Distributed heat release

The physics and modeling of turbulent flows are affected by combustion through the production of density variations, buoyancy effects, dilation due to heat release, molecular transport, and instabiUty (1,2,3,5,8). Consequently, the conservation equations need to be modified to take these effects into account. This modification is achieved by the use of statistical quantities in the conservation equations. For example, because of the variations and fluctuations in the density that occur in turbulent combustion flows, density weighted mean values, or Favre mean values, are used for velocity components, mass fractions, enthalpy, and temperature. The turbulent diffusion flame can also be treated in terms of a probabiUty distribution function (pdf), the shape of which is assumed to be known a priori (1). 

Calculated heat release distributions for total spark energy of 0.7mJ at 500 ps. (a) Ratio of capacity spark energy 20%. (b) Ratio of capacity spark energy 80%. 

The previous expression can also be derived by starting from the wave equation for the pressure in the presence of a distribution of heat release ... 

Cylinders have the advantage that they are cheap to manufacture. In addition to varying the shape, the distribution of the active material within the pellets can be varied, as illustrated in Figure 6.7. For packed-bed reactors, the size and shape of the pellets and the distribution of active material within the pellets can be varied through the length of the reactor to control the rate of heat release (for exothermic reactions) or heat input (for endothermic reactions). This involves creating different zones in the reactor, each with its own catalyst designs. 

Figures 4.6—4.8 are the results for the stoichiometric propane-air flame. Figure 4.6 reports the variance of the major species, temperature, and heat release Figure 4.7 reports the major stable propane fragment distribution due to the proceeding reactions and Figure 4.8 shows the radical and formaldehyde distributions—all as a function of a spatial distance through the flame wave. As stated, the total wave thickness is chosen from the point at which one of the reactant mole fractions begins to decay to the point at which the heat release rate begins to taper off sharply. Since the point of initial reactant decay corresponds closely to the initial perceptive rise in temperature, the initial thermoneutral period is quite short. The heat release rate curve would ordinarily drop to zero sharply except that the recombination of the radicals in the burned gas zone contribute some energy. The choice of the position that separates the preheat zone and the reaction zone has been made to account for the slight exothermicity of the fuel attack reactions by radicals which have diffused into...

Distribution of extinguishing agent to absorb heat released of decrease the heat release rate... 

The experimental studies show that heating accelerates the flow and arrests jet growth absolute values of turbulence intensity increase but not as rapidly as the mean velocities. So, normalized turbulence intensities are lower. The effects of the amount of heating and its distribution on the evolution of the computed jet have been previously reported in [7]. These results show all the qualitative features that have been found in the experiments. In this paper, the findings of the study related to the effects of heat release on the vortical structure and entrainment characteristics of the jet are described. 

Since G and Ch appear only as a product, G = GCh is used as the relevant nondimensional parameter governing heat release in the present studies. The other governing parameters for this flow are Re and Pr, along with the precise strength and distribution of the source term in the energy equation. 

The needle valve oscillated up to 12% of the total fuel, and flow rates larger than around 3% of the total implied that the bulk mean velocity in the axial jet was greater than the bulk flow in the swirler and the mean equivalence ratio was greater than unity. It was found that the amplitude of oscillations was unaffected by values of bulk mean velocity of the axial jet greater than 2.5 times that in the swirler for a main flow swirl number of 1.35, and 4 times that value for a swirl number of 0.6. Larger values of axial jet velocity led to a decrease in amplitude due to the penetration of the swirl-induced recirculation region by the jet and the consequences for the distribution of heat release. 

Using GRI-Mech (GRIM30. mec), determine the temperature and species distributions for a freely propagating, stoichiometric, methane-air, mixture at a pressure of 10 Torr. From the solution determine the volumetric heat-release-rate profile through the thickness of the flame. 

With respect to heat released to the immediate surroundings, the temperature distribution from the surface of Au nanoparticles has been calculated using a simple heat transfer model.75,76 The local temperature increase AT(r) around a single nano-particle is described as ... 

The concepts discussed so far indicate that the major challenge in asymmetric operation is correct adjustment of the loci of heat release and heat consumption. A reactor concept aiming at an optimum distribution of the process heat has been proposed [25, 26] for coupling methane steam reforming and methane combustion. The primary task in this context is to define a favorable initial state and to assess the distribution of heat extraction from the fixed bed during the endothermic semicycle. An optimal initial state features cold ends and an extended temperature plateau in the catalytic part of the fixed bed. The downstream heat transfer zone is inert, in order to avoid any back-reaction (Fig. 1.13). 

The simulation program has been extensively used for process optimization studies as it permits accurate prediction of isomer distribution and heat release. It offers theoretical explanations for isomer control practices arrived at through several years of plant operating experience. The model was used in designing laboratory experiments to study mass transfer under various process conditions and reactor configuration. Since mass transfer and chemical kinetics are simultaneously important in this process, a model is necessary to "filter out" the kinetics effects for mass transfer correlations. The results of our laboratory studies will be presented in future papers. 

In this paper, the chemical adsorption of NH3, using pulses, has been studied by combining the results of calorimetric measurement of heat released (in a differential scanning calorimeter) with the measurement of desorbed amount of base (by FTIR analysis of desorbed gases). In this way, the differential adsorption heat, representative of the aridity strength distribution of the deactivated catalyst, is obtained and the restrictions inherent to other techniques, which are affected by the measurement of coke degradation products, are avoided. 

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