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HM 142


Technical Description

In sedimentation tanks, solids are separated out of suspensions under the influence of gravity. For this, the density of the solid particles must be greater than that of the liquid.

With HM 142, the factors influencing the separation process in sedimentation tanks can be investigated. First a suspension of water and precipitated calcium carbonate is prepared in a tank. A pump delivers the suspension to the sedimentation tank. In the inlet area of the sedimentation tank the suspension intermingles with fresh water. The mixture flows over an inlet weir. On their way through the sedimentation tank the solids sink to the bottom. The treated water flows out by way of the weir at the sedimentation tank outlet.

The solid concentrations at the sedimentation tank inlet and outlet are determined by means of two Imhoff cones. The mass separated in the sedimentation tank can be determined from the difference between them. The flow rates of the suspension and the fresh water are adjusted by valves and indicated by flow meters. This enables the mixing ratio - and thus the solid concentration of the mixture - to be adjusted. In order to ensure a uniform mix of the suspension and prevent premature sedimentation, a portion of the suspension is fed back into the suspension tank by way of a bypass. To investigate the flow conditions, ink can be added with a piston burette to the fresh water stream as a tracer substance. The mixed-in volume of ink is entered using keys and indicated on a display. To provide enhanced observation of the flow conditions and settling processes, the sedimentation tank is made of transparent material.

A baffle plate can be positioned in the sedimentation tank to impede the flow. Its horizontal and vertical positioning in the sedimentation tank is adjustable. This enables the flow conditions and the efficiency of the separation process to be influenced.

The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.

Learning Objectives / Experiments

- learning the fundamental principle of separation of solids from suspensions in a sedimentation tank
- efficiency of the separation process dependent on
  * solid concentration of suspension 
  * flow rate
  * position of baffle plate
- investigation of flow conditions dependent on
  * flow rate
  * position of baffle plate


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