Centrifugation density

Elevated peripheral eosinophil counts in asthmatics have correlated with decreases in specific airway conductance, forced expiratory volume (FEVi), maximum mid-expiratory flow rate (Horn et al., 1975), bronchial hyperreactivity (BHR) to histamine (H Taylor and Luksza, 1987) and clinical severity scores (Aas Bousquet et al., 1990). When circulating eosinophils were isolated fi om asymptomatic asthmatics, a large proportion of cells (35%) was recovered with centrifugal density less than 1.082 gml compared to normal subjects (10% Frick et al., 1989). Alteration of centrifugal density of eosinophils is one of the phenotypic responses to cellular activation (Hansel et al., 1990 Fukuda and Makino, 1992). Not only is the number of cells increased in asthma, circulating eosinophils may be activated intravascularly as well. 

When a fuel requires centrifuging, density is a critical property and as the density of the fuel approaches the density of water (API gravity = 10°C) the efficiency of centrifuging decreases (ASTM D-2069). When separation of water from the fuel is not required, density is not a significant measure of fuel quality but it may give useful information when used in conjunction with other tests. 

In an extract oil refining process, oil and aqueous phases are to be separated in a centrifuge. Densities of oil and aqueous phases are, respectively, 919.5 kg/m and 980.3 kg/m. Overflow radius for light liquid is 10.16 mm. Outlet for the heavier liquid is 10.414 mm. Find interface location. 

The density of heavy fuels is greater than 0.920 kg/1 at 15°C. The marine diesel consumers focus close attention on the fuel density because of having to centrifuge water out of the fuel. Beyond 0.991 kg/1, the density difference between the two phases —aqueous and hydrocarbon— becomes too small for correct operation of conventional centrifuges technical improvements are possible but costly. In extreme cases of fuels being too heavy, it is possible to rely on water-fuel emulsions, which can have some advantages of better atomization in the injection nozzle and a reduction of pollutant emissions such as smoke and nitrogen oxides. 

The general analysis, while not difficult, is complicated however, the limiting case of the very elongated, essentially cylindrical drop is not hard to treat. Consider a section of the elongated cylinder of volume V (Fig. II-18h). The centrifugal force on a volume element is u rAp, where w is the speed of revolution and Ap the difference in density. The potential energy at distance r from the axis of revolution is then w r Apfl, and the total potential energy for the... 

Illustration showing separation by equilibrium-density-gradient centrifugation. The homogeneous mixture in (a) separates into three bands (b) after applying centrifugal force. 

Sodium carbonate monohydrate crystals from the crystallizers are concentrated in hydroclones and dewatered on centrifuges to between 2 and 6% free moisture. This centrifuge cake is sent to dryers where the product is calcined 150°C to anhydrous soda ash, screened, and readied for shipment. Soda ash from this process typically has a bulk density between 0.99—1.04 g/mL with an average particle size of about 250 p.m. 

The pressure-volume curve of a proposed centrifugal fan has a different shape. This fan curve must be drawn for the anticipated fan inlet density expected at its location in the system. The point of intersection of these two curves locates the flow rate and pressure rise at which the fan and system operate. This intersection represents a desirable operating combination for fan and system. The system curve intersects the fan curve in the middle of its maximum efficiency range and also at a point where the fan pressure produced varies smoothly but distinctly in a constant trend with flow rate which is desirable for flow control. 

Fig. 1. Distribution of component cells by density in a centrifuged sample of human blood.

Density is a particularly important characteristic of alloys used in rotating machinery, because centrifugal stresses increase with density. Densities of the various metals in Table 1 range from 6.1 to 19.3 g/cm. Those of iron, nickel, and cobalt-base superaHoys fall in the range 7-8.5 g/cm. Those alloys which contain the heavier elements, ie, molybdenum, tantalum, or tungsten, have correspondingly high densities. 

In dye-binding tests, milk is mixed with excess acidic dye solution where the protein binds the dye in a constant ratio and forms a precipitate. After the dye—protein interaction takes place, the mixture is centrifuged and the optical density of the supernatant is determined. Utilization of the dye is thus measured and from it the protein content determined. Several methods for appHcation of dye-binding techniques to milk are given (24,25). 

Gravity, or centrifugation rarely provide enough hydrostatic pressure to force Hquid into nonwetting pores. If the Hquid wets the soHd the clump density increases as gas is displaced from the interior. It is best if submersion does not occur until the Hquid has completely displaced gas from the pores (Fig. 2). For wetting Hquids and pores with average diameter, D-pQ- y and tortuosity,the length, to which Hquid is pulled into a bed of powder by... 

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