Settling velocity measurement

Performed time-dependent calculaions at low Reynolds numbers reported the existence of regions of high deformation near stagnation points, especially downstream from it Perturbation analysis and obtained an approximate stream function Orientation and settling velocity measurements... 

Measurement of single particle settling velocity in a turbulent field is not easy. However, it is known to be a function of free settling velocity which for spherical particles can be estimated from the following ... 

Quite often the settling velocity is modified by the presence of a large number of particles. This hindered settling velocity is a function of soHds concentration and should be measured experimentally or estimated from Hterature correlations (1). 

Fig. 8. Sedimentation equipment performance where the particles have a A5 value of 1.0 g/cm and a viscosity, p., value of 1 mPa-s(=cP). The value of is twice the settling velocity at G = 1, and Q = overflow discharge rate in measurements given.

For solid-liquid systems, settling velocities of the 10, 50. and 90 percent by w eight fractions of particle size distribution must be available from calculations or measurements. 

Parameter P is equal to the ratio of the liquid volume entrained and the sum of the volumes of this liquid and particles. Values of P are determined experimentally from measured settling velocities. In general, the smaller the effective particle size, the more liquid is entrained by the same mass of solids phase. For example, particles of carborundum with d = 12.2 //.m have P = 0.268 d = 9.6 ftm, p — 0.288 and d = 4.6 fim, p = 0.35. 

With particles, the contaminant concentration in the duct is determined by isokinetic sampling with subsequent laboratory analysis use of a calibrated direct reading instrument. If the concentration distribution in the duct is uneven, a complete survey of the concentration distribution with the corresponding duct velocities and cross-sectional area is required. National and ISO standards provide information on isokinetic sampling and velocity measurements. In the case of particles, the airborne emission differs from the total emission, for example in the case of granular particulate. The contaminant settling on surfaces depends on particle distribution, airflow rates, direction in the space, electrical properties of the surfaces and the material, and the amount of moisture or grease in the environment. 

V = Settling velocity for hindered uniform spherical particle, ft/s or m/s Wi= Width of rectangular cone inlet duct, ft Z], = Heavy phase outlet dimensions of decanter measured from horizontal bottom, shotvn on Figure 4-12... 

Azetsu-Scott K, Johnson BD (1992) Measuring physical charcteristics of particles a new method of simultaneous measurements for size, settling velocity and density of constituent matter. Deep-Sea Research 39 1057-1066... 

Although the sedimentation velocity of particles tends to decrease steadily as the concentration of the suspension is increased, it has been shown by Kaye and Boardman11 that particles in very dilute suspensions may settle at velocities up to 1.5 times the normal terminal falling velocities, due to the formation of clusters of particles which settle in well-defined streams. This effect is important when particle size is determined by a method involving the measurement of the settling velocity of particles in dilute concentration, though is not significant with concentrated suspensions. 

Settling velocities of such particles have been measured by Pettyjohn and Christiansen (P6) and Chowdhury and Fritz (Cl). Correlation of both sets of data with the results of Heiss and Coull for cubes gives ... 

Instruments are commercially available that automatically carry out the analysis presented above. Although much of the tedium of the experiment is thereby relieved, automation does not alter the basic assumptions and/or approximations of the method. In one commercial instrument, a collimated beam of light or low-energy x-rays scans the settling compartment, measuring the absorbance of the suspended particles at various depths. Because the detector does not have to wait for settling particles to arrive at a fixed position, this method is more rapid than direct observation of sedimentation. A built-in computer converts the absorbance at a particular distance below the top of the sample to concentration after some time has elapsed from the start of settling. The distance-time combination is reduced to a velocity,... 

Solids suspension involves producing the required distribution of solids in the tank and is essentially a physical phenomenon. The criterion is normally a physical description of the degree of uniformity required in the suspension. A key variable for solids suspension is the settling velocity of the solids. This is usually measured by timing the fall velocity of individual solid particles in a defined depth of... 

Sternberg, R.W., Berhane, I., and Ogston, A.S. (1999) Measurement of size and settling velocity of suspended aggregates on the northern California continental shelf. Mar. Geol. 154, 43-53. 

A 200-p.m-diameter raindrop falls freely in the atmosphere. Determine its terminal settling velocity. Compare this to the measured value given in Table 5.3. 

Cunningham correction factor for, 63 settling velocity of, 81-82 Simple coagulation theory, 308 Simple diffusion, 131-143 Single-particle scattering measurements, 297-299... 

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