Particles temperature sensitivity

Commercial Fischer-Tropsch processes have been based exclusively on gas-particle operations, mainly in fixed beds (P2). The chemical reactions are highly exothermic, however, and accurate temperature control is therefore difficult to achieve in a fixed bed. Good temperature control is important because of the temperature sensitivity of the chemical reactions taking place, and several attempts have therefore been made to develop processes based on other types of operation. 

At low temperatures, reaction towards N2 and N2O product formation preferentially occurs at the (100) surface, and hence a significant particle shape sensitivity is predicted. At higher temperatures when NO readily desorbs, overall activation barriers on the different surfaces tend to become similar and hence surface sensitivity becomes less. The high selectivity toward NO at higher temperatures relates... 

As the gel is very dilute, the temperature sensitivity in this region is likely related to the increased Brownian motion which breaks the weakly bonded structure into discrete floes. However, whether this occurs as a result of changes of particle charge and potential and/or dehydration of the dispersed phase is unknown at this time (19). 

Fig. 7.19 shows the burning rates of AP-HTPB composite propellants at 243 K and 343 K. The propellants are composed of bimodal fine or coarse AP particles. The chemical composihons of the propellants are shown in Table 7.2. The burning rates of both propellants are seen to increase linearly in an In r versus In p plot in the pressure range 1.5-5 MPa, and also increase with increasing initial propellant temperature at constant pressure.Ii l The burning rate increases and the temperature sensitivity decreases with decreasing AP particle size. 

Fig. 7.20 shows the effect of an added catalyst on the burning rates of propellants composed of fine or coarse AP particles. The added catalyst is 2,2-bis(ethylferro-cenyl)propane (BEEP). The burning rates of both propellants are seen to be increased significantly by the addition of 1.0% BEFP. BEFP has a more pronounced effect on the burning rate of the propellant composed of fine AP particles than on that of the propellant composed of coarse AP particles. The temperature sensitivity of the propellant composed of fine AP particles with 1.0% BEFP is lower than that of the propellant composed of coarse AP particles with 1.0% BEFP. 

Fig. 7.19 Burning rates and their temperature sensitivity for AP-HTPB composite propellants composed of fine or coarse AP particles.

The relationship between temperature sensitivity and burning rate is shown in Fig. 7.21 as a function of AP particle size and burning rate catalyst (BEFP).li31 The temperature sensitivity decreases when the burning rate is increased, either by the addition of fine AP particles or by the addition of BEFP. The results of the temperature sensitivity analysis shown in Fig. 7.22 indicate that the temperature sensitivity of the condensed phase, W, defined in Eq. (3.80), is higher than that of the gas phase, 5), defined in Eq. (3.79). In addition, 4> becomes very small when the propel-... 

When these oxidizer particles are mixed with a binder such as HTPB, a nitropoly-mer, or GAP, the burning rate decreases with increasing mass fraction of ADN or HNF particles.[3+l Though the temperature sensitivity of an ADN composite propellant is significantly high in the low-pressure region, 0.005 at 1 MPa, it decreases... 

When HNF or ADN particles are mixed with a GAP copolymer containing aluminum particles, HNF-GAP and ADN-GAP composite propellants are formed, respectively. A higher theoretical specific impulse is obtained as compared to those of aluminized AP-HTPB composite propellants.However, the ballistic properties of ADN, HNIW, and HNF composite propellants, such as pressure exponent, temperature sensitivity, combustion instability, and mechanical properties, still need to be improved if they are to be used as rocket propellants. 

The results of the calculations are shown in Fig. 8.4. The assumed values for the physical constants and reaction kinetics are listed in Ref [1]. The burning rate increases with increasing pressure, and also increases with increasing concentration and decreasing particle size of the AP particles. These calculated results compare favorably with the experimental results shown in Fig. 8.4. The calculated burning surface temperature of the DB matrix varies from 621 K at 1 MPa to 673 K at 8 MPa. The temperature sensitivity decreases with increasing pressure (a = 0.0056 K at 8 MPa).[i]... 

If this ratio is greater than 1.0, no sensitization by the grit particle results, but if it is less than 1.0, the grit particle effectively sensitizes the explosive because it allows the formation of hot spots of higher temperature than those created in the pure explosive (Ref 23, p 180)... 

In the presence of tunieamycin, cells infected with Rous sarcoma virus produced virus particles that lacked infectivity, and were devoid of the envelope glycoproteins gp85 and gp35. Virus particles lacking envelope glycoproteins had previously been found in a deletion mutant of Rous sarcoma virus and in a temperature-sensitive mutant of... 

In contrast, the interwell time t(ct) is very temperature-sensitive and might change virtually unboundedly in a sufficiently narrow temperature interval. [Note that under constant particle volume the parameter a according to its definition (4.75) may be treated as the inverse temperature.] Qualitatively, the behavior of t(ct) is as follows. At low potential barriers (a [Pg.555]

It is a well-known fact that, as the size of a metal particle is decreased, the overlap of the bands of valence electrons, with which we are mainly concerned, diminishes, and finally they are replaced by discrete energy levels characteristic of the isolated atom. This results in the loss of electrical conductivity and in the Mie plasmon resonance, an effect that has been noted with the AU55 and smaller clusters, on the basis of which they were described above as being molecular . The extent of band overlap is temperature-sensitive because of thermal excitation, i.e. bands tend to convert to levels as temperature falls thus metallic properties may be seen at high temperature and insulator properties at low temperature. As an approximate guide we may take the relation... 

Cationic PNIPAM-covered magnetic particles Hetero coagulation of iron oxide nanoparticles onto cationic particles. Encapsulation of preformed particles by polymerization of NIPAM, BAM and AEMH 300-1000 nm Superparamag-netic, bioreactive particles. Temperature, salinity and pH sensitive [10,18,19]... 

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