Power density, 310

The extremely high peak power densities available ia particle beams and lasers can heat the small amounts of matter ia the fuel capsules to the temperatures required for fusion. In order to attain such temperatures, however, the mass of the fuel capsules must be kept quite low. As a result, the capsules are quite small. Typical dimensions are less than 1 mm. Fuel capsules ia reactors could be larger (up to 1 cm) because of the iacreased driver energies available. 

The integral of the temperature gradient of the spectral power density from wavelength Xl to X2, is readily calculable using the Planck radiation law (5). Constant emissivity is assumed for equation 3. 

Fig. 4. Automotive shaft cross sections showing the effect of power density vs hardened depth.

Blackbody Emittance. Representative blackbody emittance (9,10), calculated as a power spectral density, is shown in Figure 2. The wavelength, X, of peak power density for a blackbody at temperature, T, is given by Wien s displacement law  

Luminance is the luminous intensity divided by the area of emission of light (Iumens/steradian/m2). This is the power density emitted per unit area. 

A second property, closely related to the first, is the abiHty of the heat pipe to effect heat-flux transformation. As long as the total heat flow is ia equiHbrium, the fluid streams connecting the evaporatiag and condensing regions essentially are unaffected by the local power densities ia these two 

A unique capability of induction heating is apparent in its abdity to heat the surface of a part to a high temperature whde the interior remains at room temperature. Proper selection of material, high frequency, and high power density can produce a thin surface hardness with a heat unaffected core (3). Figure 4 shows the cross section of a typical automotive shaft heated with 10 kH2 at various power densities. The required hardness depth is selected to 

Spectral discrimination (9) and specific gas detection can be modeled if one assumes the gas absorbs photons of a specific wavelength exponentially with distance into the gas (Beet s law). When the absorption distance is x (cm), the incident it power density at the detector in the spectral band pass is J (W/cm ) and the power density incident on the gas is the gas concentration, C (ppm) is given by  

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