Surface power density

The power density distribution referred to in the physics of contained or abgebbarer power to a certain size and consequently always has the shape

As power density, depending on the application, different physical quantities referred to:

• Surface power densities: For transport and flow processes power per unit area sizes with the unit W/m2 be used. These include, as a general size, the intensity I, as a special sizes electromagnetic power density S and Poynting vector irradiance E, ​​emittance M, heat flux q, ψ energy flux density and sound intensity I.
• Volume power density: If the service is based on the volume in which it is implemented, the size has the dimension W/m3 and can φ as volume-related performance or volumetric power density are known. This size is particularly important for technical energy converters ( also with the extent of energy saving, there in addition to the energy density ) of interest, for example in steam boilers, reactors, or batteries.
• Mass power density: The performance can also in particular for the characterization of energy converters and storing, based on the weight, the power density can be thus expressed in W / kg. Special designations are specific performance or gravimetric power density. This size is particularly relevant for vehicles and mobile devices, and plays about recently in electromobility an essential role.
• Spectral power density: With the distribution of power oscillation operations within the relevant frequency or wavelength range is often considered. Used for this purpose, for example, in telecommunications, the power spectral density Sν or Sλ that specified for all frequencies or wavelengths constitutes a power density spectrum.

Radiation physics ( surface power density )

In the field of radiation physics (thermal radiation, electromagnetic waves), the power density S is the amount of the Poynting vector. At a point source, the power density increases quadratically with the distance. Finally, the same power must be distributed with increasing distance between an increasing area A. This is also known as free-space loss.

From the power density of the incident wave and the antenna effective area of ​​the shaft can be determined during usage.

Energy converter

In nuclear engineering, the volume power density is a measure of the released in a reactor heat per unit volume dar. Here one expects mostly in the unit kW / l (1000 watts / liter). The unit kW / kgSchwermetall is used for the description of the fuel load. The latter unit is also called specific performance.

In fuel cells, batteries or capacitors, the volumetric power density of the cells determines the size, the mass power density (W / kg ) weight. When this electric mobility plays a significant role. A Ragone diagram relates them to the energy density.

In the solar energy and wind power use an area-related power density is used here is the surface per incident radiant power or the power of the wind that flows through an area. This power density of an energy source indicates how much power is converted in watts per unit area in square meters. The higher this value, the smaller can, for example, a power plant will be designed. Low power density conversely means a higher cost of materials.

Power density in the application of renewable energy

The power density of renewables is mostly based on the area, as

• The part of the renewable energies directly ( solar thermal, photovoltaic, biomass), indirect ( wind) or partial ( shallow geothermal energy ) depends on the global radiation of the sun, is usefully based on the area and
• Even in the deep geothermal energy with respect to the surface makes sense, since this energy is emitted from within the earth over the spherical surface up / out.

Swell

• Physical size style