Effect of Operating Conditions

A unique feature of the dense-phase fluidized bed is the existence of a maximum convective heat transfer coefficient /zmax when the radiative heat transfer is negligible. This feature is distinct for fluidized beds with small particles. For beds with coarse particles, the heat transfer coefficient is relatively insensitive to the gas flow rate once the maximum value is reached. 

For a given system, hmm varies mainly with particle and gas properties. For coarse particle fluidization at U Umf, the heat transfer is dominated by gas convection. Thus, /tmax can be evaluated from Eq. (12.50). On the other hand, hmax in a fine particle bed can be reasonably evaluated from the equations for hpc. In general, hmM is a complicated function 

12 / Heat and Mass Transfer Phenomena in Fluidization Systems 

At high temperatures, the decreased gas density can decrease the gas convective component /tgc. On the other hand, the increased gas conductivity at high temperature can increase /tgc, Ke, and hpc- For a bed with small particles, the latter is dominant. Thus, a net increase in hc with increasing temperature can be observed before radiation becomes significant. For Group D particles, hc decreases with increasing temperature [Knowlton, 1992]. The effects of temperature and pressure on hpc, /igc, and Amax are illustrated by Fig. 12.13. 

For radiative heat transfer, some differences between a fluidized bed and a fixed bed exist [Kovenskii, 1980]. When a bed starts to fluidize from the fixed state, the radiative heat transfer rapidly increases by 10-20 percent it remains constant as the gas velocity increases further in the bubbling bed. 

Moisture content of the plant material, microwave power, and extraction time affect not only the extraction yield of the essential oil but also its composition. Sample moisture content during microwave treatment is critical, because water is an 

The efficiency of SEME extraction, in terms of yield and composition of the essential oil, can usually be increased by increasing all three of these factors. 

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Fig. 6. Flux versus concentration, illustrating the effect of operating conditions on K and deviations from equation 6.

Mathews and Rawlings (1998) successfully applied model-based control using solids hold-up and liquid density measurements to control the filtrability of a photochemical product. Togkalidou etal. (2001) report results of a factorial design approach to investigate relative effects of operating conditions on the filtration resistance of slurry produced in a semi-continuous batch crystallizer using various empirical chemometric methods. This method is proposed as an alternative approach to the development of first principle mathematical models of crystallization for application to non-ideal crystals shapes such as needles found in many pharmaceutical crystals. 

One of the common problems associated with underwater pelletizers is the tendency of the die holes to freeze off. This results in nonuniform polymer melt flow, increased pressure drop, and irregular extrudate shape. A detailed engineering analysis of pelletizers is performed which accounts for the complex interaction between the fluid mechanics and heat transfer processes in a single die hole. The pelletizer model is solved numerically to obtain velocity, temperature, and pressure profiles. Effect of operating conditions, and polymer rheology on die performance is evaluated and discussed. 

Topal, U. et al.. Extraction of lycopene from tomato skin with supercritical carbon dioxide effect of operating conditions and solubility analysis, J. Agric. Food Chem., 54, 5604, 2006. 

Morf LS, Brunner PH, Spaun S (2000) Effect of operating conditions and input variations on the partitioning of metals in a MSWI. Waste Manag Res 18(1) 4—15... 

In order to allow the estimation of the kinetic parameters involved in the development of a detailed FT kinetic model, the effects of operating conditions on both... 

Effect of Operating Conditions. Yield data, summarized in Figures 1 and 2, point to acetic acid homologation activity being sensitive to at least four operating variables, viz. ruthenium and methyl iodide concentrations, syngas composition and operating pressure. 

Moreover, the effect of operating conditions (applied current, electrolyte concentration, air flow rate and pH) on the amount of electrogenerated H202 was investigated [94] ... 

The aim of this work is to study the incorporation of cadmium and phosphate in the three calcium sulfate modifications. The uptake of other metal ions in AH will also be described. Kinetic effects of operating conditions such as the residence time, sulfuric acid and phosphate concentration upon the phosphate and cadmium uptake has been investigated. In addition the influence of a growth retarding impurity, AIF3, on the cadmium and phosphate uptake will be given. 

Effects of Operating Conditions on Transfer of Gradient Methods.148... 

M. Grotti, C. Lagomarsino and J. M. Mermet, Effect of operating conditions on excitation temperature and electron number density in axially-viewed ICP-OES with introduction of vapors or aerosols, J. Anal. At. Spectrom., 21(9), 2006, 963-969. 

Wetzel (75) atomized both molten wax and a molten alloy in a Venturi nozzle and established empirical equations for expressing the magnitudes of the effects of operating conditions on the particle-size distribution of the spray. An advantage of molten alloy is that a permanent record of the spray is obtained and large numbers of particles may be sized by physical methods. 

A detailed examination of the effects of operation conditions on boria on alumina catalyst performance and lifetime is reported in this paper, in an attempt to further elucidate the important parameters controlling optimisation and maintenance of caprolactam yield. 

Saitua, H., Campderro s, M., Cerutti, S. and Padilla, A.P. (2005) Effect of operating conditions in removal of arsenic from water by nanofiltration membrane. Desalination, 172(2), 173-80. 

Effect of Operating Conditions on Grafting Efficiency and Conversion. ... 

The total acidity deterioration and the acidity strength distribution of a catalyst prepared from a H-ZSM-5 zeolite has been studied in the MTG process carried out in catalytic chamber and in an isothermal fixed bed integral reactor. The acidity deterioration has been related to coke deposition. The evolution of the acidic structure and of coke deposition has been analysed in situ, by diffuse reflectance FTIR in a catalytic chamber. The effect of operating conditions (time on stream and temperature) on acidity deterioration, coke deposition and coke nature has been studied from experiments in a fixed integral reactor. The technique for studying acidity yields a reproducible measurement of total acidity and acidity strength distribution of the catalyst deactivated by coke. The NH3 adsorption-desorption is measured by combination of scanning differential calorimetry and the FTIR analysis of the products desorbed. 

Chemical vapor deposition is a key process for thin film formation in the development and manufacture of microelectronic devices. It shares many kinetic and transport phenomena with heterogeneous catalysis, but CVD reactor design has not yet reached the level of sophistication used in analyzing heterogeneous catalytic reactors. With the exception of the tubular LPCVD reactor, conventional CVD reactors may be viewed as variations on the original horizontal reactor. These reactors have complex flow fields and it is consequently difficult to control and predict the effect of operating conditions on the film thickness and composition. 

The effect of operating conditions in the formation of these in situ films is likely to be complex. In 1972 Forbes showed that even under fairly mild conditions with an anti-wear additive such as tricresyl phosphate surface films are formed which contain both phosphorus and organic fragments. Similarly Cann showed that a cross-linked thick surface film is formed from zinc dialkyidithiophosphate under mild rubbing conditions. It seems probable that at least some of the soluble molybdenum compounds would also experience partial breakdown under mild rubbing conditions, and that these would encourage the formation of protective surface films. 

Chrastil s equation was adopted in the systematic study of binary solubility behavior because it is easy to use and it does not require information on the properties of lipid components. Its parameters can then be used to interpret the effect of operating conditions on solubility. Its value, however, is limited for predictive modeling of solubility data, which should involve in-depth thermodynamic models (e.g., using an Equation of State (EOS) approach), describing all the phases present at equilibrium. 

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