is therefore essential, not only for establishing design equations for industrial equipment, but also for an optimal harvesting of solar energy and a better understanding of climate change phenomena such as the greenhouse effect. Energy Transfers by Radiation establishes the basic laws and equations which support the quantification of energy fluxes transferred between surfaces for situations similar to those usually encountered in industrial processes or in solar energy applications.

1
Origin of Radiation

1.1. Introduction

The origin of radiation is almost as old as the history of the creation of matter. Its essence finds itself combined with that of matter and electromagnetic waves originating far back in the Big Bang. Indeed, according to the Big Bang model, presented in the form of a light-hearted summary in a reader-friendly article (Lachiezo-Rey, 2016), the first particles (quarks) assembled to form protons and neutrons. Then, this assembly process continued to form the first atomic nuclei. This is known as primordial nucleosynthesis.

It enabled the development of the simplest atomic nuclei: hydrogen (1 proton), deuterium (proton + 1 neutron), helium (2 protons + 2 neutrons) and lithium (3 protons and 4 neutrons). All other nuclei known to us today as constituting matter would be formed later.

In ionized gas state, this matter emits electromagnetic waves that will be received by the rest of the matter. These energy exchanges between matter and electromagnetic waves form the basis of processes that allowed other nuclei to develop, resulting in the composition of matter that we know today.

The origin of radiation is thus found confined in infinitesimal matter.

The work conducted by Max Planck (1858–1947), Niels Bohr (1885–1962) and Albert Einstein offers a model that allows us to trace back to the corpuscular origin of radiation. Indeed, interactions between radiation and matter, first demonstrated by Max Planck, showed that exchanges between electromagnetic radiation and matter can only occur in bundles, having specific energies that depend on the matter considered. He referred to these bundles as quanta and so quantum mechanics was born.

Albert Einstein would later conclude that these quanta are carried by particles: photons. He also asserted that these photons move at the speed of light and that they convey energy which is characterized by a wave of length λ, well defined by the matter considered.

Niels Bohr’s atomic model came to complete this representation of radiation-matter interactions.

1.2. The Niels Bohr model

In Bohr’s model, an atom can only exist in certain energy states. Each of these states is defined by a specifically-determined energy level. The transition from an initial state, defined by energy level E_i, to a final state (E_F) can only take place with a radiation of energy E_R, such that:

Thus (see Figure 1.1), the transition of an atom from an excited state (E_E) to a less excited state (E_M) leads to the emission of a photon, the energy (hν) of which is such that:

Figure 1.1. Radiation emission by de-excitation of an atom. For a color version of this figure, see www.iste.co.uk/benallou/energy4.zip

Conversely, the absorption of a photon of energy hν by an atom that is at initial energy level, E_i, returns it to an excited state, E_E, such that (see Figure 1.2):

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Table of contents

• Cover
• Table of Contents
• Preface
• Introduction
• 1 Origin of Radiation
• 2 Magnitudes Used in Radiation
• 3 Analysis of Radiative Energy Transfers: Black-body Radiation
• 4 Radiant Properties of Real Surfaces
• 5 Radiation Balances between Real Surfaces Separated by a Transparent Medium
• 6 Practical Determination of Shape Factors
• 7 Balances of Radiative Energy Transfers between Black Surfaces
• 8 Balances on Radiative Energy Transfers between Gray Surfaces
• 9 Electrical Analogies in Radiation
• 10 Reduction of Radiating Energy Transfers through Filtering
• 11 Radiative Energy Transfers in Semi-transparent Media
• 12 Exercises and Solutions
• Appendix: Database
• References
• Index
• End User License Agreement