SEDIMENTATION STUDIES APPARATUS

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Description

Settling or sedimentation is the separation of solid particlesfrom fluids under the gravitational force. When a solidparticle moves in a fluid. Then a number of forces are actingon it:1. The gravitational force, acting downward.2. The buoyant force, acting upward.3. The drag force, acting upward.When a particle fall in a fluid under constant force, e.g. forceof gravity, then particle accelerates for some time, but whenthe accelerating force equals the retarding force (Buoyantforce and Drag force) then the resultant force acting on theparticle will be zero, and particle quickly reaches velocity,which is the maximum attainable under the circumstancesand which is called the terminal velocity. When slurry isprepared in a container and then allowed to remainundisturbed for some time, four settling zones will appear asbelow:A Supernatant Layer C Transition Zone B Slurry Zone D Concentration Sludge Zone.With the passage of time, the height of the different zoneswill vary and ultimately zone A of clear liquid and zone D ofthe sludge will be left. When all the solid particles settle inzone D, then this is critical stage and after this no settlingtakes place. With further passage of time, the height of thezone D will decrease due to the compression of the sludgeon account of its own weight. Settling can be free settling orhindered settling. But most of the slurries settle underhindered conditions. Free settling is that in which the motionof one particle is unaffected by the motion of the otherparticle while in case of hindered settling many particles arepresent so there is mutual interference in the motion of theparticles and the velocity of motion or rate of settling isreduced.The present set-up with 5 Nos. of Borosilicate Glass Graduated Cylinders is designed to study the zone settlingdepending upon the concentration and characteristics of theparticles. These cylinders can be easily removed for cleaning.Rate of change in height of the various liquids/solidsinterfaces with respect to time can be measured with thehelp of stop watch.