Stefan constant

The total energy radiated per unit surface area of a black body in unit time is proportional to the fourth power of its thermodynamic temperature. The constant of proportionality, the Stefan constant (or Stefan-Boltzmann constant) has the value 5.6697 X 10-8 J g-i jji-2 K". The law was discovered by Joseph Stefan (1853-93) and theoretically derived by Ludwig Boltzmann. 

Boltzmaim showed that the energy density emided per second from a unit surface of a black body is a7 where T is the temperature and a is the Stefan-Boltzmaim constant, but it takes statistical mechanics to produce the fonnula... 

Spectral bandwidth of excita- Stefan-Boltzmann constant a... 

Design Methods for Calciners In indirect-heated calciners, heat transfer is primarily by radiation from the cyhnder wall to the solids bed. The thermal efficiency ranges from 30 to 65 percent. By utilization of the furnace exhaust gases for preheated combustion air, steam produc tion, or heat for other process steps, the thermal efficiency can be increased considerably. The limiting factors in heat transmission he in the conductivity and radiation constants of the shell metal and solids bed. If the characteristics of these are known, equipment may be accurately sized by employing the Stefan-Boltzmann radiation equation. Apparent heat-transfer coefficients will range from 17 J/(m s K) in low-temperature operations to 8.5 J/(m s K) in high-temperature processes. 

Here, Qr is the energy loss per second by a surface at temperature to its suiToundings at temperature T, , the emissivity of the subsU ate being e, the view factor F being the fraction of tire emitted radiation which is absorbed by the cool sunoundings, and a being tire Stefan-Boltzmairn radiation constant (5.67 X 10 Jm s In the present case, tire emissivity will have a value of about 0.2-0.3 for the metallic subsU ates, but nearly unity for the non-metals. The view factor can be assumed to have a value of unity in the normal situation where the hot subsU ate is enclosed in a cooled container. 

Tj is the surface temperature of the panel, Tj, the thermometer bulb temperature, Tj the air temperature, and T the temperature of the walls of the building. F is the view factor from the bulb to the heating panel, e is the emissivity of the thermometer bulb at temperature T cr is the Stefan-Boltzmann constant (5.67 X 10 W m K " ), and is the convective heat transfer coefficient from bulb to air. 

Here a is the Stefan-Boltzmann constant, n the refractive index, and the absorption coefficient. 

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