Lecture

Radiative Transfer in Participating Media: Key Concepts and Equations

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In course

ME-465: Advanced heat transfer

The course will deepen the fundamentals of heat transfer. Particular focus will be put on radiative and convective heat transfer, and computational approaches to solve complex, coupled heat transfer problems. ...

Description

This lecture covers the principles of radiative transfer in participating media, focusing on the interactions of radiation with matter. The instructor begins by outlining the course structure and the transition from previous topics to the new focus on radiation and participating media. Key concepts such as the radiative transfer equation (RTE) are introduced, emphasizing the importance of understanding how radiation interacts with media that absorb and scatter light. The lecture explains the phenomena of attenuation due to absorption and scattering, detailing how these processes affect the intensity of radiation as it travels through a medium. The instructor discusses the extinction coefficient, its dependence on various factors, and how it relates to Beer-Lambert's law. The lecture also explores the significance of the scattering phase function and its role in determining the behavior of radiation in different media. Finally, the connection between the radiative transfer equation and energy conservation is established, providing a comprehensive understanding of how radiation contributes to heat transfer in participating media.

Official source

Ontological neighbourhood

Chemistry

Physical chemistry: Spectroscopy

Related concepts (32)

Heat transfer

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer.

Thermal radiation

Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is converted to electromagnetic radiation. All matter with a temperature greater than absolute zero emits thermal radiation. At room temperature, most of the emission is in the infrared (IR) spectrum. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.

Radiative equilibrium

Radiative equilibrium is the condition where the total thermal radiation leaving an object is equal to the total thermal radiation entering it. It is one of the several requirements for thermodynamic equilibrium, but it can occur in the absence of thermodynamic equilibrium. There are various types of radiative equilibrium, which is itself a kind of dynamic equilibrium. Equilibrium, in general, is a state in which opposing forces are balanced, and hence a system does not change in time.

Radiative cooling

In the study of heat transfer, radiative cooling is the process by which a body loses heat by thermal radiation. As Planck's law describes, every physical body spontaneously and continuously emits electromagnetic radiation. Radiative cooling has been applied in various contexts throughout human history, including ice making in India and Iran, heat shields for spacecraft, and in architecture. In 2014, a scientific breakthrough in the use of photonic metamaterials made daytime radiative cooling possible.

Passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zero energy consumption or pollution. Because all materials in nature absorb more heat during the day than at night, PDRC surfaces are designed to be high in solar reflectance (to minimize heat gain) and strong in longwave infrared (LWIR) thermal radiation heat transfer through the atmosphere's infrared window (8–13 μm) to cool temperatures during the daytime.

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