Uniformity coefficient

A Gaussian distribution of particle size is the result of copolymer manufactured by suspension polymerization. A jetting process produces beads with more uniform particle size. The uniformity coefficient is a numerical method of indicating closeness of all beads to the same size. 

The flotation unit maximum loading is 2.1 L/s/m2 (3.1 gal/min/ft2). The maximum filtration rate is 1.7 L/s/m2 (2.5 gal/min/ft2). Each filter compartment is backwashed at or more than 10.2 L/s/m2 (15 gal/min/ft2) during the backwash operation. The single-medium backwash filter consists of 28 mm (11 in.) high-grade silica sand. The effective size and uniformity coefficient for the sand are 0.35 mm and 1.55, respectively. 

Plot of a sieve analysis of a sample of run-of-bank sand is shown in Figure 7.9 by the segmented line labeled stock sand. This sample may or may not meet the required effective size and uniformity coefficient specifications. In order to transform this sand into a usable sand, it must be given some treattnent. The figure shows the cumulative percentages (represented by the normal probability scale on the ordinate) as a function of the increasing size of the sand (represented by the size of separation on the abscissa). 

Example 7.1 If the effective size and uniformity coefficient of a proposed hlter is to be 5(10 ) cm and 1.5, respectively, perform a sieve analysis to transform the run-of-bank sand of Figure 7.9 into a usable sand. 

Uniformity coefficient—The ratio of the size of the sieve opening that passes the 60% finer of the medium sample (Pgo) to the size of the sieve opening that passes the 10% finer of the medium sample. 

A consultant decided to reconunend using an effective size of 0.55 mm and a uniformity coefficient of 1.65 for a proposed filter bed. Perform a sieve analysis to transform a run-of-bank sand you provide into a usable sand. 

Fig. I a, b. Plots for the determination of uniformity coefficients (reliability function) of phenolic foam samples during tensile tests (a) normal (Gaussian) distribution (b) Weibull s distribution )...

The last factor is either the cohesion or the coef-Acient of uniformity. Cohesion is used with powders (very fine particles) or with materials on which an effective cohesion force can be measured. The uniformity coefficient is used with granular and powdered granular materials on which an effective surface cohesion cannot be measured. 

The uniformity coefficient is arrived at by dividing the width of the sieve opening that passes 10% of the sample. It is determined from a screen analysis of the material. The more uniform a mass of particles is in both size and shape, the more flowable it is likely to be. 

The value of C varies with the uniformity coefficient Cu = D6o/Diq, as shown in Table 2.5. 

Figure 4.1 Empirical relationships among grain size, uniformity coefficient, and permeability.

Another, this time indirect, method of assessing flowability was proposed by Carr36. This was based on measuring four properties of the powder (angles of repose and spatula, compressibility and uniformity coefficient, all as defined by Carr36) and, by awarding points (out of 25) for each, the sum total was then a measure of flowability and called Carr s Index . A commercial piece of equipment is available (Hosokawa Powder Characteristics Tester) for measuring the properties necessary for Carr s Index. 

In Chapter 6 we have learned that heat transfer coefficient varies with the distance from the entrance of a pipe. However, so far in this chapter we have assumed a uniform coefficient throughout the exchanger. This assumption coupled with mean fluid properties usually gives satisfactory answers. Yet in situations involving chain polymers... 

For formation solids characterization, a uniformity coefficient, C, given by the following expression, can be used (68) ... 

C uniformity coefficient used to characterize formation particle... 

Randomness of the residuals (Straume Johnson, 1992 Comish-Bowden, 1995). If the observed rates tmly have uniform coefficient of variation, the difference should tend to increase in absolute magnitude as the calculated rate increases. On the other hand, if the observed rates really have constant standard deviations, the simple differences should be scattered in a parallel band about zero, as in Fig. 6. 

Soil name Mean diameter (mm) Uniformity coefficient... 

The uniformity of the soil material, desirable in most cases, is quantified by reference to the uniformity coefficient and the coefficient of curvature. The uniformity coefficient (Cu) and the coefficient of curvature (Cq) are determined by the following equations ... 

Figure 7.13 shows PSDs for several salts typical of the various classes. Curve 1 is a Canadian potash. Curve 2 is an Italian vacuum salt. Curves 3 and 4 are two samples of the same Bahamian solar salt from two different final suppliers. Curve 5 is a typical dissolver-grade rock salt. All distributions depart from true lognormal by the presence of too much fine material. As shown by the uniformity coefficients, the solar salts have the widest PSDs and the vacuum salt the narrowest. Figure 7.14 shows the variation in PSD caused by screening. All three curves are for rock salt from Weeks Island (United States). These are well-screened fractions whose distributions are closer to lognormal. The uniformity coefficients are about 1.5. 

The resin in its sodium form has a bead specific gravity greater than 1.1 but a bulk density of only about 0.75. The effective size of a bead is about 0.5 mm, and the PSD is fairly narrow (uniformity coefficient < 1.7). Like most ion-exchange resins, it has a great capacity for holding water ( 60-65%). 

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