Design aspects and performance of a settling tube system

Design aspects and performance of a settling tube system

Slot, R.E.
Geldof, H.J.

Civil Engineering and Geosciences

Hydraulic Engineering

1979-01-01

The DUST (Delft University Settling Tube) is a settling tube system intended to analyse particle size (settling velocity) of sand ranging from 0.06 mm to 2 mm, with the sample mass varying from 0.5 g to 20 g. The main parts of the system are (see fig. 1): a. the sample introduction device (venetian blind with rotating lamellae) b. the settling tube c. the measuring device (underwater balance with feedback) All particles of a sample are released by the sample introduction device at the same time, after which they pass the settling tube. Finally they come at the balance, which measures more or less instantaneously the weight of the particles, thus yielding a cumulative settling velocity distribution. Dimensions and characteristics of the instrument and the measurement procedures have to be chosen such that the final error in the distribution function attains a minimum. Several of the relevant aspects are treated in the next sections. CONCLUSIONS a. Using an underwater balance with feedback, it is possible to measure the settling velocity distribution of (sand) particles ranging from 0.1 to 2 mm with an accuracy (systematic part of the error) better than 7%, in which 5% is due to the settling phenomenon itself (concentration effects). The precision (random part of the error) is better than 2%, including the error of sample splitting. The accuracy of the (relative) weight-measurement is better than 0.1% with a precision better than 0.5%. b. The impact of the particles can'be interpreted as a contribution to the delay time of the weighing system. As the impact partly compensates the delay time of the weighing system, the demands upon the delay time can be weakened. Given the possible velocity range, there is an optimum value of the delay time, for which the error will be smaller than 0.25 gy^2/L. c. Further research has to be done on the dependence of the settling phenomenon on the average particle diameter, the scatter in particle diameter, the diameter of the settling tube and the temperature of the sedimentation fluid.

settling tube
settling
settling velocity
design aspects
performance
DUST
characteristics

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TU Delft, Department of Hydraulic Engineering

Report no. 6-79

Institutional Repository

report

(c) 1979 TU Delft, Department of Hydraulic Engineering