Sedimentation tube

Gravitational settlement is allowed to proceed for 4 to 10 minutes, according to the particle-size range of the sample. The sedimentation tube is then centrifuged to reduce the time required for the smaller particles to reach the bottom. By measuring the volume of particles accumulated as a function of time, the equivalent spherical size distribution of the sample may be computed from formulae based upon Stokes law. In addition to the specially designed sedi-... 

Another sedimentation method used is the so-called MSA-analyzer. If the value of "g" in 5.10.8. is increased (such as the use of a centrifuge) one can analyze the very smaU particles in any given distribution in a short time. The problem of course lies in accurate determination of the weight accumulated at a given time under a specific centripetal force. This problem has been neatly solved by careful design of the sedimentation tube, as shown in the following diagram ... 

The batch thickener usually consists of a cylindrical tank with a slightly conical bottom. After sedimentation has proceeded for an adequate time, the thickened liquor is withdrawn from the bottom and the clear liquid is taken off through an adjustable offtake pipe from the upper part of the tank. The conditions prevailing in the batch thickener are similar to those in the ordinary laboratory sedimentation tube, and during the initial stages there will generally be a zone in which the concentration of the suspension is the same as that in the feed. 

Solubiliiy in Nitric Acid. Add an 80 g sample with stirring to 100 g of 97.5 to 99-0% nitric acid in a 200 ml beaker. After allowing the soln to cool, transfer a 100 ml portion to a 100 ml Goetz (or equal) oil sedimentation tube and centrifuge at 1800 rpm for 20 mins, using an 8-in centrifuge head. 

On the other hand many methods have been devised for measuring pressure changes with time at a given point in the sedimentation tube. These methods are based on the so-called Wiegner (1918) sedimentation tube. This tube consists of a cylinder with relatively large diameter. At a point -distant from the top is attached a smaller tube provided with a stopcock. This tube is bent upward parallel to the sedimentation tube. The smaller tube is filled with sedimentation fluid, free of particles, to the level of the suspension itself in the sedimentation tube. When the stopcock is opened the liquid in the smaller tube rises as sedimentation progresses, the liquid in the smaller tube decreases. 

Figure 16. Good-hue and Smith Sedimentation Tube for Particle - size Determination.

In use the light beam and photoelectric cell may be moved up or down along the axis of the sedimentation tube. Thus, the time required to obtain a sedimentation curve of the suspension may be shortened considerably. By adjustment of the lamp and photoelectric cell to any level it is not necessary to wait for small particles to settle to a given level. If a level has been chosen to which particles less than d units in size have settled at a given time, then... 

To sample the settling flux directly, free-floating multiple-sample programmable sediment traps (Pro-Trap) were deployed at all three fjords for about 16 h at each time (trap depth 60 m). The Pro-Trap system consists of four polyvinyl chloride (PVC) sediment tubes, each of 0.018 square meter exposed area (cylinder height of 80 cm, trap aspect ratio A 4 5.3), mounted on a stain-less-steel frame. Depth and angle sensors allowed defining the position of the traps in the water... 

One sediment tube, devoted to the determination of 234Th, took a single sample for the entire duration of each deployment. On recovery of the... 

Koglin [56] continued Johne s work with an emphasis on wall effects and attributed the difference between the two earlier investigations to these effects. Since Boardman visually determined the settling time between two marker lines on the sedimentation tube, he selected particles in the center of the tube, whereas Johne s method was non-selective. 

The analyzer described by Simons and Williams [65] consisted of an array of eight pairs of capacitance electrodes mounted vertically down the side of a sedimentation tube of length 26 cm and diameter 2.5 cm. The electrodes were embedded in acrylic and flush mounted to the inside wall of the tube. 

Dielectric Sedimentation Method. The measurement relies upon the sensing of changes in the dielectric constant of medium between a pair of capacitance sensing plates placed around the sedimentation tube. 

The oil tank is usually constructed of stainless steel and may have a rectangular shape or a V-shaped bottom. The V-shaped bottom facilitates settling and removal of sediment. Tubes or electrical elements may be placed in the tank, if an internal heating system is used. The thermal insulation of the tank is a very important feature since it improves fryer efficiency and lessens the risk of burns to those making casual contact. Some metals are strong catalysts of oil oxidation. Their eatalytic activity varies following the order copper > copper alloys > iron > zinc > stainless steel > magnesium. Copper and copper alloys are detrimental for oil deterioration therefore, all metal surfaces that come in contact with the oil should not contain any of these metals. 

Ultrasonic velocity and absorption at various heights in the cream or sedimentation tubes. 

Figure 4.8. Appearance of the Werner sedimentation tube along with data comparing the performance of the Werner tube to the Phototrack equipment.

The first line start sedimentation procedure based on centrifugal sedimentation was described by Marshall [46], who was aware of the problems involved in floating a layer of suspension onto a column of clear fluid because of reported difficulties with the Werner sedimentation tube discussed in the previous section. He attempted to achieve a stable suspension system by using a suspension of lower density than the liquid column through which the fineparticles were to be sedimented. He used a sucrose solution for the column fluid and a water-based suspension of fineparticles. This strategy as discussed earlier only eliminates gross inversion of the layer of suspension. 

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