Excess AP particles

The crihcal mixture raho at which excess AP particles begin to separate is approximately a 30% mixture of 18 pm AP particles within the DB matrix. Thus, the effechve thickness is derived from Eqs. (8.2) and (8.3) as t] = 5 pm with assumed to be unity. 

When some portion of the AP particles contained within an AP composite propellant is replaced with nitramine particles, an AP-nitramine composite propellan-tis formulated. However, the specific impulse is reduced because there is an insufficient supply of oxidizer to the fuel components, i. e., the composition becomes fuel-rich. The adiabatic flame temperature is also reduced as the mass fraction of nitramine is increased. Fig. 7.49 shows the results of theoretical calculations of and Tf for AP-RDX composite propellants as a function of Irdx- Th propellants are composed of jjxpb(0-13) and the chamber pressure is 7.0 MPa with an optimum expansion to 0.1 MPa. Both I p and T)-decrease with increasing Irdx- The molecular mass of the combustion products also decreases with increasing Irdx due to the production of Hj by the decomposition of RDX. It is evident that no excess oxidizer fragments are available to oxidize this H2. 

Since nitramine pyrolants are fuel-rich materials, the flame temperature decreases with increasing hydrocarbon polymer content The polymers act as coolants and generate thermally decomposed fragments as a result of the exothermic heat of the nitramine particles. The major decomposition products of the polymers are H2, HCHO, CH4, and When AP particles are incorporated into nitramine pyrolants, AP-nitramine composite pyrolants are formed. AP particles produce excess oxidizer fragments that oxidize the fuel fragments of the polymers that surround them. Thus, the addition of AP particles to nitramine pyrolants forms stoichiometricaUy balanced products and the combustion temperature increases. 

Pressure Drop. The prediction of pressure drop in fixed beds of adsorbent particles is important. When the pressure loss is too high, cosdy compression may be increased, adsorbent may be fluidized and subject to attrition, or the excessive force may cmsh the particles. As discussed previously, RPSA rehes on pressure drop for separation. Because of the cychc nature of adsorption processes, pressure drop must be calculated for each of the steps of the cycle. The most commonly used pressure drop equations for fixed beds of adsorbent are those of Ergun (143), Leva (144), and Brownell and co-workers (145). Each of these correlations uses a particle Reynolds number (Re = G///) and friction factor (f) to calculate the pressure drop (AP) per... 

HMX and RDX are energetic materials that produce high-temperature combustion products at about 3000 K. If one assumes that the combustion products at high temperature are HjO, Nj, and CO, rather than COj, both nitramines are considered to be stoichiometricaUy balanced materials and no excess oxidizer or fuel fragments are formed. When HMX or RDX particles are mixed with a polymeric hydrocarbon, a nitramine pyrolant is formed. Each nitramine particle is surrounded by the polymer and hence the physical structure is heterogeneous, similar to that of an AP composite pyrolant... 

When fine aluminum particles are incorporated into AP pyrolants, aluminum oxide (AI2O3) particles are formed when they bum. Dispersal of these aluminum oxide particles in the atmosphere generates white smoke even when the atmosphere is dry. The mass fraction of aluminum particles added is approximately 0.2 for the complete combustion of AP pyrolants. Though an excess of aluminum... 

In addition to the effect of the walls on the drag on the particle, the particle alters the shear on the duct. Consider a particle settling through a quiescent fluid (Fig. 9.1 with Uq = 0). Brenner (B3) showed that, for low particle Re with the particle small by comparison with the distance between particle and wall (i.e., / 1 — where = b/R), there is an excess pressure drop, AP, between points far below and far above the particle given by... 

Finally, the average excess electron density of the hydrated particles over that of the solvent, Ap = p2 — pi, is... 

In deriving Eq. (2.54), it has been assumed that Ap, the potential energy barrier per particle, is weakly temperature-dependent compared with configurational or excess entropy [41,119]. 

Due to preferential scavenging and lateral transport of a daughter radionuclide, the activity of daughter Ap can be greater than that of the parent Ap in sediments. The inputs of daughter radionuclides that are not directly from the in situ decay of the parent (supported) are termed unsupported or excess activity. The unsupported Ap is equal to the supported A ) minus the Ap, as shown in the theoretical radionuclide profiles in figure 7.3. Moreover, the curve for the unsupported Ap decreases with depth more than the supported Ap because it is not being produced in situ from the parent. Consequently, the excess activity of a radionuclide can be used to calculate the time elapsed since the particles with unsupported Ap were last at the surface, relative to a particular depth (A). However, to calculate this it must be assumed that the sedimentation rate and supply of unsupported Ap has remained constant over time. 

In a macroscopic system a supersaturated vapor, Ap = p — Pcoex > 0, is metastable and the excess number of particles will condense into a drop of radius R that consists of the thermodynamically stable liquid. In the framework of classical nucleation theory, the excess free energy of such a spatially inhomogeneous system can be decomposed into a surface and a volume contribution ... 

The two equations, (37) and (38), allow us to calculate the excess free energy as a function of the excess density. To first order we obtain, R Ap and AFdrop = g VAp) with g = 7t/9) / 7. a more accurate expression can be obtained by not condensing all excess particles into the drop but allowing the density, p, of the surrounding vapor to increase [56]. This increases the free energy of the vapor but it decreases the drop s radius and the associated... 

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