Energy flux rate

Since the absorption spectrum is a ratio it is amenable to other interpretations. One such interpretation is that the absorption spectrum is the ratio of energy absorbed to energy incident. From this perspective, the quantity /)co(d/d0< li 0l f 0) is interpreted as the rate of energy absorption (per unit volume), since d E/d t = /)co(d AVd t) while tire quantity E dha is interpreted as the incident energy flux, which depends only on the field intensity and is independent of frequency. 

Here t. is the intrinsic lifetime of tire excitation residing on molecule (i.e. tire fluorescence lifetime one would observe for tire isolated molecule), is tire pairwise energy transfer rate and F. is tire rate of excitation of tire molecule by the external source (tire photon flux multiplied by tire absorjDtion cross section). The master equation system (C3.4.4) allows one to calculate tire complete dynamics of energy migration between all molecules in an ensemble, but tire computation can become quite complicated if tire number of molecules is large. Moreover, it is commonly tire case that tire ensemble contains molecules of two, tliree or more spectral types, and experimentally it is practically impossible to distinguish tire contributions of individual molecules from each spectral pool. 

The nonconvective energy flux across the boundary is composed of two terms a heat flux and a work term. The work term in turn is composed of two terms useful work deflvered outside the fluid, and work done by the fluid inside the control volume B on fluid outside the control volume B, the so-called flow work. The latter may be evaluated by imagining a differential surface moving with the fluid which at time 2ero coincides with a differential element of the surface, S. During the time dt the differential surface sweeps out a volume V cosdSdt and does work on the fluid outside at a rate of PV cos dS. The total flow work done on the fluid outside B by the fluid inside B is... 

Radiated energy flux Energy flux to a black body Flow rate... 

Irradiation G Total thermal radiation energy incident on a surface per unit time per unit area Irradiation (G), and Radiosity J) are all energy fluxes (i.e., rate... 

Figure 2. The Radiant Panel Test was designed to measure both critical ignition energy and rate of heat release. A sample is mounted facing a controlled heat flux but at a 3CP angle to it such that the upper part of the specimen is more severely exposed. Since irradiance decreases down the specimen, the time progress of ignition down the specimen serves to measure central ignition energy. Thermocouples in the stack above the specimen serve as a measure of heat release rate.

For the second item ignition to lead to flashover, the area involved must equal or exceed the total critical area needed for the second item. The time for ignition depends inversely on the exposure heat flux (Equation (11.51)). Figure 11.21 shows the behavior for ignition of the second item, where Af,i is the fixed area of the first item and AF c is the critical area needed. The energy release rate of both fuels controls the size of the jump at criticality and depends directly on AFAhc/L. No flashover will occur if the jump in energy for the second item is not sufficient to reach the critical area of fuel, AFjc- The time to achieve the jump or to attain flashover is directly related to the fuel property,... 

Fig. 1. The organic polymer etching rate is a linear function of the bombardment energy flux as determined by Visser and de Vries [29] (triangles) and by Jurgensen and Rammelsberg [34] (squares).

Fig. 2. The organic polymer 02 RIE rate (filled points) tracks the bombardment energy flux (open points) as the pressure is varied at a constant 500 V self bias, and at 13.5 MHz.

From this definition, it can be observed that T,(k. t) is the net rate at which turbulent kinetic energy is transferred from wavenumbers less than k to wavenumbers greater than k. In fully developed turbulent flow, the net flux of turbulent kinetic energy is from large to small scales. Thus, the stationary spectral energy transfer rate Tu(k) will be positive at spectral equilibrium. Moreover, by definition of the inertial range, the net rate of transfer through wavenumbers /cei and kdi will be identical in a fully developed turbulent flow, and thus... 

We have already used in the examples most of the laws governing the transfer of energy, mass, and momentum. These transport laws all have the form of a flux (rate of transfer per unit area) beiivc proportional to a driving force (a gradient in temperature, concentration, or v whty). The proportionality constant is a physical property of the system (like thermal conduetivity, diffiisivity, or viscosity). 

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