Particles thermal

Suhonen, S., Polvinen, R., Valden, M. et al. (2002) Surface oxides on supported Rh particles thermal decomposition of Rh oxide under high vacuum conditions, Appl. Surf. Sci., 200, 48. 

In contrast to the strong effect of gas properties, it has been found that the thermal properties of the solid particles have relatively small effect on the heat transfer coefficient in bubbling fluidized beds. This appears to be counter-intuitive since much of the thermal transport process at the submerged heat transfer surface is presumed to be associated with contact between solid particles and the heat transfer surface. Nevertheless, experimental measurements such as those of Ziegler et al. (1964) indicate that the heat transfer coefficient was essentially independent of particle thermal conductivity and varied only mildly with particle heat capacity. These investigators measured heat transfer coefficients in bubbling fluidized beds of different metallic particles which had essentially the same solid density but varied in thermal conductivity by a factor of nine and in heat capacity by a factor of two. 

Coupling reactions, which are commonly carried out in aqueous media, afford benzimidazolone pigments, usually in the form of hard particles. Thermal after-treatment is necessary to adapt these crude products to the demands of technical application (Sec. 2.2.3). 

The 1.5-nm nanoparticles readily react with thiol or amine-terminated ligands under mild conditions to yield thiol- or amine-stabilized nanoparticles. Triphenylphosphine-stabilized particles thermally decompose with the production of (PPh3)AuCl and metallic gold. 

X Wavelength Wavelength at which the Tpd Particle thermal diffusion time, defined by Eq. (4.50)... 

Km of unity, which implies an isothermal flow. Thus, the flow with a high particle loading and/or a high particle thermal capacity behaves as an isothermal flow because the large heat capacity of the particles significantly offsets the temperature variations in the gas induced by expansion or compression. 

In the emulsion phase/packet model, it is perceived that the resistance to heat transfer lies in a relatively thick emulsion layer adjacent to the heating surface. This approach employs an analogy between a fluidized bed and a liquid medium, which considers the emulsion phase/packets to be the continuous phase. Differences in the various emulsion phase models primarily depend on the way the packet is defined. The presence of the maxima in the h-U curve is attributed to the simultaneous effect of an increase in the frequency of packet replacement and an increase in the fraction of time for which the heat transfer surface is covered by bubbles/voids. This unsteady-state model reaches its limit when the particle thermal time constant is smaller than the particle contact time determined by the replacement rate for small particles. In this case, the heat transfer process can be approximated by a steady-state process. Mickley and Fairbanks (1955) treated the packet as a continuum phase and first recognized the significant role of particle heat transfer since the volumetric heat capacity of the particle is 1,000-fold that of the gas at atmospheric conditions. The transient heat conduction equations are solved for a packet of emulsion swept up to the wall by bubble-induced circulation. The model of Mickley and Fairbanks (1955) is introduced in the following discussion. 

The high energy and shear that result from the movement of the milling media is imparted to the particles as the material is circulated through the milling chamber. The result is the ability to create submicron particles. Thermally labile material is easily handled as the milling chamber is jacketed. By utilizing smaller media (less than 100 p,m) nano-sized (20 nm) particles are achievable. 

Particle thermal conductivity and tube diameter have only marginal effects on the overall heat transfer coefficient within their ranges of variation (kp l-7.5 W/mK dt 21-28 mm). This is apparent in Fig. 5 in the case of tube diameter. 

Keywords Titanium alloy with aluminum and tin Spherical particles Thermal stability Absorbed capacity on hydrogen... 

In addition to molecular weight, thermal FFF is used to measure transport coefficients. For example, the measurement of thermodiffusion coefficients is important for obtaining compositional information on polymer blends and copolymers (see the entry Thermal FFF of Polymers and Particles). Thermal FFF is also used in fundamental studies of thermodiffusion because it is a relatively fast and accurate method for obtaining the Soret coefficient, which is used to quantify the concentration of material in a temperature gradient. However, the accuracy of Soret and thermodiffusion coefficients obtained from thermal FFF experiments depends on properly accounting for several factors that involve temperature. In order to understand the effect of temperature on transport coefficients, as well as the effect on thermal FFF calibration equations, a brief outline of retention theory is given next. 

The stabilizing factors for dispersions are the repulsive surface forces, the particle thermal motion, the hydrodynamic resistance of the medium, and the high surface elasticity of fluid particles and films. 

In this expression, is the thermal conductivity of hydrogen, F is the void fraction, 0 is a flattening coefficient which defines contact quality, is the particle thermal conductivity, and is an expression for the thermal conductivity at the particle-gas-particle interface and includes particle diameter Dp. The effective thermal conductivity is highly influenced by Kp p as it describes the contribution of the fluid to the particle thermal contact quality. For a complete description of the model refer to Rodriguez Sanchez et al. [19]. 

The calculations presented here are consistent with many models and measurements described in the literature [11-14, 17, 20, 21], Models and measurements indicate that the effective thermal conductivity of particles loaded in a packed bed is generally limited to values below 5 W/m K, even with significant increases in the particle thermal conductivity (Fig. 4.4(b)). More clever methods must be employed to enhance thermal conductivity to levels above 5 W/m K. Additionally, the models discussed above have been developed for distinct particles typical of classic/interstitial hydride materials. These classic/interstitial beds are generally characterized as unsintered powders while complex hydrides, such as sodium alanates, can become porous sintered solids as seen in Fig. 4.5. Application of packed particle models have not been directly applied to sintered solid materials. 

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