Viscosity liquids/gases

The physical properties of spray-dried materials are subject to considerable variation, depending on the direction of flow of the inlet gas and its temperature, the degree and uniformity of atomization, the solids content of the feed, the temperature of the feed, and the degree of aeration of the feed. The properties of the product usually of greatest interest are (1) particle size, (2) bulk density, and (3) dustiness. The particle size is a function of atomizer-operating conditions and also of the solids content, liquid viscosity, liquid density, and feed rate. In general, particle size increases with solids content, viscosity, density, and feed rate. 

These mixers are specified when one liquid must be dissolved in another, a solid and a liquid must be mixed, a high viscosity liquid must be reacted, a light liquid must be extracted from a mixture of heavy and light liquids, or when gas must be absorbed in a liquid. To select the proper mixer, certain fluid properties must be know n ... 

The collection efficiency of wet scrubbers is dependent on parameters such as the size and quantity of liquid droplets, the liquid/gas ratio, high wa-ter-to-particle relative velocity, wettability of dust, particle density, gas viscosity, etc. For any specific application, the design procedure is to review operating data available from the technical literature or from manufacturers for similar applications. If data are not available, it may be necessary to per form pilot scale tests, which can be used for scale-up purposes. 

The orifice plate meter factor should be adjusted for actual operating parameters. For liquid streams, the flow meters should be adjusted for °API gravity, temperature, and viscosity. For gas streams, the flow rate should be adjusted for the operating temperature, pressure, and molecular weight. 

Hughmark and Pressburg (H14) studied holdup and pressure drop for cocurrent gas-liquid flow, and correlated holdup with a function of gas and liquid flow rates, surface tension, densities of gas and liquid, viscosities of gas and liquid, and total mass velocity. 

Unfortunately, relatively little information has been made available for industrial gas-liquid contactors. Further data from industry could permit significant tests of the reliability of the present correlations and their applicability to scale-up. Steel and Maxon (SI 1) reported on the power requirements during novobiacin fermentation in 20- and 250-liter pilot-plant vessels and in 12,000- and 24,000-gal vessels. The comparative data are difficult to evaluate because of changes that occurred in viscosity and gas retention during the course of the fermentation. In addition, geometric similarity did not prevail... 

Because of various gather status, liquids are quite different in properties fi-om gases. For IS the following are important (1) In density, liquid is greater than gas by about 10, (2) In viscosity, liquid is greater than gas by about 10, and (3) Molecules of gas have relatively large if ee-path, while those in stationary liquid can only vibrate and/or rotate round their balanced positions with extremely small displacement. These affect strongly the performances of IS. 

Mass transfer (the C term), which involves collisions and interactions between molecules, applies differently to both packed and capillary columns. Packed columns are mostly filled with stationary phase so liquid phase diffusion dominates. The mass transfer is minimized by using a small mass of low-viscosity liquid phase. Capillary columns are mostly filled with mobile phase, so mass transfer is important in both the gas and liquid phases. A small mass of low-viscosity liquid phase combined with a low-molecular weight carrier gas will minimize this term. 

In gas atomization via film or sheet breakup (Table 4.16), the mean droplet size is proportional to liquid density, liquid viscosity, liquid velocity, and film or sheet thickness, and inversely proportional to gas density and gas velocity, with different proportional power indices denoting the significance of each factor. In recent experimental studies on liquid sheet and film atomization processes using a close-coupled atomizer, Hespel et al. 32X concluded that the... 

A special area of HP NMR in catalysis involves supercritical fluids, which have drawn substantial attention in both industrial applications and basic research [249, 254, 255]. Reactions in supercritical fluids involve only one phase, thereby circumventing the usual liquid/gas mixing problems that can occur in conventional solvents. Further advantages of these media concern their higher diffusivities and lower viscosities [219]. The most commonly used supercritical phase for metal-catalyzed processes is supercritical CO2 (SCCO2), due to its favorable properties [256-260], i. e., nontoxicity, availability, cost, environmental benefits, low critical temperature and moderate critical pressure, as well as facile separation of reactants, catalysts and products after the reaction. 

Apart from the critical impeller speed for solid suspension and efficient gas dispersion, flooding is also a very important phenomenon in three-phase systems. Flooding may take place at low impeller speed or high gassing rate. Under these conditions, the gas is dispersed just around the central shaft of the tank, whereas the solids are settled at the bottom. Flooding characteristics are not affected by particles. Furthermore, high-viscosity liquids are able to handle more gas before flooding than low-viscosity liquids. 

In brief, increasing the gas-and liquid velocities or mass fluxes, the liquid viscosity, or gas density, or reducing the particle diameters, increases the pressure drop. 

In brief, the total external liquid hold-up is an increasing function of liquid velocity, viscosity and particle diameter. It is a decreasing function of the superficial velocity of the gas, and of the liquid surface tension. Liquid hold-up reduces as the gas density increases, except for very low gas velocities, where it is insensitive to gas density. Non-coalescing liquids exhibit much smaller hold-ups than coalescing liquids. Gas viscosity appears to have a marginal effect on the liquid hold-up. 

Next, procedures for estimating values of the coefficient of isothermal compressibility and oil viscosity are discussed. The chapter ends with methods of estimating hydrocarbon liquid-gas interfacial tension. 

When a pure gas such as HCl is absorbed by low viscosity liquid such as water, simple spray systems can also be highly effective. See Example 24. 

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