Settling rate acceleration

Laboratory Exercise Acceleration of Settling Rates by Coagulants... 

A considerable reduction of the time necessary for one analysis is obtained, however, if the analysis is performed in a centrifugal field. Due to the fact that the settling rate in a centrifugal field is increased over the stationary gravity settling rate by the ratio of centrifugal acceleration, a, to the gravity acceleration, g ... 

One realizes under laminar flow conditions, the acceleration distance, z, is directly proportional to the stationary settling rate, Wg, or the stop distance, sq. All other variables are constant for a given layout. It has been assumed in this system that the particles enter the flow of velocity, Va, with the constant initial velocity, Vpo. Fig.3 shows the relative velocity increase, Ac, with respect to the acceleration di-... 

One realizes from Fig. 3 that small particles attain, for example, 99% of the gas velocity after a very short distance. A 0.5 jxm particle, for example, needs approximately 0.8 mm, a 1 pm particle 4 mm to attain this relative velocity increase. The situation improves with coarser particles. The particle sizes, given in Fig. 3, are equivalent settling rate diameters. They have been calculated from the stationary settling rate, which controls the particle acceleration, for the sake of better demonstration. This system can be used for the measurement of settling rate distributions, if at a certain distance the increase of the particle velocity is measured for each individual particle. This has been used in an accelerated gas flow, as shown in 4.3. 

The basic equation may be derived as follows If one accelerates a certain mass flow rate, mg, of particles of a certain settling rate, Wg j, in a tube of constant cross section. A, a momentum balance yields the additional pressure drop, Apj i, at the distance, Tij, from the entry point of the particles ... 

The Measurement of Settling Rate Distributions in an Accelerated Flow... 

The capacity of any specific tank configuration, in terms of metric ton equivalents, is deterrnined by one of three parameters. (/) The solubiHty of waste salts. Precipitates can settle and cause thermal hot spots, which in turn can result in accelerated corrosion rates. Thus it is important to maintain the... 

Flocculation is accelerated and higher overflow rates are achieved by external or internal recirculation of settled soflds into the feed which leads to the collection of fine particles by interception. Addition of conditioned fine sand to the feed induces separation by differential sedimentation, and sometimes increases overflow rates to 6—8 m/h. 

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