Heat Transfer: Radiation

These flashcards cover key vocabulary and concepts related to thermal radiation, including definitions and principles central to understanding radiation heat transfer.

Thermal Radiation

Heat transfer that does not require a material medium to occur, can happen in a vacuum.

Blackbody

An idealized physical body that absorbs all incident radiation and emits the maximum possible radiation at a given temperature.

Emissivity (ε)

The measure of how efficiently a real surface emits energy relative to a blackbody, with values ranging from 0 to 1.

Absorptivity (α)

The fraction of radiation absorbed by a surface, varies between 0 and 1.

Reflectivity (ρ)

The fraction of radiation that is reflected by a surface.

Transmissivity (τ)

The fraction of radiation transmitted through a surface.

View Factor

A geometric parameter that defines the fraction of radiation leaving one surface that strikes another surface.

Reciprocity Relation

A principle that relates the view factors between two surfaces based on their geometric areas.

Summation Rule

The principle that the sum of view factors from a surface to all surfaces in an enclosure must equal one.

Stefan-Boltzmann Law

The law stating that the emission of thermal radiation is proportional to the fourth power of the absolute temperature.

Irradiation (G)

The rate at which incident radiation is received on a unit area of a surface.

Radiant Heat Transfer

The transfer of heat energy through the emission and absorption of electromagnetic radiation.

Gray Surface

A surface that has properties that are independent of wavelength, often used in radiation transfer analyses.

Volumetric Phenomenon

A description of radiation being emitted throughout the entire volume of a substance, especially fluids.

Thermal Equilibrium

The state in which two objects in thermal contact no longer exchange heat; their temperatures equalize.